Power Plant Operation 3b4t3p

IG/05 (Restricted Circulation Only)

POWER PLANT OPERATION

Power Management Institute NOIDA

CONTENTS

S.No.

Description

Page Nos.

1.

Boiler Auxiliaries (210 MW)

1

2.

Boiler

9

3.

Turbine Auxiliaries

46

4.

Turbine

57

5.

Generator Auxiliaries (210 MW)

91

6.

Generator

97

7.

General Operating Instructions

119

8.

500 MW Operations

136

9.

10.

General Guidelines for Unit Load Chang es and Hot Restart 500 MW Turbine Operation (KWU)

147

157

1

MILLING SYSTEM

1.1

Most efficient way of utilising coal for steam generation is to burn it in pulverised form. The coal is pulverised to a fineness such that 70-80% es through a 200 Mesh sieve. Normally low speed ball mills or medium speed vertical spindle mills are employed in power station for this purpose. The factors that affect the operation of the mill (whereby reducing the output) are as follows:

1.1.1

Grindability of coal: If harder coal is fed to the mill (i.e. coal having lower hardgrove index) then mill output gets reduced and vice versa.

1.1.2

Moisture content of coal: More the moisture content in coal, due to limitation in drying capacity lesser will be the mill output & vice versa.

1.1.3

Fineness of output: If output desired is of more fineness then there is corresponding capacity reduction of mill.

1.1.4

Size of coal input: If the raw coal size fed to the mill is of larger size then mill output will reduce.

1. 1.5

Mill wear: More wear and tear of grinding elements reduce the output from mill.

1.2

The trend normally, these days, is to use medium speed vertical spindle mills with pressurised system. The typical checks for starting a milling system are described below:

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2.

PRE START CHECKS (Typical: Raymond Bowl Mill)

2.1

Local: (to be made by local operator)

2.1.1

-

Ensure R.C. Bunker level satisfactory.

2.1.2

-

R.C. feeder and mill properly boxed up and no maintenance staff working.

2.1.3

-

Gear box oil level normal.

2.1.4

-

Lub. oil coolers charged.

2.1.5

-

Tramp iron gate open.

2.1.6

-

Cold air gate open. Hot air gate closed.

2.1.7

-

Mill outlet valve open

2.1.8

-

2.1.9

-

2.2

Take out emergency push button and give clearance to UCB for

Seal air valve open. Mill fire fighting system ready.

starting. 2.3

U.C.B.: (to be made by desk operator)

2.3.1

-

Ensure no PTW pending.

2.3.2

-

Ensure at least one P.A. fan and a seal air fan is in service. Check the header pressure for both primary and seal air is normal.

2.3.3

-

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Check that mill ignition energy is O.K.

2

2.3.4

-

Check that mill start permissives as per FSSS are satisfied (for the help of operator these permissives are written on FSSS and when the condition is satisfied it is indicated by a glowing bulb).

2.3.5

-

Ensure E.P. zones have been charged (for first mill) .

2.3.6

-

Ensure attemperation valves are ready for operation.

2.3.7

-

Inform turbine operator of mill start up.

2.3.8

-

Get the electrical supply for the mill.

2.3.9

-

Inform the local operator to be near mill for start up.

2.4

Start the mill

3.

POST START CHECKS

3.1

Local

3.1.1

-

Check no abnormal sound from mill.

3.1.2

-

Check return oil flow from upper bearing is satisfactory.

3.1.3

-

Check all the rollers are rotating and the rate of reject is normal (after the mill is loaded).

3.2

U.C.B.

3.2.1

-

Check mill starting time and current. Ensure that they are normal.

3.2.2

-

Open hot air gate.

3.2.3

-

Warm up the mill

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3.2.4

-

Start the RC feeder and load the mill gradually

3.2.5

-

Keep the air flow through mill - 54 T/hr.

3.2.6

-

Keep watch on mill differential to avoid mill choking.

3.2.7

-

Maintain mill outlet temperature between 75°C to 80°C.

3.3

-

As the pressure, temperature of main steam shoots up with coal firing proper check should be kept on these parameters. (Especially for first mill).

DRAFT SYSTEM 4.

FAN OPERATION

4.1

The Operation of fan depends on the type of fan to be started but there are several common prestart checks.

4.2

For large units, the fan start up is invariably sequence controlled, wh ich means that once the button is pressed, an automatic checking system ensures that all systems associated with the fan are in good working order. Nevertheless a considerable number of 'on line' interlocks must be satisfied before the main motor is energised. (Refer fig.1 for typical fan operation).

4.3

The common prestart checks which are essential are as follows:

5.

LOCAL CHECKS (to be made by local operator)

5.1

Generally inspect the fan. Ensure no maintenance staff working and all manholes etc. closed.

5.2

Check Discharge damper closed.

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5. 3

Check Regulating vanes minimum.

5.4

Ensure lub oil tank level is normal. Start lub oil pump. Check auto operation of standby pump. Check lub oil pressure, flow and temperature. Charge lub oil coolers.

5.5

Check control oil pressure, adjust if necessary. (for reaction fans).

5.6

Charge motor cooler from water side (if provided).

5.7

Check fan/fan motor bearing temperatures are normal.

5.8

Take out emergency push button and given clearance to UCB for starting the fan.

6.

CHECKS IN UCB : (By desk Operator)

6.1

Ensure no PTW pending.

6.2

Line up the flue gas path.

6.3

Ensure discharge damper closed, regulating vanes minimum, lub-oil pressure O.K. (UCB indications).

6.4

Ensure interlocked auxiliary is in service

6.5

Ensure fan/fan motor bearing temperatures are normal.

6.6

Ensure fan protections and interlocks have been checked and are O.K. (this is to be done if fan is being started after long shutdown).

6.7

Get the electrical supply from HT/LT operator.

6.8

Check R/TPR position is normal.

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FIG. 1

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6.9

Ask the local operator to be at site and inform him when the fan is to be actually started.

6.10

Start fan. Note down starting current and time.

6.11

Check that fan discharge damper opens on interlock after preset time delay. Check the operation of interconnecting dampers. (If dampers provided are manual then the discharge damper is to be opened and interconnecting dampers to be closed manually).

6.12

Check locally for bearing vibrations, abnormal sounds etc., they should be within normal limits.

6.13

The above checks can only be regarded as examples, as fan operation vary from station to station and the correct operating procedure as suggested by Manufacturer must be followed.

6.14

It is important to note that the fans take heavy starting current and long starting times. So always allow the fan amperage to fall to minimum value before starting the next fan. Starting fans in rapid succession can result in transformer overload.

7. 7.1

ELECTROSTATIC PRECIPITATORS The boiler pressure will be raised initially on oil burners, as P.F. mills can not be commissioned until the air heaters are fully in service and combustion air temperatures are adequate to ensure good combustion. Electrostatic precipitators are not normally taken into service (i.e. the zones are not changed) when firing on oil only (Oil vapour deposits are not conducive to good EP efficiencies) and, if possible, the EP should be byed whilst firing on oil only. This is done to prevent oil deposition on electrodes which can reduce E.P. efficiency drastically.

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7.2.1

If EP byes are not fitted, the gas flow should be limited to one of the main es during the initial oil firing stage of the pressure raising. The other es should be kept isolated during this period. In this way we can ensure that at least remaining es are not affected by oil vapour. But the E.P. rapping mechanism shall be put in service prior to commencement of oil firing. Anti-condensation heaters of the insulators be taken into service well before boiler light up is initiated. Also it is observed that main cause of poor E.P. performance is high hopper level and this condition is aggravated by moisture when a cold boiler is being lighted up. The hopper heaters, if provided must also be taken in service. Sometimes the hoppers on modern plant are lined up with smooth materials such as fibre glass and ceramics to facilitate the flow. The practice of 'thumping' the hoppers with rods or bars to get the dust flowing should be discouraged as it can damage these linings.

7.3

The EP zones must be taken into service just before coal firing is started in the boiler. The frequency of rapping should be properly adjusted and their operation must be locally checked.

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A.

PRE-START CHECKS, START-UP & LOADING

1.

Pre-Start Checks

1.1

Check that all maintenance permits concerning the boiler pressure parts, flue gas and air side paths are cancelled.

1.2

Check that all the manholes, inspection doors of furnace, flue gas and air path, drum, deaerator, fuel storage tank, C.B.D. tank, I.B.D. tank, fans, mills etc. are tight closed,

1.3

Check that:

1.3.1

Reserve Power and D.C. control system supply is established to 6.6 KV station buses and unit auxiliary buses; 415 volts supply to station service switch gears, unit service switchgear, E.P. switch gear, off-site plant switch gears. Boiler M.C.C., compressor M.C.C., Miscellaneous service M.C.C., soot blower M.C.C., V.D.D.C., F.S.S.S. s etc.

1.3.2

220 V.D.C. board, 220 volts DC supply to control s relay s, emergency lighting, FSSS etc. is established.

1.3.3

110 V.A.C. supply to FSSS s is established.

1.3.4

50 V.D.C. supply to annunciation system is established.

1.4

Check that all the fuses in control and relay are intact.

1.5

Check that electrical supply to the instruments is switched on.

1.6

Check that instrument air compressors are in service and air supply is established for all, Boiler controls (viz secondary air control, Burner tilt control, R.H. Steam temperature Control, burner retract mechanism, milling system pneumatic valve/damper, actuators etc.)

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1.7

Check that station air compressors are in service and air supply is established to Boiler and auxiliaries area and Air heaters air motors.

1.8

Check that clarified water pump (s) is/are in service and clarified water supply for cooling is available for all Boiler auxiliaries.

1.8.1

Check that clarified water booster pump is in service and cooling water supply to sample coolers, air heater lub. oil coolers is available.

1.9

Check that Hydrazine dosing and Phosphate dosing system are ready for taking in service.

1.10

Check that adequate D.M. water is stored in D.M. water tanks.

1.11

Check that Auxiliary steam supply header is charged through interconnection from running Units. (Care should be taken to inform adjacent unit from which steam is being taken prior to charging the header)

1.12

Check that H.S.D. and Heavy oil system are in service on recirculation. Heavy oil temp. is adequate (> 100 0 C).

1.13

Check that Soot Blowers are in retracted position.

1.14

Check that Impulse safety valve is in service condition and that its isolating valve is open.

1.15

Check that Drum, S.H.,R.H., Deaerator, C.B.D. safety valves gags, test plugs have been removed and safety valves are in service condition.

1. 15.1

Check that drum, superheaters and M.S.line vents are open.

1.16

Check that constant load and constant spring hangers of ducting, down comers, M.S.lines, C.R.H.lines, H.R.H.lines and Feed and condensate lines are unlocked and their settings are not disturbed.

1.17

Check that all drives of valves and dampers are in perfect condition and can he operated from remote as well as from local wherever possible/required.

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1.18

Check that Boiler Drum level gauge glasses and remote drum level indicators are in service.

1.19

Check that furnace temperature probe is available.

1.20

Check that all the controls and interlock circuits have been checked and are ready for operation. Check that all protection circuits have been checked and are OK.

1.21

Check that bottom ash hopper and seal trough have been filled and constant over flow is maintained.

1.22

Check that all fly ash hoppers have been evacuated and ash handling water supply is established to all the fly ash hoppers.

1.23

Check that E.I.Ps have been cleaned and are ready for operat ion.

1.24

Check that coal bunker filling has started.

1.25

Check all wind box secondary air dampers and burner tilt for free operation and burner tilt is in horizontal position. Check their operation from remote.

1.26

Check all H.O. guns, warming up guns and ignitors and ignitor spark plug assemblies have been cleaned, inserted back and held tight by coupling bolt.

1.27

Ensure that all guns are in retracted position. Check that fire fighting system is ready.

1.28

Ensure that scraper conveyors and clinker grinders available. Ensure bottom ash trough is filled with water & furnace seal has been established.

2.

Boiler Purging & Lighting Up

2.1

Feed pump is started & Boiler feed line charged.

2.2

Boiler steam & water system is lined up and Boiler is filled up to working level of gauge glass.

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2.3

B.F.P. on Recirculation.

2.4

Boiler air & flue gas system is lined up and start A.P.H.'s. Both the Air heaters should be taken into service if available.

2.5

Take lube oil system of I.D. Fans in service and take oil systems of F.D. fans in service.

2.6

Start one I.D. fan and start one F.D. fan. Start second set of fans if available. (follow the fan start-up procedure as explained earlier).

2.7

Maintain 30% Air flow and -5 to -10mm WCL furnace draft. Airflow shall not be more than 40%.

2.8

Put secondary air damper control system on "Auto" & check that auxiliary air dampers are modulating to maintain 35-40 mm WC Windbox to furnace differential pressure, check fuel air dampers are modulating with aux. air dampers.

2.9

Start E.P. rapping mechanism, check that E.P. insulator heaters were switched on 24 hrs. before Boiler light up.

2.10

Start Scanner Air Fan A/B and start ignitor Air Fan A/B.

2.11

Select Burner tilt control on manual, keep burner tilt in horizontal position and ensure that Heavy oil system is in recircu1ation, Light oil system is charged.

2.12

Check the following for purge start permissives. i)

A.C. & D.C. Power supply is established to F.S.S.S related equipment.

ii)

Drum level is normal

iii)

At least one I.D. fan, one F.D. fan in service.

iv)

Minimum of 30% air flow is established.

v)

Ignitor trip valve is proven closed.

vi)

The light oil trip valve is proven closed.

vii)

The heavy oil trip valve is proven closed.

viii)

All the ignitor valves in all elevations are proven closed.

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ix)

All the warm up and heavy oil nozzle valves at all elevations are proven closed.

x)

All auxiliary air dampers modulating to maintain adequate

wind

box to furnace differential pressure.

2.13

xi)

All purvarizers are off.

xii)

All feeders are off.

xiii)

All hot air shut off gates are fully closed.

xiv)

All cold air dampers are less than 5% Open.

xv)

All elevation flame scanners show NO FLAME,

xvi)

No boiler trip command is present.

Check that atomising air lines for igniters & W.U. oil guns are lined up & charged and make ready each W.U. oil corner individually.

2.14

Start furnace purge by pressing start purge push button at F.S.S.S. console and after 5 minutes check that purge complete light comes on.

2.14.1

Open superheater start up vents and superheater drains.

2.15

Open ignitor trip valve from F.S.S.S. console insert Open P.B. and open light oil trip valve from FSSS console insert open P.B. and select light oil firing from FSSS insert control P.B. for AB elevation.

2.16.1

Establishing light oil elevation permit. i)

D.C. Power available.

ii)

L.O. trip valve proven fully open.

iii)

Air flow between 30% & 40%.

iv)

Burner tilt placed in horizontal position.

v)

No Boiler trip command is persisting.

vi)

Light oil gun is inserted in guide pipe & coupled.

vii)

Local maintenance control switch is placed on "Remote".

viii)

Light oil isolating valve open.

ix)

L.O. Atomising air isolating valves are open.

NOTE: Wherever start up LDO guns are not provided HFO guns are taken into service directly.

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FIG. 2

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FIG. 3

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2.17

Start AB elevation one pair of L.O. guns by depressing pair start P.B. on FSSS insert console, check associated AB elevation at least 3 out of 4 igniters are proven on, check that selected pair of L.O. guns are proven on in time sequence and maintain warm up oil pressure, through pressure regulating valve.

2.18

Start second pair of L.O. guns A.B. elevation by depressing start PB or FSSS console, maintain warm up pressure through regulating valve and check that at least 3 out of 4 L.O. guns are proven on in timed sequence.

2.19

Control firing rate during initial warming up such that boiler starts steaming after 45 minutes and keep C.B.D. control valves fully open during warm up. (As per boiler start up curve. Refer fig. 2 and fig. 3)

2.20

Control flue gas temperature at furnace exit below 538°C by controlling firing rate till adequate flow is established through Reheater. This is done to protect the Reheater. Temperature is measured with the help of furnace temperature probe.

2.21

When boiler starts steaming throttle S.H. vents & drains, Warming up should be slow. Steaming should start after 45 to 50 minutes of lightup.

2.22

When drum pressure reaches 2 Kg/cm2. Close drum vents and outlet header vent and close steam cooled wall extended side outlet header vents.

2.23

Close S.H. Desuperheater link vent valves and close platen S.H. outlet link vent valves.

2.24

Do not close these drain valves fully before rolling the turbine, and check that M.S. line drains are opened (near turbine).

2.25

Throttle start up vent valves to control pressure rise, do not close them fully until turbine is under light load/or HP & LP by system is taken into service (Refer fig.4). Close reheater vents and drains before vaccum raising.

2.26

2

Bring up the Boiler steam parameter to 5 Kg/cm , 195°C.

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3.

Boiler Loading

3.1

Boiler lighted up & main steam pressure & temperatures are 5 Kg/cm &

2

190°C. 3.2

Prepare for Heavy oil firing.

3.3

Check auxiliary steam header is charged through interconnection and check auxiliary steam line F.O. heaters & tracing steam lines are charged.

3.4

Check H.O. system is in service on recirculation before H.O. pressure heaters and check atomising steam lines are charged.

3.5

Take SCAPH corresponding to running F.D. Fan in service & maintain average cold end temperature above acid dew point (90°C).

3.6

Check auxiliary steam is given to feed storage tank heating & deaerator pegging.

3.7

Put H.O. on recirculation through F.O. trip valve F.O. burner headers, check H.O. temperature at burners is 110°C, proceed to take H.O. elevation in service and establish H.O. elevation start permit.

3.8

Depress associated elevation pair start P. B. check H.O. pair is placed in service in programmed sequential order.

3.9

Maintain H.O. burner header pressure above 3 Kg/cm2 and temp. 110 to 130°C, increase H.O. firing rate through H.O. regulating valve and maintain oil/steam DP (Roughly 1 to 1.5 Kg/cm2)

3.10

Warm up oil guns can be taken out once the boiler is warmed up and heavy oil elevation is in service, at least 3 out of 4 H.O. guns at one elevation should be in service.

3.11

Check that vacuum is raised in the condenser by the time M.S. parameters come to 6 Kg/cm2 (ab) and 275°C approx. After raising the vaccum, charge MS lines gradually.

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FIG. 4

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3.12

Take H.P. and L.P. by system in service when Condenser vacuum = 540mm Hg. Main Steam Pr=6 ATA, M.S.Temp.=225°C, ensure B.F.P. and condensate pumps are in service.

3.13

Close start-up vent valves and when flow is established through by system give clearance to start turbine rolling.

3.14

Throttle Main Steam line drain valves, take drum level protection in service. Warm-up M.S. lines, C.R.H., H.R.H. line & transfer lines. Check M.S. 2

Parameters of E.S.V. are 12-14 Kg/cm (g) and 240-260°C. Check M.S. Pipe metal temp. is above 150°C and C.R. pipe metal above 100°C. H.P. transfer pipe line metal temp=150°C and I.P. transfer pipe metal temps=100°C, Boiler Parameters are raised to M.S. Pressure =16 to 18 Kg/cm2 Temperature =250°C-260°C. 3.15

H.P. and L.P. by system is cut out and turbine rolling is started, close M.S. lines drains and C.R.H. line drains to condenser.

3.16

After the machine is synchronised and 5-10 MW load is taken, check furnace temperature probe is retracted automatically when flue gas temp crossess 540°C.

3.17

Start Scraper Conveyor and Slag crusher.

3.18

Maintain average cold end temp. at A.P.H. outlet above acid dew point by controlling steam flow to SCAPH, Check air temperature before and after SCAPH. Check flue gas temp., after A.P.H.

3.19

Check that E.P. rapping mechanism is in service and prepare for charging the fields.

3.20

Inform chemist to check the quality of Boiler water and Feed water as frequently as possible, check phosphate dozing to Boiler water. Maintain Boiler water alkalinity.

3.21

Before increasing the drum pressure ensure that silica content in boiler water is within permissible limits at operating pressure.

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3.22

Prepare for coal firing, start one PA Fan and charge electrostatic precipitators fields.

3.23

Make S.H. spray control system ready and make R.H. spray control system ready.

3.24

Close economiser recirculation valves when continuous flow is established through economiser and close the S.H. header drain, Radiant roof S.H. inlet header drain, side steam cooled wall outlet header drain, Steam cooled wall rear header drain, S.H.S.W.W. front roof inlet header drain and final S.H. header drain.

3.25

Increase firing rate and pick-up 30 MW load. M.S. Pressure 65 Kg/cm2, Temp.430°C R.H.S. Temp. 420°C. Before E.S.V./I.V. take main feed control valve in service and isolate low load valve when low load control valve is 80% open.

3.26

Make ignition energy available to the lowest mill to be taken in service. Start first mill. Preferably lowest and start its R.C. feeder. Put mill air temperature and flow control on auto, check mill outlet temp=65-75°C, air flow = 54 t/hr

3.27

Control drum level and furnace draft carefully.

3.28

Monitor furnace flame stability, increase the feeder speed upto 50% of rated and check ash handling system is taken in service. Check mill differential pressure is less than 200mm, switch on E.P. hopper heaters.

3.29

Increase the main steam/R.H. steam parameter as per cold start curve, maintain S.H. steam temp. control by spray water control and maintain R.H. steam temperature by burner tilt.

3.30

Increase the load on generator as Boiler output increases and maintain boiler pressure.

3.31

Start second mill when first mill is loaded to 80%, start associated mill feeder, when mill is warmed up.

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3.32

Increase the feeder speed. Equalise the loading on both the feeders, boiler parameters: M.S. Pressure = 82Kg/cm2 M.S. Temp = 475°C Load = 60MW.

3.33

When load on unit is 70MW check H.P. heaters are taken in service. M.S. pressure 105 Kg/cm2 (g) At boiler outlet. Check heater drip pump cuts in automatically at around 70MW load.

3.34

Start 2nd I.D. fan at 60 MW load and equalise loading on both I.D. fans.

3.35

Start 2nd F.D. Fan and equalise loading on both F.D. Fans.

3.36

Maintain necessary total air flow and furnace draft, check stack exhaust colour for proper combustion and take SCAPH corresponding to second F.D. Fan in service if necessary, Check O2 and CO, CO 2 content in flue gas. (Refer fig. 5).

3.37

Check that auxiliary air and fuel air dampers are modulating and necessary windbox to furnace differential is maintained, at 30% load furnace to windbox differential should be 40mm wcl.

3.38

Start 2nd P.A. Fan and equalise loading on both P.A, Fans. Put P.A. pressure control on Auto, maintain P.A. Pressure above 600 mm Wcl.

3.39

Check that 2nd condensate pumps and 2nd boiler feed pump are started, before starting standby BFP it must be warmed up.

3.40

Check that deaerator pressure is increased to

6Kg/cm2

gauge,

put

deaerator pressure control on auto. 3.41

Inform laboratory to check Boiler and Feed water quality, for intermittent phosphate dozing if situation demands.

3.42

Take 3rd pulverizer and its feeder in service when loading on running pulverizers exceeds 80% and equalise loading on all the 3 pulverizers.

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3.43

Increase load on the generator and simultaneously increase Boiler firing rate 2

and boiler pressure 120 Kg/cm M.S. Temp 530°C Load 120MW, put M.S. & R.H. Steam temp, control system on Auto. 3.44

Put B.F.P's Scoop tube control on auto and put Main feed control valve on Auto position. Check that drum level is maintained by the controller.

3.45

Put both I.D. Fans and inlet vane control i.e. Furnace Draft control on auto, check that -10mm furnace draft is maintained.

3.46

Put total air flow control on auto. F.D. Fan impeller vanes control, check 02, CO and C0 2 content in flue gas at APH inlet by Orsat. Ensure that sufficient excess air is maintained.

3.47

When load on running mill is above 80%, take 4th mill and its feeder in service and equalise loading on all 4 mills.

3.48

Flame H.O. guns can be removed once boiler loading is above 60% and more than 2 mills are in service at 50% loading and at least two adjacent mills are in service.

3.49

SCAPH's can be cut out when flue gas outlet temps. increases to 130°C or when H.O. is removed. Put Thermal load control on "Auto".

3.50

Increase load on generator. Check that Thermal load control maintains Boiler Parameter by controlling firing rate, check M.S. & R.H. steam and tube metal temperature.

3.51

Increase load on generator to 210 MW, check the Boiler Parameters and drum pressure 145 Kg/cm2 M.S. Pressure 138 Kg/cm2 (ab) M.S. Temp. 540°C + 5°C R.H. Steam Pressure 24Kg/cm2 (ab) R.H. Steam Temp. 540 + 5°C Feed Water temperature 245°C.

3.52

Check M.S. temperature low trip interlock comes in service when M.S. temperature goes above 520°C.

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B. 1.

NORMAL SHUT DOWN TO COLD Suitable for shut downs of medium duration when Boiler or Turbine inspection is planned when Unit is operating at 210 MW with combustion control, fuel control, total air control, Feed water control, steam temperature controls Furnace draft and all other control on 'Auto'

1.1

Take "Combustion control" on "Manual" mode, take "M.S. Temperature low" trip protection out and isolate initial steam pressure unloading gear.

1.2

Gradually reduce load on the unit reducing firing rate. MS/HRH steam temperature and MS pressure shall be reduced at the rates permitted by the turbine but not exceeding the rate of saturated steam temp drip of 83°C/hr. Rate of load drop may be about 2 MW/min. Carefully monitor turbine conditions and adjust the load, temp., pressure drop rates such that HP/IP rotor

differential

expansion,

vibration,

eccentricity,

shell

differential

temperatures, turbine cylinder top/bottom metal temps, Left/Right cylinder flange temp. diff. are within limits. 1.3

Load Reduced to 160 MW, take HP heaters out of service.

1.4

Load Reduced to 150 MW Approximate parameters at Turbine inlet are: M.S. pressure=120 Kg/cm2 (g), M.S. Temp=520°C, R.H.S., temp=520°C.

1.5

While reducing load, check that following conditions are maintained.

1.5.1

Total air flow is reduced in proportion with load upto 30% load.

1.5.2

Check drum level is maintained normal on Auto.

1.5.3

Check S.H. & R.H. steam temperatures are maintained at set points. Furnace draft is maintained.

1.5.4

Check the boiler expansion/contraction movements as the load is reduced.

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24

1.6

When the load on mills is reduced to 40%, prepare to take upper most mill out reduce the feeder speed to minimum.

1.7

Take upper elevation oil guns in service, simultaneous with this transfer load on other mills in service. Stop the upper most feeder and take the upper mill out of service after cooling it down to 44°C and emptying it out completely.

1.8

When load on unit is reduced to 100 MW. M.S. Temp.=510°C M.S. Pr = 112 2

Kg/cm (g) H.R.H.S. Temp.=510°C, check that deaerator steam supply is switched over from 2nd extraction to Aux. steam header. 1.9

At 100-90 MW take out one boiler feed pump from service. Check that full load is smoothly transferred on running B.F.P. before stopping the pump, before stopping B.F.P. take the standby B.F. P&S on working from Auto. Ensure that auto standby B.F.P. does not start on stopping of running BFP through interlocks.

1.10

Continue reducing firing rate steam temperature and pressure alongwith drop in load. (Refer fig.4) .

1.11

When the load on mills is reduced to 40% take next upper elevation oil guns in service and take heavy oil guns associated with remote elevation mill in service.

1.12

Prepare to take the next upper elevation mill out. Reduce feeder speed to minimum & stop feeder. Stop the mill after cooling down to 44°C and completely evacuating it, see that load is transferred on the running mills.

1.13

Take Heavy oil guns at lower elevation in service and take out next higher mill from service when loading on mills is reduced to 40%.

1.14

Take M.S. and R.H. steam temp, control on Hand and continue reducing firing rate steam pressure and temp. with reduction in load.

1.15

At 70 MW load M.S.Temp.=490°C R.H. Steam Temp=490°C M.S. Pressure 2

=105Kg/cm .

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25

1.16

Take drum level control on manual & maintain drum level.

1.17

Stop one PA Fan after transferring full load on running P.A. Fan, stop lub. oil pumps of tripped P.A. Fan motor and fan bearings after oil bearing temperature is reduced.

1.18

Stop one F.D. Fan corresponding to P.A. tripped. Check furnace draft and air flow, before stopping F.D. Fan increase load on other F.D. Fan and reduce load on this fan to minimum.

1.19

Stop one I.D. Fan corresponding to tripped F.D. Fan check furnace draft, transfer load from this I.D. Fan to other and completely unload this I.D. Fan before tripping it.

1.20

Switch off supply to the Electrostatic precipitators associated with tripped I.D. Fan, carry out soot blowing of complete boiler.

1.21

Unit load reduced to 30% Maintain 30% air flow at all loads below 30% check that secondary air dampers set point is ramped to maintain windbox to furnace differential pressure of 35-40 mm Wcl.

1.22

Firing rate is reduced further and when load on mill is reduced to 40% reduce, feeder speed to minimum stop the feeder. Cool down mill to 44°C & evacuate it completely and shut it down.

1.23

When load is reduced to 40 MW take low load Feed Control Valve in service and isolate main Feed control valve, open low load control valve of feed control system.

1.24

Switch off supply to field of Electro-static precipitator.

1.25

Unit at 25-30 MW with H.O. firing and change over auxiliary electrical supply from U.A.Ts to station transformer.

1.26

Stop P.A. Fan, check that seal air fan trips on interlock. Check the P.A. damper operation, Close sealing air valves to mills from station air system.

© PMI, NTPC

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1.27

Reduce load on unit to 5-7 MW M.S. Pressure Boiler outlet 90 Kg/cm2 (g) M.S. Temp. Boiler outlet 465°C R.H. Steam Temp 465°C.

1.28

Charge Auxiliary steam header from running units through interconnection, isolate Auxiliary P.R.D.S. unit.

1.29

Trip the unit through M.F.T. Push Buttons on F.S.S.S. console/or Through Protection, When boiler is to be tripped, trip it through protection. Maintain log of protection used each time is stopped. Use different protections each time so that all are checked and check that H.P. cylinder evacuation valves Open.

1.30

Check that Boiler fire is completely out, check that all the flame scanners sense no flame & check boiler actually from peep holes & ensure that fire is completely out.

1.31

Maintain 30% air flow and purge the boiler for at least five minutes, check that turbine coasts down safely and see bearing lubricative system.

1.32

Check that all the feeders and mills are off, break the vaccum when turbine speed comes to zero, put turbine roter on barring geat Check that F.C.N.R. Vs in Extraction lines are closed.

1.33

Individual burner H.O., M.V. oil, Atomising air and steam nozzle valves and Ignitors valves (air/oil) are closed.

1.34

Check that Attemperation SH & RH isolating valve and its by valve are closed, close isolating valves of SH. and Reheater spray control valves.

1.35

Open S.H. Start-up vent isolating valves partially open S.H. start-up vents reduce pressure, rate of pressure drop must not exceed the limits specified to limit Saturation temp. drop rate to less than 83°C.

1.36

Open Reheater vents and close C.B.D. valves.

1.37

Close Boiler Main steam stop valves and their by valves.

1.38

Open M.S. line drains valves open C.R.H. & H.R.H. line drains.

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1.39

Shutdown - H.O. System.

1.40

Top up the drum level upto + 180 mm, stop Boiler feed pump.

1.41

Stop Hydrazine dozing pumps, stop phosphate dozing pumps if it is in service.

1.42

Cut off deaerator Pegging steam supply by closing the valves.

1.43

Do not stop A.P. Heaters till Flue gas temp. at A.P.H. inlet is less than 205°C, and air Flow through furnace shall be controlled to effect the desired cooling rate and it can be controlled by :(1.) Opening S.H.H. vents (2.) Air Flow through boiler.

1.44

Boiler is to be forced cooled fast after shut down, keep I.D. Fan and F.D. Fan in service. Regulate airflow to effect desired rate of cooling, open starting vent valves.

1.45

Bring up drum level to +180mm when it drops to -180, start Boiler Feed pump for topping up the level. Stop Boiler Feed pump afterwards.

1.46

Open vents and drains of S.H. at low pressure (2 to 3 Kg/cm2 g) At 1.8 kg/cm drum pressure. Open drum vents.

1.47

Stop F.D. Fan and I.D. Fans when flue gas temperature at A.P.H. inlet is reduced to below 205°C and boiler is cooled. Check that A.P.H. do not stop on interlock take de-interlocking switch is on "de-interlock" position before stopping F.D./I.D. Fan.

1.48

If required, stop Air preheaters otherwise keep them rotating, check that A.P.H's lube oil pumps stop on interlock when oil temp, goes below 40 C.

1.49

When Boiler water temperature goes below 94°C, drain the Boiler or preserve it according to the circumstances/instructions.

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C. 1.

UNIT SHUT DOWN TO HOT STANDBY In this case it is presumed that the Boiler is to be shut down for a relatively short period of time and existing pressure and temperature conditions are to be maintained substantially to facilitate quick hot restart without developing undue thermal stresses. Before tripping the unit turbine cylinders E.S.V's, IVs body metal temperatures are reduced to the extent that after shut down time i.e. at the time of re-rolling the turbine, exact matching parameters are obtained using 30% capacity H.P. and L.P. by system. The sequential operation procedure is similar to that of "Shutdown to cold" except the different of load drop and temperature and pressure reduction rates.

1.1

If it is expected that unit will be restarted in a very short time in which turbine metal temperatures will not decrease appreciably, it may be desired to cool the turbine regulating stage metal temp. to below 427°C by reducing the steam temperature and pressure.

1.2

Initially load may be reduced at the rate of 3 MW/min. at rated steam parameters upto load of 140/120 MW.

1.3

Subsequent load reduction alongwith temperature and pressure drops should be decided by turbine limitations.

1.4

During Boiler M.S. pressure drop the saturated steam temperature drop rate shall not be more than 83°C/hr.

1.5

When the desired pressure at which boiler is to be held is reached and load on machine is reduced and then unit is tripped.

1.6

After tripping the unit Boiler may be boxed up by keeping all S.H. drains and vents, Boiler stop valves closed.

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Reheater vents (if condenser vacuum is broken) and drains are kept open. 1.7

After stopping I.D. Fan and F.D. Fan, close all flue gas dampers secondary air dampers and windbox dampers.

1.8

A.P.M. can be stopped when flue gas temperature at A.P.H. inlet is below 205°C. But it is preferred to keep A.P.H. rotating even below 205°C temperature (Flue gas inlet to A.H.)

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D.

ROUTINE CHECKS

1.

Checking Procedure

1.1

A round of the complete boiler and auxiliaries area is to be taken for checking the following at least once in a shift to ensure the healthiness of the boiler and Auxiliaries.

1.1.1

Inspect the furnace flame condition and stability.

1.1.2

Inspect the complete Boiler pressure parts for any leakage.

1.1.3

Inspect the flue gas and Air paths for any leakage through ducting and manholes etc.

1.1.4

Inspect the running auxiliaries like F.D. Fan, I.D. Fan, P.A. Fans, mills, A.P.H. etc. for any abnormal sound, high vibration, high lub oil/ bearing temperature, lub. oil pressures etc.

1.1.5

Check the unit operating parameters and compare with the predicated readings and previous records. Any deviation should be reasoned out and corrected.

1.2

Drum gauges glasses may be blown once a day and compare Drum level readings of local gauge glass remote level gauge glass and U.C.B. instruments (to be done by charge hand/18m Boiler operator).

1.3

Compare local instrument reading with remote U.C.B. mounted instrument once a day and if any appreciable discrepancy is observed bring it to the notice of C&I division.

1.4

Check the steam, boiler water, feed water and make up water quality and ensure that it is maintained in the recommended regime.

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1.5

Check the steam, boiler water, feed water and make up water quality and ensure that it is maintained in the recommended regime.

1.6

Check that a continuous flow of sampling water is maintained through sample cooler. Also check for sufficient flow of cooling water through sample cooler.

1.7

Get fuel combustion completeness checked once a shift by analysing flue gas by Orsat Apparatus. Check O 2%, CO%, CO 2%. Take corrective action for excess air adjustment.

1.8

Check stack emission visually. A white smoke indicates high excess air and black smoke indicates insufficient air flow, both should be avoided.

1.9

Check pressure drop & temperature along the flue gas path primary & secondary air path. Compare with past record, reason out any abnormal deviation and take corrective action.

1.10

Check feed water temperature before and after economizer.

1.11

Check R.H. & S.H. tube metal temperature and ensure that no overheating of tubes is existing.

1.12

Check steam temperature at various stages of S.H. & compare with predicated values.

1.13

Carry out soot blowing operation at regular intervals or as and when found necessary.

1.14

Carry out soot blowing of A.P.H. elements at least once in a shift.

1.15

Get ash samples Bottom/Fly ash analysed once in a day for Carbon content. Accordingly classifier adjustment must be done.

1.16

Check the fineness of pulversed coal from each mill once a day. Carry out necessary adjustments.

1.17

Get the raw coal analysis done once a day or wherever necessary.

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1.18

Check for any choking in bunker if any reduction of coal flow from R.C. bunkers is observed, take corrective action.

1.19

Check individual pulvariser for coal air temperature, high differential pressure across bowl, air flow, classifier setting, abnormal sound, high vibration and oil temperature etc.

1.20

Check raw coal bunker levels are normal while unit is in operation and empty out bunkers if unit is planned to be shut down for a few days or more.

1.21

Check the continuous and satisfactory operation of slag scraper conveyor, slag crusher.

1.22

Check for continuous and satisfactory operation of fly ash system.

1.22.1

Check electrostatic precipitator operation. (Field voltage, current, spark rate).

1.22.2

Check good fluidity of fly ash is maintained by hopper heaters.

1.22.3

Check rapping mechanism operation.

1.22.4

Check that reheater temperature is controlled by burner tilt and reheater attemperation is avoided as far as possible.

1.23

Check that igniters spark plugs are kept cleaned for immediate starting whenever required.

1.24

Check that flame scanner show constant "Flame on" condition. In case of flickering "Flame on" and "Flame off" light check furnace flame condition, take oil .

1.25

Check that pu1verisers are loaded to 80% capacity with reserve 20% capacity for handling emergency conditions.

1.26

Check that loading of parallel running I.D. Fans, or F.D. Fan or P.A. Fans are equal as far as possible.

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1.27

Check H.O. temperature, burner header pressure, Atomising steam pressure & temperature are maintained normal.

1.28

Check W.U. oil headers pressure and Atomising air header pressure are maintained normal

1.29

The following Auxiliaries should be changed over to stand-by equipments once in a week.

1.29.1

Seal air fan.

1.29.2

Ignitor air fan.

1.29.3

Hydrazine dozing pump.

1.29.4

Phosphate dozing pump.

1.29.5

Coal mills (if all the mills are available).

1.29.6

Lub. oil pumps of ID, FD & PA Fans.

1.30

Check that bottom ash hopper sealing is maintained & water overflows through seal trough.

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34

E.

EMERGENCY OPERATIONS

Given in this section are probable reasons for major emergency situations in Boiler & Aux. Areas and suggested actions.

1.

1.1

HIGH FURNACE PRESSURE Probable Reasons

Action to be taken

One I.D. Fan tripped or Mal-operation

Take running I.D. Fans control on

of control vanes of I.D./F.D./P.A. Fans

manual & increase for loading. Check

or closing of damper

the cause of I.D. fan tripping and try to restart it if everything is normal. Check gas dampers indication & Draft read ing along Flue gas path. If some damper is closed try to open that damper.

1.2

Unstable furnace flame conditions.

Take F.D./P.A. fan control on manual.

Sudden starting of coal mill. Low

Check con trol damper operation. Adjust

windbox pressure (under normal F.D.

air flow. Check air for correct flow.

fans loading conditions), improve air

Check Combustion regime openings of

distri bution at elevations or too high

Auxiliary air and fuel air dampers,

fuel air. fuel air.

windbox pressure. See cold air and hot air dampers. Watch Furnace flame. Trip Boiler if flame is very much unstable. Purge

out

explosive

mixture

by

maintaining high air f1ow. 1.3

Un-equal burner tilts at corners or

Check Burner tilt at all corners is equal.

Burner

Adjust Burner tilt between +10 to -10 and check control air pressure

1.4

Fouling in Air heater, air heater

See air-preheaters are rotating. Restart

tripped.

tripped air preheater and do A.H. soot blowing

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1.5

1.6

Furnace water seal bro ken, E.P. or

Check Furnace seal, water flow through

flue gas path manhole opened.

seal through overflow. Re-establish seal

Water wall tube rupture/leakage.

Stop the boiler in case of tube leakage as soon as possible.

2.

FURNACE PRESSURE LOW

2.1

I.D. Fan auto control Failure.

Take I.D. Fans control on manual & reduce load on I.D. Fans.

2.2

2.3

I.D. Fan vane control mechanism

Check I.D. Fan control mechanism or

Failure causing vanes to open wide.

proper Functioning.

Sudden decrease in air input or

Check air flow, correct if necessary.

tripping of one F. D. fan.

After checking restart I .U. Fan if it had tripped.

2.4

Sudden tripping of one or more mills

Control

the

Furnace

or chok ing of mi1s/raw coal Feeder

adjusting

pipe.

Simultaneously try to start stand by mill.

I.D.

pressure Fan

by

vanes.

Remove the choking of affected mill/raw coal feed pipe. 2.5

Partial flame failure

Take the oil gun into service to establish flame at that locations/ corner.

2.6

Accidental closing of secondary air

See the proper functioning of secondary

path dampers or Auxiliary/ Fuel air

air path damper.

dampers.

3.

DRUM LEVEL LOW

3.1

Mal-operation of Feed Auto Control or

Take feed control valve on hand and

Feed Regulator or scoop auto.

increase feeding rate. Take scoop tube control on hand and increase scoop

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tube position. Check that F.W. flow through each pump does not exceed its capacity. Check feed water control valve and scoop tube control 1inkages. 3.2

3.3

Tripping of one of working feed pump

Start reserve feed pump on tripping of

(standby pump does not start)

running feed pump. If auto starting fails.

Sudden Reduction of load.

Try to increase the load if not possible reduce firing rate accordingly to control drum pressure.

3.4

Sudden increase in firing rate, e.g.

Reduce firing rate by suitably adjusting

starting of mills having sufficient coal

the feeding rate of running mills.

left before previous stopping. 3.5

lube repture/puncture of low point

Check water flow and compare with

drain valves or Emergency drum drain

previous; feeding rate and steam flow.

valve

High feed flow indication tube failure. Inspect water wall and economiser or any tube leakage. If tube leakage1 is observed stop the boiler as soon as possible.

3.6

Inadvertant opening of low point drain

Check drum drains and low point drain

valves or Emergency drum drain

for tight closing.

valve. Note: If drum level goes below gauge glass and low drum level trip protection fails, trip Boiler at once.

4.

HIGH DRUM LEVEL

4.1

Ma1-operation of feed water control.

Take feed control valve on manual and reduce the feeding rate.

4.3

Sudden decrease in firing rate e.g. tri-

© PMI, NTPC

Increase feeding rate of running mills.

37

pping of the running mills. 4.4

B.F.P. Scoop tube position suddenly

Check differential pressure across feed

increased.

control valve and maintain 5 Kg/cm by

2

adjusting scoop tube position.

5

FLAME FAILURE AT AN ELEVATION

5.1

Closing of trip valves on H.O. , W.U.

Do not attempt to introduce ignitors or

Oil/ Ignitor (Causing loss of ignition

oil guns at elevation where "No flame"

energy) Where F.O. is being

condition persist.

used as fuel or when only oil is being used 5.2

Sudden

decrease

of

mill

feeder

speeds to minimum.

Trip out the coal mills of feeding elevation where "No flame” condition is persisting. Allow sometime for purging then introduce oil adjacent to working mills until furnace flame is stabilised.

5.3

Too low or too high windbox pressure

Check that secondary air windbox

causing unstable combustion.

dampers are modulating to maintain about

80mm

windbox

to

furnace

differential pressure. 5.4

Water wall tube failure

Check furnace for tube failure.

5.5

Malfunction of flame scanners due to

If

supply failure or scanner air failure,

"No Flame" trip the boiler manually.

two

elevations

scanners

show

slag or soot on scanner lenses etc. 5.6

Burner

tilt

mechanism

negative

Check Burner tilt keep it between +10°.

extreme due to air failure to power cylinders.

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5.7

Rapid load changes without adjusting air

flow

leading

to

Check furnace flame condition.

improper

combustion.

6.

ONE FAN TRIPS (OT HER IN SERVICE) It is presumed that I .D./F.D./P.A. for de-interlocking switches are on "Interlock" position.

6.1

Fan Bearing temperature high.

1.

Take

draft

control

on

manual

increase the loading increase the and/or

loading on running Fan and maintain furnace draft.

6.2

Fan motor Bearing temperature high,

2. Check corresponding Fan is tripped

and/or 6.3

through interlock.

Lube oil pressure for motor bearings

3.

low.

manual and maintain correct air and/or

6.4

Corresponding

Take secondary air flow control on

Air

flow. heater

tripped

4. Cut in oil Burner adja cent to working

(provided de-interlocking switch is on

mills.

'Interlock' position) and / or 6.5

Motor protection operated.

5.

Check drum level is controlled on auto if necessary, take drum level control on manual arid maintain level.

6.

Check pulverizer in excess of 3 are tripped starting from bottom.

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7.

Check that

the

load

on

the

generator has reduced to 100 to 120

MW

(Partial

load

relay

energised). 8.

Check

that

interconnecting

dampers on air and flue gas side open

and

correctly

tripped,

fans

isolated

are

through

interlocks. 9.

Check windbox pressure left and right

is

maintained

normal

(about 75 mm Wcl.) 10.

Maintain steam temperature.

11.

Check furnace flame condition.

12.

Check that tripped pulverizers are correctly isolated (hot air gates close, cold air dampers come to minimum).

13.

Investigate

the

cause

of

trip.

Correct it and restart the tripped Fan.

7.

ONE FEEDER TRIPS

7.1

energy is removed within 3 minutes of feeder starting. and/or

© PMI, NTPC

1.

Check that hot air gate closes & cold

air damper opens full if

pulveriser is running.

40

7.2

No coal flow alar m comes & low

2.

current relay picks up simultaneously.

Clear the mill or the coal before stopping it.

(Feeder shear pin given way) and/or Mill trips,

3. and/or

7.3

Feeder motor supply fails

Stop the pulverizer if feeder cannot be restarted immediately.

4. 5.

Check that running mills share the load if thermal load is on auto.

5.

Reduce the load on generator and maintain steam parameters.

6.

If 3 mills at less than 50% feeder speed or 2 mills are left in service, out in oil gun, adjacent to working mills.

7. 8.

Check Furnace draft, air flow and drum level are normal.

9. 10. Check flame is stable and scanners sense “Flame on". 11. 12. Check that associated elevation fuel air damper close and windbox pessure is maintained 70 mm WC.

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8.

ONE MILL TRIPS

8.1

Mill discharge valves are closed

1.

and/or

Check that running mills share the load if thermal load control of mills are on auto.

Loss of elevation D.C. supply for more

2.

than 2 secs.

Reduce

the

generator

load

if

pressure starts dropping.

and/or ignition energy is removed

3. Start reserve mill and take load.

with minutes of feeder starting. and/or Motor protection operates.

2.

and/or One P.A. Fan trips (mill in excess of 3

Check furnace draft is maintained normal.

3.

will trip starting from bottom).

Check the

correct air flow

is

maintained. 4.

Check that drum level is maintained normal.

5.

Check that tripped mill is isolated (Hot air gate closed, cold air damper minimum open, Feeder tripped.

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9.

COAL HANGUP IN MILL Choking of coal at inlet to mill

9.1

High moisture in coal

1.

and/or Too much fines in coal with moisture.

& low current" protection. 2. Check mill outlet temperature is less

and/or Foreign material at R . C . feeder inlet.

Check feeder trip on "No coal flow

than 85°C. 3.

and/or

Check Mill hot air gate closes on mill

outlet

temperature

high

protection. Close hot air gate and check mill. Big lump of coal.

Cold air damper opens full. 4.

Check the flame condition at the sick mill elevation.

5.

Trip the sick mill after clearing it of coal.

6.

Increase the load on running mills if Thermal load control is on manual.

7.

Start reserve mill.

8.

Maintain

steam

pressure

and

temperature by reducing load. 9.

Check that furnace draft and air flows are normal.

10. If 3 mills (or less) are in service with feeder speed below 50% take oil elevation adjacent to running mills in service.

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10.

WATER MILL TUBE LEAKAGE Starved water wall s due to very low

1.

Compare Feed Water flow and

drum level.

steam

and/or

magnitude of tube leakage.

Sustained

flame

impingement

on

2.

water wall tubes.

flow

to

assess

the

Maintain drum level by increasing feed water flow.

and/or Blocked

tube,

scaling

of

tube,

3.

resulting in overheating of tube metal,

Inspect

the

furnace

for

tube

leakage.

pitting, corrosion of tubes. and/or Soot

blower

steam

impingement

4.

If the tube leakage is minute then

(wet steam impingement or direct

take the unit out as a planned

impingement of steam).

shutdown to cold.

and/or Circulation affected due to opening

5.

of low point drains.

If tube leakage is heavy and it is likely to damage other tubes or likely to disturb the flame stability trip out the unit.

6.

Keep

close

watch in

furnace

f1ame. 7.

As the load is being reduced try to locate the burst tube (s) as it would help in early repair.

8.

Check econoimiser hoppers for water leakage steam noise etc. every shift.

9.

Check

that

furnace

draft

maintained normal.

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is

11.

REHEATER/SUPF RHEATER/ ECONOMISER TUBE FAILURE

11.1

Substained high metal temperatures due to waterwall Slagging or forcing boiler at the time

1.

As soon as leakage is detected

of hot restart.

start load reduction and trip cut the

and/or

boiler at the earliest possible time.

Erosion on tubes due to high excess

2.

Try

to

located

air, high ash content in coal dislocated

manholes

before

tubes, soot blowing.

depressurised.

leak

through

Boiler

is

and/or Blocked tubes causing overheating. and/or Salt deposition due to high water level in drum, poor quality of water. and/or Inadequate

flow

due

to

open

superheater, reheater drain, and/or Fire side corrosion of tubes. and/or Economiser tube can fail due to over heating if concentra tion of Fe, Cu is more in Feed water. Steaming in economiser

occurs

causing

salt

deposition and harming.

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1. 1.1

PUMPS In a power station there are large number of pumps doing certain specific job assigned to them. Depending upon the duty a pump is expected to perform, different types of pumps are selected for that particular operation. The operation staff must know the correct operating procedures for each pump for any maloperation of pump leading to its shut down may cause reduction in power generation. This is especially more important in case of high pressure boiler feed pumps which is a very expensive machine. It requires careful and skillful operation which is possible only if the operating engineer is fully familiar with the subsystems of the pump and their operation procedure along with the main pump. From the operating parameters, the operation engineer must be able to deduce the possible cause of maloperation and take timely corrective steps so as to avoid damage to the pump. Each pump manufacturer supplies the pump operation instructions which must be followed

carefully.

A typical boiler feed pump operation procedure is explained below. The operation engineer mu st understand each step and the logic involved to carry-out and this step. BOILER FEED PUMP (200 KHI) 1.1

When all the feed pumps are in stopped condition and one feed pump is to be started carry out the following checks.

1.2

Local Checks

1.2.1

No maintenance staff in working on the pump.

1.2.2

All the control instruments and gauges are in proper place. All root valves for different gauges are in open condition.

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1.2.3

Cooling water for booster pump bearing cooling as well as gland sealing water supply is O.K.

1.2.4

Check availability of compressed air for pneumatically operated valves.

1.2.5

Check that Deaerator level is normal. Make local check and confirm by draining the gauge glass and recharging it.

1.2.6

Check that oil level in lub. oil tank is normal.

1.2.7

Take out EPB of auxiliary lub. oil pump. Confirm that it starts and develops required lub. oil pressure. The pressure of oil before journal bearing should be 0.8 to 1 Kg/cm2 and 0.5 Kg/cm2 before the thrust bearing. Check lub. oil flow through drain line is normal.

1.2.8

Check that both lub. oil and working oil coolers are charged from water as well as oil side.

1.2.9

Check lub. oil level of booster pump is normal.

1.2.10

Check paver operated recirculation valve is closed and manual operated valve at Deaerator is open.

1.2.11

Check that manual valve at deaerator on balancing chamber leak off line is open.

1.2.12

Check BFP discharge valve & its by valve is closed.

1.2.13

Check that drain valves are closed.

1.2.14

Charge the feed line after opening vents provided, upto feed regulating station and then close all the vent lines.

1.2.15

Charge seal water cooler and stiffing box and LP cover cooling lines.

1.2.16

Charge feed pump motor cooler.

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1.2.17

Check scoop tube is in minimum position.

1.2.18

Check that the difference of temperature between pump body metal and feed water temperature is less than 30°C.

1.2.19

Take out EPB of main pump and give clearance to UCB for starting.

1.3

UCB Checks

1.3.1

Check no PTW is pending.

1.3.2

Check feed pump gauges in UCB are in proper working order.

1.3.3

Check all remote operated valves have been given power supply & confirm their proper operation with local operator.

1.3.4

Check D/A level is normal. (Also confirm locally)

1.3.5

Check lub. oil pressure is O.K.

1.3.6

Check all the protection and interlocks of the pump have been checked and are O.K.

1.3.7

Check feed line has been properly lined up.

1.3.8

Check the valve indications (OPEN/CLOSE) are O.K.

1.3.9

Get electrical supply for the pump.

1.3.10

Check all the flag relay provided for the pump are reset.

1.3.11

Check that the boiler requires feed water.

1.3.12

Announce for feed pump starting &. ask local operator to be near pump.

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1.4

START the feed pump

1.4.1

Check starting current and time.

1.4.2

Check that recirculation valve opens and proper suction flow in maintained.

1.4.3

Check electrically operated cooling water valve opens & proper cooling water flow is established.

1.4.4

Check warm up valve has closed.

1.4.5

Check auxiliary 1ub. oil pump has stopped.

1.4.6

Check feed pump vibration are normal (local check)

1.4.7

Check balancing leak off’ chamber pressure is normal.

1.4.8

Check bearing temperatures of main pump, motor and hydraulic coupling bearings are normal.

1.4.9

Check the lub. oil drain flow again.

1.4.10

Open the feed pump discharge valve and take the flow as per requirement in boiler.

1.4.11

Check recirculation valve operation after sufficient discharge flow is established.

1. 5

Routine Checks

1.5.1

For a pump which is in continuous service, check the following every hour:

1.5.2

In no case bearing drain oil temperature should be above 70°C. -

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Check oil cooler inlet and outlet valves are open fully.

49

-

Check whether adequate cooling water flow is there. If temperature is still going high inform U.C.B.

1.5.3

Motor hot air cooler temperature - Normal working temperature is around 60°C. If it goes beyond this, inform UCB (Release air lock in the water side of cooler through the vent cock). If temperature goes beyond 75°C-80°C, stop the pump and check coolers. 2

1.5.4

Bearing oil pressure at LCB - constant at 1.0 Kg/cm .

1.5.5

Suction pressure: Around 10 Kg/cm depending on D/A pressure but should

2

not go below 6 Kg/cm2 and should not be fluctuating too much. 1.5.6

2

Discharge pressure - Around 170 Kg/cm for normal working. It should not also be fluctuating.

1.5.7

B.C.L. pressure - should be 3 to 4 Kg/cm2 above suction pressure. In no case the difference of pressure between suction branch and B.C.L. should exceed 5 Kg/cm2.

1.5.8

Feed water flow through the pump at any instant should not be less than 200 T/hr, if it is less open the recirculation valve informing UCB and see that the flow rises.

1.5.9

Feed water temperature at discharge of pump Around 170°C at normal working conditions.

1.5.1.0

Bearing oil flow - should be continuous without foaming at the sight glasses of individual bearings.

1.5.1.1

Lubrication oil pressure before and after the filter, the difference should not be above 0.5 Kg/cm2 . The discharge pressure for all the bearings of boiler feed pump and hydraulic coupling should be about 1.0 Kg/cm2 excepting the thrust hearing for which it should be about 0.5 Kg/cm2 .

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1.5.12

Check that the booster pump runs smoothly and there is no leakage of water from its glands. Check that there is adequate flow of gland cooling water.

1.5.13

Bearing oil temperature of the booster pump should be checked for normal and should be within the limit (approx. 60°C).

1.5.14

Oil temperature at outlet of cooler around 85°C. If the temperature is high, check that adequate water is flowing through the cooler and if not, inform UCB.

1.5.15

Check for the oil level in the oil tank of the hydraulic coupling. It should be normal. If not, proper grade of oil is to be topped up. If the level is falling continuously it indicates oil leakage in the system/oil seal failure of rotor bearings. Inform UCB immediately.

1.5.16

Check seal water temperature - to be around 65°C -70°C.

1.5.17

The lub. oil is to be tested for mechanical impurity, acidity and moisture content at least once in a week or as per requirement.

1.5.18

See that the stand-by feed pump is not idle for more than a fortnight.

1.6

Normal Shutting Down Of Pump

1.6.1

Open recirculation valve (to avoid damage to mech. seal) and then close the discharge valve of the pump to be stopped.

1.6.2

Get scoop tube setting at minimum position.

1.6.3

Now switch-off the Boiler reed pump.

1.6.4

Check that motor air cooler water side electrically operated valve closes automatically after stopping the pump. If not close it from UCB.

1.6.5

Check that auxiliary lubrciating oil pump has started.

1.6.6

Check that B.F.P. warm-up line pneumatically operated valve has opened.

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1.6.7

However in case of extreme emergency feed pump can be stopped with discharge valve open.

1.7

Feed Heaters Regenerative feed heating improves the cycle efficiency substatically. Any feed heater out of service would mean drop in efficiency which in turn would raise the cost of generation. If all the heater are in service then also, we would be operating at lesser efficiency unless feed heater performance is optimum. In operating feed heating plant the effort in to obtain maximum amount of work from the bled steam and minimise the loss of work owing to bleeding. In practice this means keeping feed outlet temperature from each heater as high as possible. This can be monitored by keeping an accurate record of the terminal temperature difference of each heater. The terminal temperature difference in the difference in temperature between the condensing bled stream and outgoing feed water. The driving force for transferring the heat in the LMTD. (Log mean temperature difference). Heat transfer in a feed heater can fall off owing to fouling of tube surfaces or owing to the presence of incondensable gases. If the heat transfer should worsen the TTD and LMTD would increase. As the condensing temperature is the controlling factor in a heater and this is determined by the bled steam pressure, the feed outlet temperature would suffer from increased T.T.D. The operation engineer must be aware of the above mentioned facts and should always try to optimise the heater performance. The following steps describe the operation procedure involved with HP and LP heaters.

1.8

L.P. Heaters Before putting the feed heaters into operation ensure that:

1.8.1

All maintenance works on valves and equipment of regenerative system have been completed.

1.8.2

All pressure gauges, temp. gauges level instruments and gauge glasses of LP heaters and gland cooler No.2 have been taken into service.

1.8.3

Deaerator is ready for operation.

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1.8.4

Extraction line drain valves are open.

1.8.5

Heater vapour lines are cascaded and connected with condenser.

1.8.6

Condensate system is running normal up to LP heater inlet an recirculation.

1.8.7

Sufficient make up water supply is available.

1.8.8

Main condensate line drains are closed.

1.8.9

Drip pumps are ready for operation.

1.8.10

Gauge glasses are having proper lightning.

1.8.11

Drip control valves are working normally from remote.

1.9

Charging From Water Side

1.9.1

Open the heater vent.

1.9.2

Crack open the condensate line inlet valve to the heater.

1.9.3

Observe air being expelled from air vent.

1.9.4

Keep check on heater gauge glass. (In case of tube leakage the heater gauge glass level will start rising)

1.9.5

After complete air has been expelled from tubes (ensured by steady water stream from air vent) open the inlet and outlet valves fully.

1.9.6

Shut the by valve the heater.

1.9.7

The LP heaters are normally charged from steam side immediately after synchronising the set.

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1.9.8

Charging from steam side

1.9.9

Ensure that heaters are properly charged from water side.

1.9.10

Check that extraction line FCN RVs are open.

1.9.11

Open the extraction steam valve slightly and start warming up the heaters.

1.9.12

Ensure that drip system has been properly lined up and ready for service.

1.9.13

Check the temp. rise in heaters and gauge glass levels.

1.9.14

Gradually open the extraction steam valves fully from LP heater 2 to LP heater 4.

1.9.15

Depending upon load on the unit divert the drip to condenser or to the drip pumps.

1.9.16

Note down the pressures in heaters and the temperature rise from each heater.

1.9.17

Check that gauge glass level and remote level indication in UCB are matching.

1.10

H.P. Heaters

1.11

Precharging Requirements:

1.11.1

Check that there is no PTW pending on any of the components of HP heaters.

1.11.2

Ensure proper lightning for level gauge glasses.

1.11.3

Ensure that root valves of all level switches and level instruments are open.

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1.11.4

Ensure that pressurised condensate supply is available for group protection valve. (This may vary depending upon the type of group protection device)

1.11.5

Ensure that valves as air lines going to condenser and to Low pressure heater 4, from H.P. heater 5 are closed

1.11.6

Ensure that all the feed line drains concerning HP heaters are closed.

1.11.7

Check that H.P. heaters tube vents are open.

1.11.8

Check that drip valves interlock is working properly.

1.12

Charging of heaters (Water side):

1.12.1

Open the charging valve to such an extent that the heater will get charged slowly and smoothly and the air in the system will be properly released through the tube vents

1.12.2

When the air has been expelled and a steady flow of water stream starts coming out of the tube vents, then close the air vents. Feed water pressure in the heaters will start rising. Wait until feed water pressure in the heater is same as the feed water header pressure.

1.12.3

At this point the group protection valve will open fully. After group protection valve opens fully, the isolating valves at the inlet and outlet of HP heaters can be opened fully.

1.12.4

Check that group protection valve operates properly on H.P. heater drip level high interlock. If operating properly charge the heaters again and close the H.P. heaters by valve in the feed line.

1.13

Charging of heaters (steam side):

1.13.1

Ensure that feed water heaters are properly charged from water side & group protection valve is ready to operate in any emergency.

1.13.2

Ensure that turbine load is proper (load> 40%) and is being increased.

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1.13.3

Line up the drip system and ensure that local and remote gauge glasses are in working order.

1.13.4

Check that feed heater protection and interlocks have been checked and are O.K.

1.13.5

Check that condensate supply to FCNRV's is normal.

1.13.6

Check that the shall drains are closed.

1.13.7

Crack open the extraction line steam valve and start warming up the heaters, keep careful watch as shall pressure, drip level and for any other abnormalities

1.13.8

Cascade the H.P. heater air lines on open the valve connecting to LP heater 4. Close air line valve from HP heater to air lines on open the valve connecting to LP heater 4. Close air line valve from HP heater to condenser.

1.13.9

Close extraction line drain valves.

1.13.10

Gradually open the extraction valves fully. Keep watch on heater level. Match the local gauge glass level with remote indication in UCB & local . Control the drip level with the help of drip valves if required.

1.13.11

Note down extraction pressure, heater shell pressure, rise in F.W. temperature and drip level for each heater when stabilised.

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A.

START UP OF TURBINE SYSTEMS Before starting the actual rolling of the turbine, the following equipments and systems are to be commissioned.

1.

ENSURE C.W. SYSTEM IS RUNNING NORMAL

1.1

Ensure that raw Clarifier Water Pumps, Clarified Pumps and Clarified-booster pumps are in service.

1.2

Inform the operator to check the Basin level and C.T. Pumps and C.T. Fans, if in service, should be running normal.

1.3

Inform C.W. Pump operator to carry out prestart checks on C.W. Pump and ensure whether all permits from Maintenance Division are cleared.

1.4

Inform Elect. Controller to rack in breaker of C.W. pump for availability of power.

1.5

Check the opening of CW discharge valve and check whether it has opened fully from UCB.

1.6

After obtaining clearance from operator inform the operator through the intercom, that CW pump is being started.

1.7

Start the CW pump by closing control switch and observe and note down the amperage of the pump and the amp. should be steady at its rated amp. value.

1.8

Ensure from operator the post start check are complete and healthy for CW pump.

1.8.1

Ensure from maintenance division that all permits as C.W. booster pump are cleared.

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1.9

Inform CW pump operator to give the prestart checks on CW Booster pump.

1.10

Inform Electrical operator to switch on the power and after obtaining clearance from operator, announce through intercom that the particular pump is being started.

1.11

Start the CW Booster pump by closing the control switch and the amperage should be steady and not more than rated value.

1.12

After 5 minutes run of the booster pump, the pump is to be stopped and to be started again when turbine speed comes to 1100 rpm.

2.

ENSURE CONDENS ATE SYSTEM IS RUNNING NORMAL

2.1

Inform Turbine charge hand to start the D.M. make up pumps, if already not running after checking D.M. tank level and line up of connected lines.

2.2

Inform Condensate pump operator to open for hotwell make up and maintain hotwell more than 3/4th of the gauge glass.

2.3

Check the protection and interlock of condensate pump and inform condensate pump operator to carry out prestart checks on the Condensate Pump.

2.4

Inform turbine operator to line up condensate system.

2.5

Inform Elect. operator to restore power to that condensate pump and after obtaining clearance from condensate pump operator, announce through intercom that the pump is being started and the amperage should be within rated amp and not hunting .

2.6

If hunting, ask the condensate pump operator to check the pump vapour line valve to be opened properly and also to check the pump suction strainer and otherwise trip the pump and start the other standby pump putting impression switch to 'ON' position.

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2.7

Ask the chemist to check the quality of condensate to ensure that there is no condenser tube leakage and take water to Deaerator after charging L.P. heater from water side.

2.8

Keep the pump in service on recirculation.

3.

ENSURE FEED SYSTEM IS RUNNING NORMAL

3.1

Maintain D/A level normal by running condensate pump system normal and maintain pressure and temp, in Deaerator at rated value by Auxiliary steam.

3.2

Ensure that all permits are cleared from Maint. Divisions for BF pump and HP heaters.

3.3

Inform BFP pump operator to line up the pump after ensuring the protection & interlock are healthy.

3.4

Inform Turbine operator to line up HP heater after checking the interlock and inform Elect. operator to restore power to the pump.

3.5

After getting clearance from BFP pump operator to start & announce that the pump is being started.

3.6

Start the feed pump and keep the pump on recirculation by opening the recirculation valve.

3.7

Watch and note down the amperage of pump and after about 15 minutes when the brg. temp. gets stablished, and charging the feed line up to F.R. station, open the discharge valve.

3.8

Inform turbine operator to charge HP on water side.

3.9

Check the other two BF pumps for their availability and keep the other BFP available on interlock by putting the interlock switch on 'P'.

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4.

ENSURE GENERATOR SEAL OIL & HYDROGEN COOLING SYSTEM ARE NORMAL

4.1

Ensure the Main oil tank level is normal and quality of oil to be O.K.

4.2

A.C. seal oil pump should be running and Check the availability of D.C. seal oil pump.

4.3

Hydrogen pressure in Generator casing should be maintained at rated value and seal oil system and H2 cooling system running normal.

4.4

A.C. standby oil pump should be running. Lub. oil pressure at rated value at bearing header and also check the availability of D.C. oil pump.

4.5

Lube oil pump interlock switch should be 'ON' and oil temperature at bearing seal should be around 40°C.

4.6

Check protection and interlock of lub. oil system.

5.

ENSURE TURBINE ROT OR IS ON BARRING GEAR

5.1

Check the protection of Barring gear (barring gear should not start when lub. oil pressure rails below 0.3 Kg/cm2).

5.2

Ensure that turbine rotor is at stand still position and lub oil system running start the Barring gear motor.

5.3

Note down the amp. of the motor and check Barring gear protection and again restart Barring gear.

5.4

Keep a constant watch on lub. oil pressure and temp.

6.

ENSURE AUXILIARY STEAM LINE IS CHARGED

6.1

Inform boiler operator to charge the aux. steam line from running unit or from M.S. line of its own unit. (Inform the adjacent units of this activity).

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6.2

Keep the drain valve near the Gland steam Cooler open and charge the steam line for ejector, gland steam cooler and steam seals by opening the valve.

6.3

After the line is heated up (for 15 minutes to 20 minutes) throttle the drain valve near Gland Steam cooler to avoid wastage of steam.

7.

VACUUM PULLING

7.1

Ensure CW pumps are in service

7.2

Ensure condensate system in service, Main ejectors, (both) L.P. heaters (all) are charged from water side, all valves subjected to vacuum should be sealed by condensate water.

7.3

Ensure that turbine is on Barring gear.

7.4

Ensure that Auxiliary steam is charged from 16 at header to turbine seal and ejector header.

7.5

Close the vacuum breaker valves near main ejector and fill the funnel with DM water for sealing.

7.6

Prior to charging the starting ejector. Open the drain valve at the isolating valve of steam line.

7.7

Start GSC ejector and it steam to seals.

7.8

Open the drain valves the condenser from the first stage of the ejector.

7.9

Open the steam to ejector, through isolating valves when vacuum in condenser is 400 mm of Hg. and see the steam pressure to main ejector of rated value and see that vacuum is steadily rising in the condenser and stop the starting ejector by closing the air and steam valve.

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B.

STARTING OF TURBINE FROM COLD STATE

1.

PRESTART OPERATION

1.1

Check that all prestart requirements are over.

1.2

Before HP/LP by stations are brought into operation check:

1.2.1

ESV, IV are closed.

1.2.2

Oil system of the by station is put into operation by switching on its motor.

1.2.3

Vacuum in the condenser is at rated roughly 600 mm of Hg.

1.2.4

Condensate flow to steam throw off devices in the condenser are established by opening of the valves.

1.3

Ensure that the valves of the by system are fully closed by reading the respective position indicators.

1.4

Set the temperature set point of HP by station at rated value with the help of push button.

1.5

Put the pressure controllers and slave positions of each HP by valves on manual mode with the help of push button.

1.6

Put the LP by valves ‘Auto’ mode and set the temperature set point of LP by station at rated value roughly 200°C with the help of push button by reading its value on the indicator.

1.7

Put the control of LP by valves on 'auto' mode with pressure loop in circuit with the help of selector switch by making the in 'R position and set the pressure set point of rated value roughly as 6.0 at with the help of push button.

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1.8

Check that the HPT evacuating valves and by valves across NRV cold reheat line are tightly closed.

1.9

After the internal superheater flow has been established through start up vent, open the drain valves before by and after by drain valves, open the drain valves of MS, CR & HR lines and also open after LP by drain valves.

1.10

Open fully the HP by with the help of push button and then open the boiler outlet valves and check the temperature control loop is functioning normal.

1.11

Watch the rise of metal temperature of MS, CR & HR lines and after 50°C superheat is available at the superheater outlet open the by valves of MSV for heating the pipe lines upto turbine.

1.12

Open the ESV to CVS drain valves and Open ESV by about 10-20 mm as per the scale according to instruction and heat the steam ission pipe upto control valves to a temp. of 150°C as rated and rise of metal temp. should not be more than 4°C per minute.

1.13

Open the by valves across the NRVs in the cold reheat line and the Drain valves of HPT and heat the HP turbine upto 150°C.

1.14

Check the steam pressure in hot reheat line to be less than 1 Kg/cm2 (gauge) before starting the heating of steam ission pipe upto control valves of IPT and if the pressure exceeds limiting value adjust the set value at 1 Kg/cm2 (gauge) with the help of push button and indicator of LP by station.

1.15

Open the IV to CVs drain valves and open the interceptor valve servomotor by about 10-15 mm as per the scale instructions and heat the steam ission pipes upto control valves to a specified temp, roughly 100°C.

1.16

Close by valve of MSV in the cold reheat lines when steam parameter before MSV are 20-25 Kg/cm2 and 280-300°C & steam ission pipe of HPT and IPT are heated upto 150°C & 100°C respectively.

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1.17

Close ESV & IV and bring the control of LP by valves on ‘Manual' mode with the help of push button.

1.18

Manually close the HP by valves with the help of push button and when the pressure in the reheat line comes to condenser pressure manually close the LP by with the help of push button.

1.19

After having accomplished the heating, check and note down the following readings in the log sheet before rolling the turbine.

1.19.1

Metal temp. of pipes before MSV, and also before ESV, while heating the main steam and reheat steam pipes, the difference in temperature of pipes should not exceed 15°C. But when the turbine is on load, this difference should not be more than 10°C.

1.19.2

Metal temp. of steam ission lines.

1.19.3

Metal temp. of hot reheat line.

1.19.4

Metal temp. of interceptor valve.

1.19.5

Metal temp. of HPT and IPT top/bottom.

1.19.6

Steam parameter before MSV.

1.19.7

Differential expansion of HP rotor, IP rotor and LP rotor.

1.19.8

Axial, shift, total expansion of HPT/IPT and condenser vacuum.

1.19.9

Eccentricity of turbine rotor on barring gear.

1.20

Open the drain valves of 'HPT, IPT, HP and LP extraction valves and open ESV, IV, control valves of HPT and IPT. completely with the help of control gear.

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2.

RULLING INSTRUCTIONS

2.1

Slowly open the by valves of main steam valve before ESV.

2.2

Allow the steam to roll the turbine and check during the process of raising the speed bearing vibration should not exceed 40 microns.

2.3

Check that barring gear has got disengaged and its motor gets switched off automatically.

2.4

At a speed of 500 rpm, stop the steam supply to the turbine by closing the by valves of MSV and listen carefully for any rubbing sound. If any abnormality is found stop the rolling of the turbine.

2.5

If the turbine is in healthy state, again raise the speed to 500 rpm by opening the by valves of MS valve and soak the set for 5-10 mts.

2.6

It is prohibited to raise the speed of turbine if the differential expansion of the turbine rotor reaches to the maximum permissible values.

2.7

At a speed of 1200 rom soak the set for about 20 mts. note that the control valves of HPT tend to close with the rise of speed.

2.9

At a speed of 3000 rpm. hold the turbine at 3000 rpm for about 20- 25 mts, carry out inspection and soaking of the turbine, perform the checking of protection and governing system and tightness test of ESV and control valves of HPT. (Refer fig. 6).

2.9

Raise the speed of turbine to 3000 rpm from 1200 rpm in 5 mts. without any pause. The critical speed of the m/c should be ed as fast as possible to avoid the appearance of rotor vibration.

2.10

Observe the temperature of lub oil entering the bearings and maintain the lub. oil temp. at 40°C by controlling the cooling water supply to the oil coolers, stop the starting oil pump and keep it ready.

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NOTE:

A.

At the speed of 500, 1200 and 3000 rpm note down the following readings in the log book:

B.

i)

Condenser vacuum.

ii )

Axial shift.

iii)

Differential expansion of HPT, IPT and LPT.

iv)

Overall total expansion of HPT, IPT.

v)

Bearing vibration.

vi)

Turbine LPT exhaust hood temp.

vii)

Steam parameter at MSV.

viii)

M.O.P. discharge pressure.

Watch that different metal temperatures have tendency to rise and note down the temperature.

3.

LOADING OF THE TURBINE

3.1

Synchronize the machine with the grid and take a load of 10 to 15 MW, constantly watch the Differential expansion Axial Shift, metal temp., difference between outer and inner surface of the wall of HPT casing and IPT.

3.2

Hold the Turbine at this load for 30 mts. to carry out soaking and listen for rubbing.

3.3

After soaking, close all the drain valves. On steam lines steam ission pipes, HP. IP drain collectors.

3.4

Charge LP heaters from water side and steam side.

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3.5

At the load of 30 MW, close the drain valves in LP heater extraction lines, note the thermal expansion of the turbine and all the other readings, charge deaerator by opening the extraction steam valve close if pressure in 2

deaerator is less than 2 Kg/cm . 3.6

At the load of 60 to 70 MW, put the H.P. heaters in service, charge the HP heaters from water side and steam side, close the H.P. extraction drain valves.

3.7

Put the drip pump in service stop the flange and stud heating.

3.8

At about 80 MW load, start the second condensate Dumo 4 BFP and keep the third as standby.

3.9

At about 150 MW load, change over steam supply to deaerator from extraction opening.

3.10

At the load of 210 MW set the point of H.P. by valves pressure control loop at 140 ata with the help of push button and change over the manual mode of pressure control loops of HP by valves to 'Auto' with the help of push buttons.

3.11

Set the L.P. by valve pressure set point to 6.0 Kg/cm2 (ata) and temp. set point to 200°C. Change over the L.P. by operation from manual mode to 'Auto' mode with pressure control loop in circuit.

4.

CHAMBER HEATING (ROTOR HEATING)

4.1

Purpose Chamber heating is to be carried out whenever the differential expansion of HP & IP cylinders are too much on the negative side that means beyond HP (-) 0.5 and IP(-) 1.5 mm. (for the turbine of 210 MW installed at BTPS supplied by BHEL). Chamber heating is also to be carried out whenever the differential temperature between turbine top and bottom exceeds 50°C.

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4.2

Process Chamber heating is required generally during hot start up of turbine. Chamber heating essentially consists of supplying live steam to the HP rotor and IP rotor through the gland seals at a low pressure. This will help in heating the HP rotor and IP rotor thus help in reducing differential expansion.

4.3

Steps to be taken for chamber heating

4.3.1

Chamber heating should be started only when HP differential expansion is more than -0.5 mm and IP differential expansion exceeds -1.5 mm.

4.3.2

Temperature of live steam should be raised as high as possible and should be higher than the hottest metal temp. of the turbine.

4.3.3

The pressure of steam for chamber heating should not exceed 4 Kg/cm2.

4.3.4

Chamber heating is to be started while the machi ne is on barring gear. During the process of chamber heating if the barring gear stops chamber heating must be stooped immediately.

4.3.5

During the chamber heating process, shaft eccentricity should be watched carefully, which has a tendency to rise. The process is to be controlled in order to maintain the eccentricity within 0.07 mm.

4.3.6

The following parameters to be noted during the process: a) Live steam temperature. b) Differential expansion of HP, IP & LP cylinders.

5.

TURBINE FLANGES AN D STUDS HEATING SCHEMES OF H.P. AND I.P. CASING:

5.1

The 210 MW turbine has been provided with a device for heating flanges and studs of HP and IP casing. The purpose is to lower the temperature difference of the metal, at the width of the casing flanges and between different points over the casing section, also between the casing flanges and studs at their

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corresponding points. By doing so the turbine may be rolled quickly from cold or warm state. 5.2

Live steam is bled from main steam pipe line before main gate valves of the turbine for heating flanges and studs. The device consists of jackets welded to side wall of casing flanges and special piping complete with fitting and measuring instruments for steam inlet, outlet and drains. Special recesses are provided in the horizontal flanges of the H.P. & I.P. casing t plane for age of heating steam to the studs. In the lower half flanges, recesses are provided and in the upper half of the casing along the height of studs there are baffles for guiding the steam flow over the studs.

5.3

The special pipe lines each delivering steam to two separate headers have been provided. Two headers are meant to supply steam to flanges and studs separately.

5.4

The header to the flange jackets supplies steam for heating flanges. And the header to the recess in horizontal t of HP & IP casing bottom flanges supplies steam for heating of studs through holes in the bottom flanges on the right and left side.

5.5

Steam from jackets and recesses in the HP & IP casing flanges is collected in common header and then flows through piping to the condenser steam space.

5.6

The use of device for heating flanges and studs of the casing is permitted only if a careful check is kept over the temperature difference across the metal at the available references points. The measuring and recording of temperature differences should be

carried out during turbine starting at

least once every 10 minutes. 5.7

The temperature difference across the width of the casing flange should be within 50°C. The temperature of outside flange surface should never exceed that measured with a thermocouple at a maximum depth inside the flange. The difference between the flange and stud temperature should not exceed 20°C and stud temperature should never be more than that of the flange.

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5.8

When starting the turbine from cold or warm (temp. of metal of the upper half of the H.P. casing being upto 250°C), heating of flange and studs is permitted provided differential expansion of the rotor is positive and not less than 1 mm. It is not permitted to operate the flange heating device.

i)

If the relative expansion of rotor compared to casing is less than 1 mm.

ii)

If the differential expansion indicating and recording instruments are either out of order or disconnected.

5.9

In order to maintain proper tightening of flange ts, it is necessary to first supply steam for heating flanges and only then after some time to studs. NOTE Due to special constructional features of KWU turbines both the chamber heating and flange and stud heating system is not provided.

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C.

WARM AND HOT START Depending upon the metal temperature of H.P.T. casing in the zone of regulating stage, the type of start can be chosen.

1. 1.1

1)

Metal temperature above 350°C - HOT START

2)

Metal Temp. between 150°C to 350°C - WARM START

3)

Metal temp. less than 150°C - COLD START

PRELIMINARIES FOR WARM OR HOT START Before warm/hot restart, the auxiliary equipment should be started in the same manner and order as in the case of cold start. Before hot or warm start, the starting oil pump should have been working and supplying oil to bearings, the turbine shaft is rolling on barring gear, and one of the condensate pump is operative. Check oil pressure in lubrication and governing system and see draining of oil from bearings. Check that all the control and measuring instruments have been switched on and are working alright.

1.2

If condenser vacuum had been killed, start vacuum pulling after supplying steam to the turbine glands.

1.3

Before starting the heating of steam lines, the vacuum in the condenser should be 600mm of Hg. MSV, ESV, ISV, CVS, of HPT and IPT should be tightly closed.

1.4

Heating of main steam lines, body of ESV, reheat pipe lines, body of IV may be done in case the temperature of these elements is 80-100°C less than the temperature of the lower half of the H.P.T casing in the zone of regulating stage and in the zone of steam ission in case of I.P.T. respectively by opening the drains of relevant portion.

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2.

HEATING AND ROLLING OF TURBINE DURING WARM START Read the actual metal temperature of H.P. casing at the regulating stage and should be within 150°C to 350°C. By using the temperature matching chart, determine the desired steam temperature and pressure for rolling the turbine. However, the steam temperature must be more (at least 25°C) than the hottest metal temperature of E.S.V. and steam ission pipes of H.P.T.

2.1

Select the operational mode of H.P. by- valve on 'Manual' and L.P. by on 'Auto' and select for pressure mode of operation, set the set point of L.P. by- station at 6 ata by push button.

2.2

Set the temperature control loop of H.P. by- station on 'Auto' and set the temp. set point as per the requirement on the down stream side of H.P. by station, temperature control loop of L.P. by- stations should be on 'Auto' and temperature should be set at 200°C and ensure that the evacuating valves and by- valves of NRVS in the cold reheat lines are closed.

2.3

Open H.P. by- valve and raise the steam parameters of boiler to desired value, heat the main steam cold reheat lines and open the by- valves of MSV and ESV by about 15-20 mm and heat the steam ission pipes upto control valves.

2.4

Check that the steam pressure in hot reheat line should not exceed 1 Kg/cm2. If required, manually close a little the HP by- valve, open the IV servo motor by 10-15 mm as per scale and heat the steam ission pipes upto control valves of I.P.T. control valves of I.P.T. should remain tightly closed during this process and during the process of heating of the steam pipe lines check the draining system is alright.

2.5

Having accomplished the heating, check and note down the various metal temperatures viz. of steam pipes, ESV, IV, IP casing and HPC at the regulating stage, ensure that the desired matching steam temperature is available at ESV.

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2.6

Manually close the HP by- valves with the help of push button.

2.7

Bring the control of L.P by- valves op 'Manual mode' with the help of push button, open the L.P. by- valves, with the help of push button when the pressure in the reheat line comes to condenser vacuum close the LP by valves.

2.8

Check that the eccentricity and differential expansion of the rotor are within limit.

2.9

With the help of the speeder gear fully open IV, ESV, CVS of IPT and HPT. And slowly open the by valves of MSV and roll the turbine as per guide lines given, to the synchronising speed.

2.10

Checking should be made during rolling as in the case of cold start-up.

2.11

Synchronise the set and load the set to 20-30 MW. All the drains must be closed after some load has been taken on the turbine, the raising of steam parameters and loading of the set is to be carried out as per the curve and guide lines of loading for the warm start.

2.12

After loading the unit, set HP and LP by- stations as follows:

2.12.1

HP by- station pressure control loop: 14 ata, automode.

2.12.2

Temperature control loop : 380°C, automode.

2.12.3

LP by- stations Operational mode-pressure control. Pressure control loop: Auto with set point at 6 Kg/cm2 (abs) Temp. control loop: 200°C, automode (based on BTPS parameter).

3.

HOT ROLLING OF TURBINE Read the actual metal temperature of the following elements:

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74

a)

Metal temp. of body of ESV.

b)

Steam ission pipes of HPT and IPT.

c)

HPT in the zone of regulating stage.

d)

Steam ission chamber at IPT.

e)

Body of IV.

Now with the help of steam matching chart, determine the desired steam temperature and pressure for rolling the turbine. Steam temperature before ESV at the time of roll must be more (at least by 25°C) than the hottest metal temperature of elements mentioned above. 3.1

Ensure that all the prestart conditions such as oil system in operation, vacuum in the condenser is more than 540 mm of Hg. flow of condensate in steam thro device is O.K.

3.2

Set the H.P. by valves on 'AUTO' mode and set the pressure setting at 5-8% higher than the actual pressure available in the main steam lines.

3.3

Set the L.P. by stations also on 'AUTO' with pressure control mode with set point at 6 Kg/cm2. Put the temperature control loops of H.P. by valves on 'AUTO' mode and set the temperature set point at 50°C higher than the cold reheat pipe metal temperature, change the temperature set point upward to meet the boiler requirements. Heating rate of cold reheat pipe lines and reheater should be within limit and set point should not exceed 380°C.

3.4

Check that the by valves across NRV's in cold reheat lines are closed. Open the evacuating valves to release the entrapped steam from H.P. casing.

3.5

Raise the steam parameters of Boiler. HP-LP by stations shall cut in automatically under pressure impulses provided other logic conditions are being met, the H.P. valves shall keep on opening and allow the entire steam generated by the boiler until the flow ing capacity of the HP by valves corresponding to set pressure is fully utilised.

3.6

As the difference of pressure between the actual value and set point exceeds the allowed limit, an alarm shall appear. At this stage, slide upwards the

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pressure set point, but the set point valve should be 2-3% lower than the value indicated in the instrument, after attaining the desired steam temperature and pressure, suitable for rolling of the turbine, hold the firing rate of boiler. 3.7

Heat the transfer pipes between IV and CV of IPT by opening IV by 5-10 mm as per scale, the valves in the drains of these pipes should be kept full open, prior to the opening of IV, after heating these pipes corresponding to the available steam temperature. Close IV fully.

3.8

Open fully MSV's and IV with the help of the control gear.

3.9

Turbine will start rolling through IPT. As soon as the speed of the rotor rises above 3.4 rpm, check that barring gear gets disengaged and its motor cuts out automatically. Check that the valves in the evacuating lines of HPT casing are closed.

3.10

Start opening of CV's of IPT and raise the turbine speed to 3000 rpm without pause, at 2800 rpm check that main oil pump takes over. Stop the starting oil pump.

3.11

Synchronise the set and take around 20 MW load on the unit. Close all drains.

3.12

Immediately load the turbine at the rate of 5 MW per minute. As soon as the steam starts flowing through H.P. turbine, ensure that the H.P. by valves starts closing, loading the set further as per the curve for hot start of turbine. (Refer fig 7).

3.13

After loading the unit, set the H.P., L.P. by station similar to that in case of warm start (Described earlier).

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FIG.7

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77

D.

TURBINE SHUTTING DOWN FROM FULL LOAD.

1.

PLANNED SHUT DOWN

1.1

Inform the boiler house that the turbine would soon be shut down.

1.2

Check the starting oil pump and also availability of A.C. & D.C. lub. oil pumps.

1.3

Reduce the load at a rate of 3 MW per minute at rated parameters by operating control gear motor.

1.4

Watch the axial shift & differential expansion of ;he rotor and cylinder, after reducing the load to 160 MW switch off the H.P. Heater on steam side and drain heating steam condensate by opening the drain valves.

1.5

At load 90-100 MW switch off one of the condensate pumps and feed pumps and at 70 MW load check the drip pump gets switched off under automatic controller action and also ensure that auxiliary power supply is changed from unit to reserve.

1.6

Maintain Deaerator & condenser hotwell level normal

1.7

At load 10 to 12 MW open by valve of MS before ESV and close valve on Main Steam line.

1.8

Reduce the load to about 5 MW slowly. Trip the unit through any protection, check the ESV, IV and control valves get closed.

1.9

Isolate lub oil cooler from cooling waterside one by one to maintain lub oil temp.

1.10

Ensure that generator is isolated through low forward power relay and the time for stopping the steam supply to turbine and isolation of generator should not be more than 4 minutes.

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1.11

After closure of the Control valves immediately close the main steam valves near Boiler outlet and check that by of main steam valves are also closed.

1.12

Stop the other BF pump depending upon the level of the Boiler drum.

1.13

At 2800 rpm, start AC lub oil pump and AC seal oil pump, check the Lub oil press and A.C. seal oil press is normal.

1.14

When the rotor comes to a stop, start the barring gear and roll the rotor continuously on BG till temp. of lower part of HP casing at regulating stage drops to 170°C, engage the barring gear lever at stand still condition of rotor and then start the barring gear motor and make sure that rotor rpm is 3.4. when put on Barring Gear.

1.15

Break the vacuum by opening Vac. Breaking valve and cut off the steam supply to main ejector, gland steam cooler and steam to seals by closing the respective valves.

1.16

When maximum turbine metal temp. comes down below 200°C. Open cylinder, transfer line and main steam line drains.

1.17

Barring gear and lub. oil pumps can be stopped if necessary.

1.18

Condensate and C.W. pumps can be stopped when LP exhaust temp. comes below 40°C.

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E.

IMPORTANT INSTRUCTIONS DURING TURBINE RUNNING

1

ROUTINE CHECKS

1.1

The turbine is capable of accepting the variations from the rated conditions within the limits stated below :

1.2

Live steam pressure

: 117-143 Kg/cm2

Live steam temperature

: 527-543°C

Reheat steam temperature

: 527-543°C

Sharp fluctuation of temperature and/or load on turbine should be avoided as far as possible. Sharp fluctuations consume the fatigue life of vital components.

1.3

Turbine operation with the steam exhaust to atmosphere is forbidden. In case of rapid drop in vacuum and opening of atmospheric valves, the turbine should be stopped immediately. The turbine may be restarted only if the exhaust part of the turbine and the condenser have cooled down to 55°C.

1.4

The main steam and reheat steam temperature should preferably be equal to or more than the metal temperature of steam ission elements.

1.5

When the turbine has tripped due to action of protection or by turbine shut down switch, check the operation of the equipments mentioned below along with the closure of emergency stop valves.

1.5.1

Main steam stop valves must be closed.

1.5.2

NRV's on extraction lines must get closed.

1.5.3

Generator circuit breaker should be open.

1.6

If there are more than one indicators for the same measurement, then the one which is giving favourable reading should not be assumed to be correct one.

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1.7

If any of the control valves gets closed accidentally the load on the turbine would get reduced. Trace out the valve by comparing the pressure reading after all control valves.

1.8

The turbine must be stopped manually independent of the action of relevant protection under following situations: a)

Sudden appearance of excessive vibrations.

b)

Water hammering

c)

Oil ignition

d)

Emergency governor out of order

e)

Oil temp. rito 75°C at the drain from the bearings.

f)

Drop of oil level in the tank below the lowest permissible value.

g)

Appearance of metallic noise in the turbine steam flow path.

h)

Axial shift of the rotor at the thrust bearings reaching limiting value.

i)

Accidental vacuum drop to 540 mm.

j)

Increase of live or reheat steam temperature upto 565°C.

k)

Lubrication oil pressure has dropped to 0.5 Kg/cm 2 gauge and lubrication pump (emergency) has failed to start.

i)

Sharp fall in the main steam temperature from nominal value to 450°C.

1.9

m)

Increase in speed beyond 3360 r.p.m.

n)

ESV, IV or control valves have seized.

In order to remove salts deposited on the guide and moving blades, the flushing of turbine flow path should be carried out with saturated steam during next cold start up.

1.10

Analyse each drum of oil before filling in the oil tank, in case the filling is done from oil drums.

1.11

The generator should operate at a network frequency of 50 s., which, correspond to generator rotor speed of 3,000 r.p.m. The net work frequency below 49.0 or over 50.5 s. is not allowed and immediate measure should be taken for restoring it within 49.0 to 50.5 s.

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1.12

Turbine operation on load limiter is not recommended for a longtime except in emergency. Such operation hampers control of network frequency.

1.13

General temperature rise in oil supplied to the bearings at constant pressure and constant cooling water temperature indicates the choking of oil coolers.

1.14

Dust off the turbine at least once a shift, special care should be taken while cleaning the levers and links of governing and steam distribution systems.

2. 2.1

IMPORTANT DO’S DURING TURBINE RUNNING Do every Shift. 1)

Close ESV & IV 15 mm by hand wheel by one and reopen back to full.

2)

Check

by

draining

oil

from

bottom

of

MOT for

checking

water/sediment in the oil. 3)

Position of emergency governor knob selector (both emergency governor should be in service).

4)

Check all vapour exhaust fans are in service.

5)

Check Main Oil Tank level (280 mm) is normal.

6)

Dust off the turbine.

7)

Check the availability of H2 & C02 bottles.

8)

Check the quality (moisture, acidity, chemical impurities) in Turbine MOT (Main oil tank) once in a day.

9)

Check the availability of Diesel Generating set.

10)

Check the availability of AC & DC lub oil pumps.

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2.2

Do every week 1)

Take out oil tank filters one by one for routine check up and clean by blowing dry compressed air through them.

2)

Operate the standby equipments in rotation and no equipment should be kept idle for more than one week.

2.3

Do every month 1)

Check the Operation of servomotors for forced closing non-return valves by operating solenoid valves at reduced loads.

2)

Check one by one the full closing of ESV and IV servomotor at reduced load (120 MW).

3.

IMPORTANT DONT'S FOR TURBINE OPERATION

3.1

Don't start the turbine if the control signalling and protection system are not in working order.

3.2

During M/C on Barring Gear if rotor eccentricity exceeds 0.07 mm do not roll the turbine.

3.3

Do not start the turbine with oil temperature at bearing inlet less than 40°C.

3.4

Do not run the turbine on load with control valves servomotor in full open condition.

3.5

During shut down do not open the drains on steam ission pipes and cylinders, till the metal temperature falls below 200°C.

3.6

Do not allow the turbine to run in the steamless condition for more than 4 minutes.

3.7

Do not drain the oil, saturated with hydrogen into Main Oil Tank.

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3.8

Do not allow hot rotor to stand without rolling (Barring gear).

3.9

Do not allow to rotate the rotor by hand if there is not at all oil supply to bearings.

3.10

Do not try to engage barring gear unless turbine rotor is completely stopped.

3.11

Do not supply the steam to turbine and sealings if M/C is not on barring gear.

3.12

Do not overlook abnormality in any important reading.

3.13

Do not hold the set in the critical speed zone while raising the speed of the turbine.

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F.

EMERGENCIES IN TURBINE AND AUXILIARIES

1.

SUDDEN LOAD THROW OFF

1.1

In case of partial load throw off (due to high frequency).

1.1.1

The steam pressure at ESV will increase

FSSS operator will control the boiler pressure.

1.1.2

The turbine load will decrease.

Governor will control the load. If it fails, then throttle the control valves suitably and maintain pressure to normal till the frequency comes down.

1.1.3

Disturbance in differential expan sion

There should be a constant watch on the

vibration, axial shift, eccentricity

supervisory instruments.

1.1.4

Disturbance in condenser level

Adjust and maintain the hotwell level.

1.1.5

Disturbance in vacuum

Check

and

adjust

ejector

steam

pressure and gland steam pressure to normal. 1.1.6

Turbine lub. oil temp will change.

Check and adjust the coolers water flow as necessary.

1.1.7

Disturbance in Deaerator pressure

Deaerator

pressure

tends

to

fall,

maintain it through extraction on 16 ata. 1.2

Partial load thow off due to aux. failure. There is a provision for partial load throw

In

off by help of a relay with a time delay of

equipments operation of partial load

which reduces turbine to 100 MW in

relay will reduce the boiler output

case

suitably in a sequential manner through

of

the

equipments.

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tripping

of

following

case

of the

tripping

of

these

FSSS Scheme.

85

1.2.1

One C.W. pp in case both are running

If the partial load relay fails/not in circuit reduce the turbine load and inform the boiler operator to control steam parameter in case one CW PP or one condensate pp trip. Careful watch may be kept on vacuum. Inform the local operator to check the cause of tripping. Maintain the Deareater and hotwell level.

1.2.2

One BFP in case two are running and standby/does not come on auto remote/ not available.

1.2.3

One condensate Pump in case two are running and standby does not come on auto/remote not available.

1.2.4

And also due to tripping of any one of I.D. Fan, F.D. Fan, P.A. Fan.

1.3

In case of Full load Throw off

Unit trip on protector if it is kept on 'P'.

(due to opening of generator breaker ) 1.3.1

The turbine may trip gear due to over-

Close the control gear handwheel.

speeding (if the speed can be controlled by closing control valve, close the

Check that ESV and Control valves are

control valve immediately otherwise trip

closed.

the turbine by emergency trip button). Close the valves in the M.S. Line. Close the Extr. steam valves. (Refer turbine shutdown procedures).

2.

SUDDEN INCREASE OF LOAD FROM FULL LOAD

2.1

Low frequency

Since the turbine is on governor control the load will increase due to fall in

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speed. Reduce the load by the control gear and bring the boiler parameter and load to normal. 2.2

Due to sudden rise of boiler drum

Bring back the load/governing wheel

pressure.

pressure to normal by control gear and inform the boiler.

3.

VIBRATION HIGH Normally the vibration bearings should

Check the turbine cylinder drain should

be within 40 microns. If it exceeds the

not be cold (if necessary open the drain

limit, causes should be shut down.

valve for few minutes if turbine is on load. Check brg. Oil press. Flow and temp. to be normal. Check for any rubbing sound etc. Reduce the load/speed.

4.

TURBINE BEARING OIL PRESS. LOW Check the main line pressure and maintain it.

5.

BEARING OIL INLET TEMP. HIGH

5.1

Check the cooling water valves are open in Oil coolers and vent the coolers. Put the standby cooler in service, ensure CW Pp is running normal. Check bearing oil outlet temp. (less than 65°C).

6.

DIFFERENTIAL EXPANSION HI/LOW

6.1

Normally the rotor gets long during

Check

running and gets short during shutdown.

load/speed. Check the valve for flange

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the

steam

temp.

Reduce

87

The expansion is to be controlled by

heating are in open condition if rotor is

itting steam or shutting off supply to

long or close if rotor is short. Check and

flange and stud heating/chamber heating

adjust gland steam temp.

accordingly. In case if it goes beyond control, the m/c to be tripped.

7.

AXIAL SHIFT HIGH

7.1

In case of excessive shift the turbine will

Check the vacuum to be normal.

trip through the protection. 7.2

Sudden change in load

Control the load and maintain the steam parameter.

7.3

Abrupt change of steam parameter

Control the load and maintain the steam parameter.

7.4

Sudden closure of FCNRV of heater

Control the load and maintain the

(HP/LP)

governing

pressure,

if

heaters

are

healthy open FCNRV. 7.5

Variation in Lub. Oil temp. pressure and

Maintain lub. oil pressure temp. pressure

quality.

and temp. for quality get the oil tested from laboratory and if necessary oil is to be changed. Difference of oil temp. from thrust bearing front and rear outlet should not be more than 3°C.

8.

LOSS OF VACUUM If there be any loss of vacuum, start the standby ejector at the earliest. Still if it does not improve, start starting ejector. With no further improvement of vacuum, reduce the load as required to maintain the vacuum at 700 mm. Meanwhile try to detect the specific reason which may be as follows :

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8.1

Steam ejector not properly functioning.

8.2

HIGH LEVEL IN CONDENSER

8.2.1

Malfunctioning of condensate PP valve

Check that steam pressure in 6 Kg/cm2.

or

Check

the

normal

running

of

the

condensate PP start standby. Pump. Check the operation of valve from UCB by taking it to manual, if not alright control the hotwell level by- valve.

8.2.2

Malfunctioning of DM make up valve.

Close valve pressure from UCB and watch that hotwell level falls.

8.2.3

Condenser tube leakage

If the above operation a & b fails to control

the

hotwell

level,

get

the

condensate water tested by laboratory to confirm the leakage. If the tube leakage is very high,

it may not be possible to

pump out the condensate from the condenser when the condensate level will gradually increase. Ultimately if the water level rises up to the air suction space of condenser, water will be sucked into air ejector.

When

suction pipe line of the the

same

will

be

supercooled and ejector will not function. Shutdown the

turbine at the earliest to

get the leakage attended. 8.3

CW pump failure

If one pump is tripped, reduce the load. Meanwhile determine the cause of CW PP failure and rectify the defects. Of course if both the CW pumps fails, there is no way out other than to trip the unit.

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8.4

Air leak into system

Check sealing water pressure to valves under Vacuum is normal. Check starting ejector air valve and vacuum break valve are Tightly closed. Measure the amount of air leakage at air removal

equipment

outlet

and

investigate the source of leak. 8.5

Condenser tube choking

Check the CW inlet and choking outlet temperature. Backwash the condenser or take into service on load cleaning equipment.

9.

LOSS OF BARRING GEAR OR BARRING GEAR FAILS TO START

9.1

For loss of electrical supply D.G. set will

If not possible to start the DG set,

come automatically otherwise start.

attempt to turn the shaft by slings with the help of over head crane by 180° at regular intervals of 15 minutes after cutting in the D.C. emergency lub oil pump.

9.2

Smoke from turbine seals.

Check

differential

expansions

are

normal. Reduce seal steam temperature if high.

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A.

SEAL OIL SYSTEM

1.0

Prestart Checks

1.1

Seal oil system commissioning is required prior to filling of hydrogen in the machine. The following works should be completed before putting up the system into operation.

1.2

The turbine main oil tank should be filled upto the required level with centrifuge oil.

1.3

Following services should be made available i)

Electric power for A.C. seal oil pumps motor.

ii)

D.C. Power for D.C. seal oil pump motor, controls relays, starting and signalling s.

iii)

Cooling water supply for seal oil coolers.

iv)

Dry clean compressed air for filling the generator.

2.

Lining Up The System

2.1

Open the valves for suction and discharge of AC seal oil pump, its coolers and oil filters. Open the values leading the discharge oil to damper tank.

2.2

Close all other valves.

2.3

Charge the seal oil line with oil by gravity for MOT, vent air from cooler filter etc. and close the discharge valves of A.C. seal oil pump.

2.4

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Check the venting of pressure gauges is over.

91

2.5

Start the A.C. seal oil pumps and slowly open the discharge valve.

2.6

Wait till Damper tank is full and the oil level in hydraulic seal rises to a point midway.

2.7

Check the oil level in hydraulic seal oil tank above lower gauge glass but below upper gauge glass.

2.8

Check the alarms for high/low level in hydraulic seal tank and damper tank to be working all right by simulating both the conditions by level switch with help of C&I.

2.9

Charge the cooling water flow to seal oil cooler.

2.10

Check the centrifugal fan in service in the main oil tank.

2.11

Check the suction and discharge pressure of A.C. seal oil pump.

2.12

Check oil pressure before and after the filter.

2.13

Apply thrust oil pressure by regulating inlet and outlet valve of P.O.R. carefully to get the required pressure.

2.14

Open damper tank by- valve

2.14.1

Open inlet and outlet valves of DPR.

2.14.2

Ensure A.P of the seal oil.

2.15

Now there will be flow through the seals. Ensure that the flow on H2 side is normal.

2.16

Wherever the pressure of air or gas inside the generator is less, drain the oil from the hydraulic seal tank.

2.17

Now bring the damper tank in service.

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2.18

Ensure that POR & DPR are working satisfactorily.

2.19

Ensure that there is no leakage of oil into the casing.

2.20

Check seal oil pressure at generator seal.

2.21

Check the flow of oil from return sight glasses at generator seals to be uniform and continuous.

2.22

Seal oil system is now in operation and healthy.

B.

HYDROGEN COOLING SYSTEM

1.

Filling Operation

1.1

Purging of Air in the Generator Cooling by CO2.

1.1.1

In order to avoid the formation of an explosive mixture of hydrogen and air in generator at any time either when the generator is being filled with hydrogen prior to being placed in service or when hydrogen is being reproved from the generator prior to opening the generator for inspection or repair, CO2 is used as the inert purge gas. CO2 is itted from CO 2 manifold to generator casing at bottom by opening the valves of several cylinders at a time. Rate of ission is being controlled normally by regulating the valves on the manifold. The generator should be at stand still or barring gear and shaft sealing system must be in operation.

1.1.2

To avoid excessive frosting, the CO 2 flow rate should be carefully regulated. The sample of gas taken from the generator casing should be periodically analysed by means of portable gas analyser. When CO2 percentage reaches 98%, the filling of CO 2 can be stopped and preparation for filling hydrogen can be made.

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1.2

Hydrogen Filling

1.2.1

After achieving 98% CO2 concentration and a pressure of 0.15 to 0.2 Kg/cm

2

inside the machine, filling of hydrogen in machine can be started. 1.2.2

Before itting H2 into machine following checks should be carried out. i)

Ensure that generator is gas tight.

ii) Ensure that all the air has been purged out by CO2. iii) Ensure all valves of gas system are set at the completion of air purging. iv) Check auto starting of stand by seal oil pump. 1.2.3

Usually H2 manifold is provided with a facility to connect five H2 cylinder at a time and also it is connected to H2 plant. Hydrogen is itted into the generator through hydrogen feed pipe which is connected to perforated pipe header inside the generator extending along the length of the cooling at the top.

1.2.4

During process of filling with H2 the CO 2 air mixture is discharged through CO2 feed pipe from bottom.

1.2.5

During H2 filling, continuously analyse the concentration of H2 in gas mixture inside the machine. Sample can be taken from any of valves provided for CO2 manifold. Filling operation is complete if the H2 concentration attains a value of 98% and H2 pressure attains rated value.

1.3

Purging of H2 by CO2

1.3.1

CO2 itted to the bottom of the casing through the CO 2 feed pipe and hydrogen is discharged to the atmosphere through hydrogen feed pipe line. CO2. should be itted till CO2 concentration is 98%.

1.4

Purging of CO 2 by Air

1.4.1

When CO2 concentration in the CO2 hydrogen mixture reached 98%, air filling may be started to expel the CO2 before the machine is opened for maintenance. For this purpose dry instrument air is used.

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C.

STATOR WATER COOLING SYSTEM

1.

Operation

1.1

Keep the pumps interlocking switch in off position.

1.1.1

Check up 415 V, 3 ø, 50 c/s supply for stator water cooling pumps.

1.2

Ensure that one D.M. make up pumps is running and fill up the expansion tank and D.M. water make up tank (if provided) upto their normal value by opening respective inlet valves.

1.3

Supply clarified water to the water line valve to ejector by opening clarified water line valve to create vacuum and thus maintain vacuum in the expansion tank.

1.4

Open the D.M. water valves before and after the stator water pumps, stator water coolers and mechanical filters.

1.5

Open the stator by valve and start the pump and slowly open the discharge valve to full.

1.6

Adjust the cooling water pressure and flow.

1.7

Charge the other cooler from D.M. water side and bring the temperature of D.M. water to 40°C.

1.8

Charge the cooling water for secondary stator water cooler.

1.9

Charge retifier for Excitor (RCU) by opening D.M. water inlet valve and adjust the flow by the control valve.

1.10

Proper venting of stator winding cooling lines is to be done. Now adjust the pressure and flow of D.M. water entering the hallow stator winding.

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1.11

As soon as D.M. water circulation is achieved through stator winding at normal pressure and flow, interlock switch of stator water cooling pump should be placed on auto position.

1.12

During normal operation constant watch to is to be kept on parameter such as pressure, temperature, specific resistivity, Ph value, DM water level in expansion tank etc.

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A. 1.

PRE-SYNCHRONISING CHECKS & SYNCHRONISING PROCEDURE PRE-SYNCHRONIS ING CHECKS After attaining the speed of 3000 rpm. Generator is to be synchronised to the grid for supplying power. Before starting, following should be checked and ensured:

1.1

Instrument supply to all indicators and recorders is "ON".

1.2

Clearances from C&I and electrical division that all instruments and equipment are available.

1.3

All the flags on relays are reset and annunciation circuit is healthy.

1.4

Supply of oil to generator bearings and shaft seals is available and flow of oil is normal.

1.5

H2 pressure and purity are upto rated value.

1.6

H2 gas coolers water supply should be checker) for desired quality and ensure normal temperature pressure and flow.

1.7

Stator water cooling system is available.

1.8

Protection and metering circuits are healthy.

2.

STEPS FOR GENERATOR SYNCHRONISING:

2.1

Ensure the availability and completeness of all the equipment and circuits. Take clearance from Electrical Division for starting the set.

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2.2

Ensure that the insulation resistance of the system is within permissible limits especially if the generator is being synchronised after a long time or in rainy season. If the insulation resistance of the system is low, dry out of stator winding and associated bus duct should be carried out.

2.5

Check seal oil system for seal oil pressure, flow and temperature. If the oil pressure is not proper, adjust differential pressure regulator. In case of temperature, adjust cooling water flow.

2.4

Check H2 cooling system for H2 pressure, purity and gas leakage. If the H2 pressure and purity are low, fill more H2 cylinders for increasing the pressure and purity.

2.5

Charge stator winding coolers with distillate and ensure quality, pressure, flow and temperature of the distillate.

2.6

Check that generator breaker and Generator field breaker are open. If not, open Generator breaker or field breaker as the case may be.

2.7

Advice rolling of turbine to rated full speed (3000 rpm).

2.8

Check bearing Vibrations and rubbing etc. if any inside the generator during rolling or any abnormal sound. If the vibrations on the generator bearings exceed the permissible limits (60- micron) shut down the machine and check the bearings. In case of rubbing abnormal sound, shut down TG set and check clearance between stator and rotor.

2.9

Check temperature of bearing, seal babbitt and drain oil. If the babbitt temperature of bearing or seal is high, check oil flow and vibration on that bearing. If the temperature goes beyond 80°c shut down the T.G. set and check the bearing.

2.10

Throttle inlet and outlet valve of H2 gas coolers according to gas temperature. Do not allow the gas temperature to rise above 55°C.

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2.11

Ensure that the machine has attained the rated speed of 3000 r.p.m. Obtain a go forward signal from boiler and turbine operator to synchronise the machine.

2.12

Enquire from the switchyard control room about synchronising of machine to the required bus.

2.13

Close the isolator for bus.

2.14

Ask switchyard control room operator to close transformer side isolator and report back to UCB about proper closing of the isolators after physically ing the same. If the isolators are not closed properly, open the isolators. Give shut down for checking alignment, operating mechanism and limit switches. Take corrective measures.

2.15

Check that the synchroscope cut off switch is "OFF" and synchronising check relay "SKE" by switch is on "IN CIRCUIT" position. If not, put these switches in the said positions.

2.16

Close exciter field breaker. Give closing impulse for about 5-sec., and release the switch when Red lamp glows indicating the closing of breaker.

2.17

Voltage will start building up due to residual magnetism. Check that the voltage is equal in all three phases. If voltage on the phases is not equal, check PT fuse and replace the blown one, if any. If the difference is more than 1KV, inform EM Divn., for thorough check up. Open the exciter field breaker and isolators. Check insulation resistance of all the three phases and take necessary action.

2.18

Put Auto/Manual excitation mode selector switch on "Auto" position voltage will start building up. Check that the rate of building up is normal. If the rate of voltage build up is more than the permissible limits, switch over to "Manual" mode and build up voltage manually.

2.19

When the voltage has built up approx., upto 10 KV, check that the voltage and frequency of the incoming machine and that of the system and approximately equal. If the frequency is not approx., equal, give impulse to

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the load changer to bring the frequency approx. equal. If the excitation mode is on "Auto" it will automatically match the voltage; otherwise in "Manual" mode, give impulse to field rheostat switch to match the voltage. 2.20

Switch on the synchroscope. If the frequency of the incoming m/c is higher than the system frequency, the synchroscope pointer will move in the clockwise director, and if the frequency is lower, it will move in anti-clockwise direction. Speed of rotation of the pointer will depend upon the difference in frequencies. Give impulse by load change switch to have very slow clockwise rotation.

2.21

When the voltage and frequency match, the synchroscope will move very slowly in the clockwise direction. This position shows that:

2.22

i)

Phase sequence of generated voltage and system voltage is same.

ii)

Effective values of both the voltage are same.

iii)

Frequency of both the system and the incoming m/c is same.

Give closing impulse to Gen. breaker the instance when the synchroscope pointer is in between 11 and 12 ° Clock position which indicates synchronism by the glowing of lamp at the Gen. annunciation .

2.23

Take 10-20 MW load on the machine. Ask boiler operator to carry out necessary operations on boiler side to raise the steam pressure and temperature, so that load can be raised.

2.24

Put synchroscope switch to "OFF" position. Return synchronising switch to "OFF" position and lock it. Ask turbine operators to carry out necessary operations on turbine side required for raising the load.

2.25

Put "antimotoring" protection switch on "ON" position after taking some load on the machine (say 20 MW).

2.26

Gen. voltage and P.F., will be maintained by AVR if the excitation mode is on "Auto", otherwise, maintain Gen. voltage and PF by varying the field rheostat

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from the Gen. control desk. If excitation mode is on manual, then change over to "Auto" mode after matching the parameters. (Refer fig. 8). 2.27

Slowly raise the load on Generator upto 80 MW (Follow the guide lines given for loading the machine). Now the voltage and power factor will be maintained by the automatic voltage regulator (AVR). However, the level can be changed by varying the rheostat resistance.

2.28

Changeover 6.6 KV auxiliary bus from station supply to unit auxiliary supply taking both the unit auxiliary transformer into circuit. Check that the unit auxiliary supply incoming breakers are racked in service position, springs are charged and "Local/Remote" switches are on "Remote" position.

2.29

Keeping Gen. winding & core temperature, Gen. transformer winding temperature H2 gas temperature generator seals and bearing metal temperature in limits by adjusting cooling water flow to Generator gas coolers and oil coolers. Load the generator upto 150 MW as per guide lines available.

2.30

At this load, check Gen. bearing and seals temp. Gen. Wdg./Core temperature Gen. T/F Wdg. temperature H2 gas temperature performance of automatic voltage regulator and cooling water flow to R.C.U. If Gen. Wdg/Core temperature is higher adjust distillate flow and cooling water flow to gas coolers. If Gen. T/F wdg. temp. is high, check that all the cooling fans and pumps of cooler banks are in service. If the AVR is not functioning properly take the voltage control on "manual" mode.

2.31

Check exciter winding temperature & slip ring sparking. Ensure that the exciter voltage and current are within permissible limits.

2.32

Check H2 pressure, purity and temperature performance of seal oil system and stator water cooling system. Fill more H2 gas cylinders if pressure and purity are low. If the performance of seal oil system is not satisfactory take corrective measures.

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FIG. 8

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2.33

Increase Load on the Gen. as per loading guide lines upto full rated load 21n MW). Check Gen. wdg/core temp. Gen. T/F wdg. temp. and vibrations. If Gen. wdg./core temp., cannot be controlled by increasing cooling water flow to gas coolers and distillate to stator water coolers. Reduce load.

2.34

If all parameters are within limits, maintain load on the Generator according to boiler and Turbine parameters and conditions. If the vibrations increase beyond limits, reduce load and investigate cause. Check that all the cooler bank fans and pumps are running if not start them. Even then if the temperature of T/F wdg, does not come down, reduce load.

3.

IMPORTANT FACTORS TO BE CONSIDERED WHILE L OADING

3.1

During loading of the turbogenerator, the turbine expansion should be smooth and always on increasing trend.

3.2

Gen. winding temperature and Gen. T/F wdg. temperature should be kept under permissible limits by regulating cooling water flow to gas coolers and running the transformer cooler fans and pumps according to the winding temperature.

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B. 1.

ROUTINE OPERATION AND PERIODIC CHECKS It is important that the generator and its auxiliaries be kept under observation during operation. The annunciation system will give warning of abnormal conditions, but regular observation of different parameters will help the operator to detect any gradual deterioration in the operating conditions and take appropriate corrective action even before any alarm comes. All those parameters should be noted by the operator in the log sheets specially maintained. These are over and above the automatic recording done by instruments. It is recommended that a full inspection of the generator should be made after it has been in operation for approximately one year after commissioning.

2.

HOURS CHECKS:

2.1

TEMPERATURE Hourly checking of temperature of following should be done and any abnormal rise in temperature should be reported to the concerned personnel without delay. Remedial measures should be taken. a)

Stator winding;

b)

Stator core;

c)

Rotor winding;

d)

Cold and Hot gas; (Refer fig. 9)

e)

Distillate temperature and inlet and outlet stator winding; (Refer fig. 10)

f)

Babbitt temperatures of bearing and seal l inser;

g)

Inlet and outlet oil temperatures of generator bearings and shaft seals;

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FIG. 9

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FIG. 10

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h)

Inlet and outlet temperatures of cooling water to gas coolers;

i)

Temperatures of cooling water at inlet and outlet of stator water cooler and seal oil cooler;

2.2

j)

Generator transformer winding and oil temperature;

k)

Unit auxiliary transformer winding temperature

PRESSURES a)

Hydrogen pressure and purity;

b)

Differential pressure of seal oil and hydrogen and pressure of oil after D.P.R.

c)

Seal oil and thrust oil pressure at seals;

d)

Distillate pressure at inlet and outlet of stator winding;

e)

Cooling water pressure at inlet and outlet H2 gas cooler stator water cooler and seal oil cooler;

1.3

f)

Distillate pressure before and after filters;

g)

Oil pressure at inlet and outlet of seal oil filter;

FLOWS a)

Cooling water to H2 gas coolers;

b)

Distillate to stator winding;

c)

Cooling water to stator water cooler and seal oil cooler;

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2.4

VIBRATIONS Vibrations at generator front and rear bearings and exciter and bearing should be noted in axial, vertical and transverse direction.

2.5

SPECIFIC RESISTIVITY OF DISTILLATE Specific resistivity of stator winding cooling distillate should be checked.

3.

DAILY CHECKS

3.1

Surroundings of various equipments should be clean. Care should be taken so that oil or dust does not settle on the insulation of bearings, oil seals, slip rings and brush gear etc.

3.2

Daily gas consumption should be recorded. Any abnormal increase in gas consumption indicates leakage for which necessary corrective measures may have to be taken.

3.3

Check the gas sample to find out whether H2 is leaking into water circuit.

3.4

Examine the condition of H2 drier and reactivate, if necessary.

3.5

Brush gear should be examined for:

: a) Unusual sparking between brushes and slip ring; b) Chattering of the brushes; c) Dust or oil accumulation; Take corrective actions wherever necessary. 3.6

Check for water or oil traces inside stator body. Drain out the accumulated water or oil if necessary.

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3.7

Check the settings of all the electrical pressure gauges and other instruments.

3.8

Check the conditions of the lamps in the signalling system of H2 cooling, seal oil and stator water system.

3.9

Check stator water system for presence of any gas.

3.10

Check the leakage rate of H2 .

3.11

Check the H2 content in oil tank.

3.12

Check the insulation of excitation system.

3.13

Test run the stand by A.C. seal oil pump and the emergency D.C. Seal oil pump. Run them for few minutes to check that they supply oil at the correct pressure and also run smoothly. Check the interlock between two pumps.

4.

WEEKLY CHECKS

4.1

Examine the condition of Brush gear. Replace, if any, short brushes. Check that brushes are freely sliding in their holders. Adjust pressure on the brushes so that it is uniform on all the brushes and is about 1.2 to 1.3 Kg., on each brush.

4.2

Check interlocking between working and stand by stator water pump for automatic take over. Run stand by pump for few minutes to check that it develops correct pressure of water and also runs smoothly.

4.3

Check the operation of automatic D.C. Bridge recorders.

4.4

Check the operation and calibration of Hydrogen purity indicator.

4.5

Check the differential pressure across the filters in the seal oil and stator water system to ascertain whether they are choked or not. If necessary switch over to stand by and take corrective action.

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4.6

Check interlocking between working and stand by H2 cooler booster pump. Test run the stand by booster pump and check flow and pressure.

4.7

Check resistivity of distillate by laboratory testing.

4.8

Check purity of H2 by laboratory testing.

4.9

Check for H2 concentration in bearing chamber.

4.10

Check for H2 concentration in bus duct enclosure.

4.11

Check the gas sample taken from Hydraulic seal for oxygen content.

4.12

Check the bearing vibrations by portable and accurate vibration measuring instruments.

5.

MONTHLY CHECKS

5.1

Check all accessible bolts for tightness.

5.2

Check all the protection and signalling circuits.

5.3

Check that all the alarms operate correctly by simulating abnormal conditions wherever possible or by manually operating the initiating s.

5.4

Check once in three months the polarity of slip rings in order to have uniform wear of the slip rings.

6.

SHUT DOWN CHECKS

6.1

Check insulation resistance of stator winding and rotor winding immediately after shut down. A further check should be carried out immediately prior to starting up.

6.2

Check the calibration of H2 purity recorder.

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6.3

Check the slip rings and brush gear for any abnormality and take corrective measures.

7.

PERIODIC CHECKS

7.1

If required, clean the tubes of gas coolers.

7.2

If necessary, clean the tubes of seal oil and stator water coolers.

7.3

Check the calibration of H2 purity indicators with pure gas or with gas of known chemical analysis.

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C. 1.

OPERATIONAL LIMITS OF GENERATOR - 210 MW CAPACITY OF THE GENERATOR The generator is capable of delivering 247 MVA continuously at 15.75 KV 2

terminal voltage, 9050 amp., stator current and 3.5 Kg/cm (g) Hydrogen pressure with cold gas temperature not exceeding 44°C and distillate temperature at inlet of stator winding not exceeding 45°C. Output of the generator at various lagging and leading power factors are as per the Generator capability curve given in fig.11.

2.

VARIATION OF TERMINAL VOLTAGE Generator can develop rated power factor when the terminal voltage changes within + 5% of the rated value i.e., 14.96 KV to 16.54 KV. The stator current should accordingly be changed within limits of +5%. Permissible voltages of operation and corresponding values of the MVA outputs and stator currents are also to be carefully observed. During operation of the generator at 110% of the rated value of continuous operation, stator current should not increase beyond 9500 amps corresponding to 105% of the rated value.

3.

FREQUENCY VARIATION Generator can be operated continuously at rated output with a frequency variation of + 5% over the rated value i.e. 47.5 Hz to 52.5 Hz. However, the performance of the Generator with frequency variation is limited by the turbine capability.

4.

TEMPERATURE OF THE COOLANTS If the temperature of cooled hydrogen or inlet water to gas coolers increases beyond the rated value, the unloading of the generator has to be carried out. The operation of the generator with cold gas temperature more than 55° C is not permitted. Operation of the generator with cold gas temperature below 20°C is not recommended.

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FIG. 11

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Similarly if cold distillate temperature at inlet of stator winding increases beyond the rated value, unloading of the generator has to be carried out. The operation of the generator with cold distillate temperature more than 48°C is not permitted.

5.

OVER LOADING Under abnormal conditions the generator can be over loaded for short duration. Permissible values of short time over loads in of stator and rotor currents and corresponding duration at rated voltage, rated power factor and rated parameters of Hydrogen and distillate.

6.

OPERATION UNDER UNBALANCED LOAD The turbogenerator is capable of operating continuously on and unbalanced system loading provided that continuous negative phase sequence current during this period shall not exceed 5% of the rated stator current. It implies that maximum difference between line currents is about 10% of the rated value. At the same time current is maximum loaded phase should not exceed the permissible value for given conditions of operation of the turbogenerator under balanced loads. If the unbalance exceeds the above permissible limits, measures should be taken immediately to eliminate or reduce the extent of unbalance to achieve this, then the machine has to be run down and tripped. If negative sequence current reaches a value 20-25% of the rated value, triprelay will operate and the generator will be automatically tripped.

7.

ASYNCHRONOUS OPERATION Asynchronous operation of the generator on field failure is allowed depending upon the permissible degree of the voltage dip and acceptability of system from the stability point of view. During field failure, the field suppression shall be out off from the circuit and active load on the generator shall be decreased to 60% of the rated value within 30-seconds and to 40% in the following 1.5 minutes. The generator can operate at 40% rated load asynchronously for a total period of 15-mts., from the instant of excitation. Within this period, steps

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should be taken to establish the reasons of field failure to restore normalcy or the set should be switched over to reserve excitation.

8.

OPERATION AT REDUCED HYDROGEN PRESSURE Continuous operation of the turbogenerator with Hydrogen pressure inside the stator body lower than the rated value of 3.5 Kg/cm2(g) is not permitted. However, during emergency the generator can be operated at reduced Hydrogen pressure with reduce load continuously and for a short duration as may be the instructions. Within this time action should be taken to restore the Hydrogen pressure to normal value. Operation of Generator in AIR MEDIUM IS NOT PERMITTED.

9.

CAPACITY OF THE GENERATOR WITH ONE GAS COOLER CUT OFF SERVICE The generator can deliver 175 MVA continuously when one gas cooler is out of service. The operation of the generator with more than one cooler out of service is not permitted.

10.

MOTORING ACTION Motoring of the turbogenerator is permissible within the limitations of the turbine.

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D. 1.

EMERGENCY OPERATION Stator Water Flow Low

Check expansion tank level is normal and drains are closed. Check position of recirculation valve Check whether running pump has tripped. Reserve pump should start on Auto, if not start manually. Check differential pressure across the filter is normal.

2.

Stator Water Conductivity High

Check D.M. water conductivity from D.M. plant if nor mal then purge same water from system. If D.M. is tank water conductivity is high then close D.M. make up valve. Check stator water cooler for leakage Regenerate polishing unit resin beds & take it into service.

3.

Hydrogen Pressure Low

Charge

fresh

hydrogens.

If

consumption is high then investigate leaking points. If the pressure persists to drop then reduce load on generator. If the pressure can't be maintained then trip the set.

4.

Hydrogen Purity Low

Purge some hydrogen from casing and charge fresh hydrogen. Check seal performance is normal.

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5.

Seal Oil Differential High/Low

Check DPR is functioning normally. If not change to the by line and get DPR attended. Adjust the pressure at injector/pump discharge.

6.

Liquid in Generator

Open the low point drain of generator and check nature and amount of leakage. Check proper functioning of DPR Check thrust oil pressure Check stator water pressure

7.

Generator Stator

Check gas trap and analyse the gas

Cooling Water Leakage

from it. In case stator water leakage is suspected then shut down the unit and attend the leak.

8.

Damper Tank Level Low

Check DPR operation. If required open the by valve and make up the level, If the level approaches low unit will trip.

9.

Rotor Temperature High

Check gas cooler water flow and cooler inlet/outlet temperature. Check and maintain H2 pres sure. Reduce excitation and load.

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10.

Stator Winding Temperature

Check stator water cooling temp.,

High

pressure, and flow. Check load on unit and reduce if required. Check for hot spots.

11.

Loss of Excitation

Check if unit has tripped and generator breaker has opened, if not do so manually. Check for reason of field failure and correct them.

12.

Generator Transformer

Check load on m/c and ambient temp.

Cooling System Trouble

is normal. Check all cooling fans are in service. Check transformer oil

qua lity and

cooling oil pumps operation is normal.

13.

Generator Roto r Earth Fault.

The set can be allowed to run with careful

watch

over

generator and

excitation parameters. Ask staff to check for the fault & continue to run as per instruction. In case of second rotor earth fault unit trips.

It is not to be

restarted unless the fault is identified and rectified.

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1.

INTRODUCTION

1.1

The Operation Engineer has a very important role to play in power station. He has been given the responsibility of a unit which may cost over Rs.100 Crores. Often the operation engineer has to take decision under time pressure. One wrong decision could lead to shut down of unit for months together the direct/indirect loss due to such shutdown could also go in crores of rupees. So there is a very heavy responsibility on the shoulders of operation engineer. He has to ensure the safety of men and machinery, by keeping supply uninterrupted and at least cost. To achieve all this requires constant effort from the Operation Engineer. But the generation at ANY cost is not desirable. If the operating conditions are such that there is danger to men or machinery, operator must not hesitate to shut down the equipment/machinery. There is often conflict between the need for maintaining continuity of supply and ensuring full safety of the equipment. But the operation engineer must be confident enough to take correct decisions. To achieve this he has to be fully familiar with the details of system, the design limits, the sequence of operation, the interdependence of equipments, unsafe conditions of operation and seriousness of each malfunction. He has to weigh pros and cons and take decision in time. This is possible, if as mentioned, the operator has correct knowledge of operating procedures. He must know WHY he is carrying out certain operations and its implication on the system as a whole. Here are certain important operations and the logic behind them.

2.

AIR VENTS

2.1

Air vents are provided to boiler, heating surfaces, heat exchangers, Main steam lines etc. The proper operation of these vents is essential to prevent any emergency situation later on. For example, precaution must be taken to expell all the air from boiler tubes while boiler filling. For this purpose all the air vents are kept open and boiler filling rate is kept slow. If the air pockets are

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left in the system then it can cause hindrance to fluid flow, and overheating of boiler tubes causing their failure. Care also must be taken while depressurising. The air vents must be opened as the pressure approaches atmospheric air.

3.

CHARGING AND FILLING

3.1

The operations of charging and filling are much the same regardless of the application. The procedure normally followed is:

3.1.1

Open the air vents

3.1.2

Open the drain valves

3.1.3

Start the pump (if the pumps is already in service, open the filling/charging line valve as follows).

3.1.4

Crack open pumps discharge or filling valve until a satisfactory charging flow is obtained (this is usually detected by the sound of the flow through the partially opened valve)

3.1.5

Check that the drain is free from any obstruction and close it.

3.1.6

Expel the air and close the air vent after a steady flow of water has been obtained from it.

3.1.7

While charging, care should be taken to avoid any water hammer. The air must be expelled gradually and completely. To ensure this the rate of charging should be low, this will also avoid overloading of fill pump. The slow charging is also essential to avoid thermal stress where there are temperature differences between the water and the item filled.

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4.

WARMING

4.1

Warming differs from charging is that the ission of warming steam results in the production of large quantities of condensate arising from the warming process. This condensate must be drained away before the lower portion of the pipe can be warmed the precaution also must be taken to carry out this operation slowly to prevent large thermal stresses.

5.

DRAIN VALVE OPERATION

5.1

Due to the tremendous amount of damage which can be caused by maloperation, it is important to know the correct sequence in which drain valves must be operated. Almost invariably drain valves are filled in pairs, two valves in series on the same drain line. The upstream valve (valve nearest to source of pressure) is isolating valve and its companion is the regulating valve. Drain lines should be ission up judiciously, avoiding sudden ission of steam or not fluids which could result is large temperature gradients in the drain lines and possibly 'hammer' or thermal shock.

5.2

We avoid this by charging up slowly, throttling the flow of steam or fluid by restricting valve opening, unfortunately, this introduces another problem; as the age of steam or fluid through the restricted valve opening, creates a phenomenon known as 'wire drawing' or cutting of the valve seats and over a period of time, the valve becomes damaged. To prevent this the valve operation sequence must be as follows : (Refer fig. 12)

FIG. 12

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5.3

Operation

5.3.1

To charge drain line. i)

Crack open isolating valve. The small length of drain line between the two valves will be pressurised almost immediately. Wire drawing is virtually nil.

ii)

Open isolating valve fully.

iii)

Crack open regulating valve. This valve is subject to wire drawing charge drain line slowly. Regulate as required using regulating valve only.

5.3.2

To shut off drainage. i)

Close the regulating valve. Wire-drawing takes place as the regulating valve throttles the flow.

ii)

Close the isolating valve. Flow is already zero. So no wire drawing takes place.

iii)

Crack open the regulating valve to release the pressure trapped between the valves & the regulating valve.

5.3.3

As mentioned, the damage due to wire drawing is inevitable but, at least, by using correct operational techniques we can restrict the damage to regulating valve only. This means that we can reasonably expect the isolating valve to give tight isolation when closed, thus preventing losses via ing drains.

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FIG. 13

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6.

DRUM METAL DIFFERENTIAL The boiler drums are filled with water in the bottom and steam in the top due to which the cooling and heating rates vary between the top and the bottom. This results in temperature differences between the top and the bottom. Stress analyses show that the principal criterion for reliable rates of heating and cooling should be based on the relationship between the temperature differential through the drum wall and the temperature differential between the top and the bottom of the drum both measured in same circumferential plane stress analysis also show that the allowable temperature differentials are based on tensile strength, drum diameter, wall thickness, and pressure; therefore, each steam drum has its own allowable temperature differential curves, one set for cooling and one set for heating. To keep the thermal stress values within the limit, operation engineer must ensure that under all operating conditions the actual temperature differential is below the allowable temperature differential. Normally the temperature differential should not exceed 50°C. (Refer fig. 13).

7.

DRUM GAUGE GLASSES

7.1

These give direct measurement of drum level. Normally 2 gauge glasses (sometimes 3) are provided to boiler drum. It must be ensured prior to light up that gauge glasses are available for service and are in charged condition. 2

Especially, during cold start, the remote indication is above 10 Kg/cm . Also during light up operation there are large drum level fluctuations. An about 5 to 10 Kg/cm2 the gauge glasses should be blown from water and steam side to clear of any dirt blocking the ports. As per IBR boiler must not be operated with all the gauge glasses provided out of service.

8.

FLAME INSPECTION

8.1

In a unit operation, boiler is likely to give more trouble than turbine and generator. In boiler, it is observed that troubles due to combustion are more compared with others. So it is necessary to ensure always that combustion in boiler is taking place properly. Besides check on flue gas analysis, the visual

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inspection of boiler flame can give where as to whether the combustion is satisfactory or not. 8.2

An oil flame should be yellow and clear with no smoke. As the flame temperature increases the combustion efficiency increases. A yellow flame indicates that oil is releasing the greatest amount of heat energy. A short, white flame or a red, smoky flame indicates lower temperature and a lower efficiency. A white flame indicates too much air and a red flame indicates too little air. Therefore, for a good oil flame, air fuel ratio, air distribution and oil viscosity must be proper. The gun tip orifices must be kept clean.

8.3

The efficient coal combustion also produces a yellow flame, the flame should have an even, regular shape. An uneven flame indicates fouling of the burner nozzles.

9.

SCAPH - OPERATION

9.1

When lighting up the boiler from cold state, since most of the furnace is relatively cool large amount of heat is absorbed in the furnace. This reduces the flue gas temperature leading the boiler. The fuel oil which is fired for light up has 1.5 to 3.5% sulphur depending upon the quality. This sulphur forms SO3 after combustion and combines with H2 O to form highly corrosive Sulphuric acid when temperature falls likely when lighting up the boiler from cold state. Due to large % age of sulphur in oil, special care must be taken when oil is being fired. The sulphuric acid thus formed corrodes portion of an heater and sometimes economise tubes also to prevent this cold end corrosion heat transfer in air heater is minimised by raising the air, temperature going to air heater. This is done by putting steam Coil Air Pre Heater at the discharge of F.D. Fan. Steam is ed thro' SCAPH when heavy oil is being fired which raises the temperature of air going to air heater and flue gas temperature in air heater remain high. When boiler gets sufficiently warm up, the flue gas temperature at the exit of air heater starts increasing then gradually steam supply to SCAPH is cut off keeping watch on A.H. gas exit temperature.

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10.

BOILER EXPANSION MEASUREMENT Normally for all utility boilers (i.e. power station boilers) the entire boiler, casing and insulation are suspended from top. The provision for free expansion for all parts of the boiler is important but in the case of furnace tubes it is vital. Since the boiler is suspended from the boiler house steel work, the expansion is mostly in downward direction. On a typical 500 MW boiler, the total expansion from cold to full load can be as high as 340 mm. Expansions, in other directions are also significant of the order of 70 to 80 mm. The boiler must be allowed to expand freely in all directions. Scales are provided at different elevations to measure the expansions. Readings must be taken and free expansion must be ensured. This is very important especially when the boiler is being taken into service after major shut down because it is likely that during shut down some temporary piping, scaffolding was welded with the boiler structure.

11.

ECONOMISER RECIRCULATION VALVE During pressure raising period, very little amount of water es through the economiser and there is a danger of the economiser overheating, and in extreme cases, vapour locking. To prevent this condition the economiser recirculation valve is kept open during the pressure raising period. The recirculation in economiser takes place in similar manner as in water wall tubes. Once a steady flow is established to the drum, economiser recirculation valve can be closed.

12.

BOILER WATER TREATMENT The trend toward higher pressures and temperatures in steam power plant practice imposes a severe demand on boiler water quality to maintain steam purity for elimination of trouble some solids in the steam. Direct treatment of boiler water, usually referred to as internal treatment, is used 1) to prevent scale formation caused by hardness constituents, and 2) to provide PH control to prevent corrosion, treatment that is inadequate or incorrect in either aspect can lead to tube failures and result in costly unscheduled outages. The permissible limits as contaminants entering the boiler and also treatment

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chemicals that can be added to the boiler decrease with rising boiler pressures. (Refer fig. 14). Normally hydrazine is added to feed water to control its oxygen, content. Presence of oxygen beyond permissible limits leads to corrosion of the boiler tubes. Sodium phosphate (usually tri-sodiumphosphate, Na 3 PO4) is used to control the total dissolved solids in boiler water and its PH value. However, the care must be taken not to over doze these chemicals in boiler water as this will also prove harmful to boiler tubes. Maintaining dissolved solids at the level required to prevent foaming requires continuous or periodic blow down of boiler water. The proper treatment of boiler water for high pressure boilers will ensure safe and efficient operation of these boilers.

13.

BARRING GEAR When shutting down hot machine or before turbine start up the turbine must be on barring gear. When a turbine is shut down; due to its heavy weight, high temperature and uneven cooling the turbine rotor will have permanent deformation (hogging/bending). So the main function of the barring gear is to promote even cooling of the steam rotors and cylinders when turbine is shut down. The barring gear is engaged immediately after turbine becomes standstill following a trip. It is safe to carry out this operation locally, though remote start provision is usually provided. The barring speed is usually low (3 to 4 rpm) but high speed barring gears (about 200 rpm) are also common. The provisions of high speed barring gear enables to bring the turbine off barring gear with minimum steam ission while rolling the turbine.

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FIG. 14

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14.

SOAKING OF TURBINE Depending upon the type of the start up (cold, warm, hot), turbine is soaked at some particular RPM for predetermined time interval. During soaking period turbine speed is held constant and steam parameters kept steady. Care should be taken to see that soaking speed is not near critical speed (Turbine manufacturer's recommendations to be followed). Soaking helps in bringing differential expansions within limits, also the operator gets sufficient time to check up other turbovisory parameters like turbine expansion, turbine vibrations, bearing drain oil temp, drain oil flow etc. After satisfying himself of healthiness of turbine he can proceed for further rolling of turbine. The soaking time is more for cold start compared to warm and hot start.

15.

CRITICAL SPEED When shaft or rotor, revolving in bearings, speeds up to where centrifugal force tending to whip it sideways just balances the elastic stiffness tending to keep it straight, the slightest mechanical unbalance builds up a whirling motion, which may be of destructive amplitude. The rotor then is revolving at critical speed. this phenomenon is due to the resonance frequency when the rotation speed corresponds to the natural frequencies of lateral vibration of the rotor. It is inadvisable to run any rotor at or near critical speed for any length of time regardless of perfection of balance. The operation engineer must be well aware of exact critical speeds of the turbine. Care must be taken NOT to hold the turbine speed nearby critical speed value and the speed rise should be kept uniform without any interruption.

16.

MONITORING OPERATION PARAMETERS As the continuous of power is essential, the operator must also keep in mind to generate the power at highest possible efficiency. The efficiency and reliability go hand is hand especially at operation stage. As the pressure temperature limits are stretched to maximum, even a slight increase of these parameters could be detrimental for the unit even the deeper condenser vacuum compared to the designed value is not desirous: So the operation engineer must strive to keep the operating parameters within the specified

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limits but close to these limits. Besides by monitoring parameters like make up water consumption, auxiliary power consumption, fuel oil consumption etc., operation engineer can drastically reduce the cost of generation. More make up water consumption not only results in loss of costly D.M. water but also the heat associated with it. More auxiliary power consumption and more fuel oil consumption normally takes place when the unit is operating at part load. The reasons for part loading must be identified and rectified immediately. The operation engineer has a big role to play here.

17.

USE OF COMMON AUXILIARIES

17.1

In a station consisting of number of units, there are many auxiliaries common to all the units. So far the operation engineer it is essential to know how the adjacent units will be affected by his operation. For example, aux. steam supply, fuel oil supply, compressed air supply, cooling water supply, reserve power supply etc. are common for the units. Now if a unit is to be started, before charging say aux. steam header from adjacent unit. They should be informed about this so that in case of any problem it can be immediately sorted out without creating any emergency. If not given prior notice, the unit controller of adjacent unit will have less time to correct the fault developed and this can endanger the operation of his unit. To prevent such mishaps proper communication must be maintained between the units especially while using common auxiliaries.

17.2

Proper use of instruments:

17.3

As the unit sizes are going on increasing, more and more operation is carried out from remote. For an operator in UCB, therefore it is very important to have correct knowledge of system parameters. For this purpose there are large numbers of meters, graphs and other instruments provided in UCB.

17.4

For one parameter there could be more than one instruments available n i UCB (e.g. drum level, steam temp. furnace draft etc.) The operator should see that the readings in such instruments are matching within reasonable limits. In case of any discrepancy the operator should not take convenient correct reading for granted, instead should believe the worst reading as

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correct one and investigate the matter. If the result of such investigation proves that there is fault in the instrument, then it should be got rectified from maintenance department immediately. For other parameters also (where only one instrument is provided in UCB for indication) in case of any deviation from standard value, the matter must be investigated and instrument fault must be attended.

18.

SHIFT ROUTINE

18.1

It is observed that large number of mishaps in power station operation take place at the time of shift change over. This shift change over period is such that operator tends to take things easy after days work-out or he is busy in writing log book. So there are chances that he may overlook certain operational parameter going astray. Similarly when some operator takes over the charge, then he is busy in reading the logbook of previous shift. He also may overlook the faulty parameter. Under such circumstances emergency situation can arise. It is important for operation staff, therefore, to take care for avoiding such situation. The logging of each event should be done immediately after it occurs with all the details including the remedial action taken. The logging should by systematic. At the time of charge hand over, the incoming operator should be briefed about various important operations in the shift especially if any abnormal situations had been handled. The problem areas that can endanger unit working or can cause load reduction must be briefed to incoming operator. The status of standby auxiliaries must be mentioned in the logbook. This systematic approach taken while shift change over can, therefore, help in performing better and better. At the same time during the shift also the operator has to be vigilant, so that the unit generation is kept at optimum level. Here, also, the systematic approach can be very productive.

18.2

The following shift routine should be made at intervals within each shift and at the commencement of each shift.

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18.2.1

Main A.C. Circuits: Note the position of: i)

220 KV/400 KV bus bar distribution, distribution of feeders, generator and station transformers / such questions should be asked: Does one unit feed any particular grid line? What happens if any grid line feeder on machine trips to the overall position?

ii)

Auxiliary supply position. The position of interconnectors of H.T. and L.T. supply.

iii)

Note whether the unit is on station or unit supply for HT and LT systems.

18.2.2

Boiler Feed System: Note the feed pumps on load and if the standby pumps are available. Observe whether they are selected to auto or manual. i)

Drum level control - is it on auto or manual.

ii)

Which feed line is charged and the position of standby feed line.

iii)

Note the availability and condition of standby condensate extraction pump.

18.2.3

18.2.4

Tank levels: i)

Inspect all tank levels.

ii)

Check also the levels for F.O. tanks D.M. make water tanks etc.

Mills: Examine mill system: i)

Check which mill systems are on load and the position of standby milling systems.

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ii)

Note mill temperature and see whether controls are on auto or manual.

iii)

Examine P.A. fan differentials and see whether they are on auto or manual.

iv) 18.2.5

18.2.6

Check R.C. feeder controllers - see whether on auto or manual.

Combustion Control: i)

Check whether furnace draft is an auto or manual.

ii)

Check whether oxygen control is an auto or manual.

iii)

Check furnace draft reading.

Turbogenerator: Note: i)

Which ejector/air pumps is in service and the position of standby.

ii)

Extraction pump on load and position of standby.

iii)

i)

Auxiliary oil pump

ii)

D.C. Emergency oil pump.

iii)

Turning gear oil pump

Auto or manual selection.

(if provided) iv)

Availability of A.C. and D.C. seal oil pump and auto manual selection.

v)

Stator water pump in service and protection of standby pump.

vi)

Generator transformer oil pump and intercooler water pump on load and whether standby available and auto/manual selection. The reasons why any plant is not as auto should be determined.

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18.2.7

Efficiency Control: Particular attention should be given to following item to monitor efficiency. (i)

Ensure that all parameters are at their correct valves. Load in particular must not be lower than suggested by grid contro1.

18.2.8

(ii)

Examine milling and combustion. Ensure that they are in good order.

(iii)

Examine D.M. water consumption.

(iv)

Check total auxiliary power consumption.

(v)

Check condenser vacuum.

Statutory Requirements: i)

Check static condition for grit emission and smoke density. Where these are continuously monitored and each fitted with alarms, this problem is eased.

ii)

Check C.W. conditions to ensure that statutory consents are being observed. Note cooling tower emission.

18.2.9

Miscellaneous: i)

Check all bearings and glands for any of abnormality.

ii)

Check oil level of bearings and see that lubricating oil rings on journal lub. oil is clean if in doubt change.

iii)

Inspect for fresh oil leaks. This will be easy if the plant is clean and almost impossible if it is dirty.

iv)

Check transformer oil levels.

v)

Check fire fighting equipments.

vi)

Check state of change of station batteries (quick/tuckle)

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vii)

Check state of lighting - particularly emergency lighting.

viii)

Attend to steam, water and coal leaks wherever possible.

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1.

INTRODUCTION The modern 500MW unit steam generator is equipped with a comprehensive FSSS which allows the furnace purging and starting of fuel firing system at a predetermined sequence when the set preconditions, as outlined in FSSS logic diagrams, are satisfied. The exhaustive preconditions, if not satisfied, does not allow equipment to be started hence safeguarding the equipment along with the safety of the operating personnel. Following procedures for lighting up and loading the boiler has been discussed keeping in mind all those interlocks & protection as prescribed in FSSS. Sequential startup of boiler from light up to full load is first described followed by various operational care of boiler during its operation.

2.

COLD START-UP AND LOADING PROCEDURES For lighting up the boiler and loading it further till it reaches its rated capacity, proceed as follows:

1.

Ensure that all the boiler pre-start checks have been carried out.

2.

Check that the boiler is filled to normal water level with suitably treated feedwater.

3.

Check the unit control desk and control s and ensure that all equipment and indications are satisfactory.

4.

Check that the fuel oil system has been put into service and ready for fuel oil firing.

5.

Check that atleast 2 circulation pumps are in operation and third kept as standby.

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6.

Ensure that the two secondary air-preheaters are in service with their gas and air side dampers open. It should be noted that for starting purposes one air preheater is also sufficient but that will allow only upto 5 mill operation.

7.

Start up the two primary air preheaters, if both are available. One air preheater will only allow upto 5 mills to be started.

8.

Check that both ID and FD fans are in service. The furnace draught should be maintained at about-8mmwc and the total air flow should be adjusted by controllling the FD fan blade pitch angle until the flow is 30% MCR. (about 630t/hr.)

9.

When the fans are started, the secondary air damper control (on "AUTO") should modulate the auxiliary air dampers to maintain a programmed set point differential between the windbox and furnace. Note: Upto 30% BMCR the wind box furnace diff. pressure will be maintained at 40mmwc. It will then be started to close with load until it is 100 mmwc at 60% BMCR. It will then remain constant till full load.

10.

Startup the duty flame scanner air fan.

11.

Ensure that the steam coil air preheaters are placed in service.

12.

Check that there has not been any fuel oil leakage into the furnace.

3.

CAUTION OIL LEAKAGE INTO THE FURNACE CREATES A POTENTIAL EXPLOSION HAZARD. DO NOT PROCEED UNTIL AFTER ANY LEAK HAS BEEN STOPPED AND OIL CLEARED.

13.

Initiate and carry out the furnace air purge prior to firing the first oil burner.

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14.

Check that the burner tilts are in the horizontal position.

15.

Select the first oil burner to be fired and start up the burner. Normally when starting from cold, bottom level oil burner (level AB) are taken into service.

16.

After firing any burner check for satisfactory ignition as follows: i)

Check flame monitor indication shows "Flame in”

ii)

Visually check flame through local viewing doors using suitable eye protection until four oil burners are established. If ignition is found unsatisfactory take out the burner from service.

17.

When the first oil burner is established fire the other three oil burners in the selected level, one at a time allowing combustion conditions to stabilise before firing the next burner.

18.

Check the air flow, furnace pressure and combustion conditions and adjust controls as necessary to maintain furnace suction at about 8 mmwc and the total air flow at 30% MCR rate (630 t/hr.)

19.

When conditions are suitable place the furnace draught controls on auto.

20.

When the steam issues under pressure from the header drains close all superheater drains so that all steam generated es through the superheaters. All superheater drain valves should be given a 20 second blow every half hour until the boiler is on load to remove any accumulated condensate. Check the drain temperatures when blowing.

21.

When the drum pressure shows about 2 kgf/cm2g and continuous steam starts issuing out, close all drum A superheater vents.

22.

Maintain the drum water level within the normal working limits of plus 100 mm and minus 100mm at a times during the cold starting procedure.

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If it is necessary to add water to the boiler use the running feed pump and low load feedwater line for feeding. 23.

During the boiler pressure raising and initial loading period carefully monitor the relative operating parameters of the plant.

24.

Monitor the rate of boiler pressure increase. This must not exceed a corresponding increase in saturation temperature of 100° K/h.

25.

Monitor the drum, superheater and reheater tube metal temperatures. They do not exceed the given limits.

26.

Monitor the furnace gas temperature. This must not exceed 540° C until steam is ing through the reheater tubes. i.e. HP- LP by cut

in.

Initiate the operation of the furnace temperature probes when the burners have been fired. 27.

Monitor the rate of increase of the superheater outlet steam temperature. This must not exceed 5° K/min. Refer to the recommended temperature raising curves.

28.

Monitor the rate of increase of the reheater outlet steam temperature when flow is established through the reheater tubes. This must not exceed 10°K/min.

29.

Continue raising the boiler pressure at the required rate, maintaining checks on the drum water level, boiler expansion etc.

30.

During start-up of the unit the drain system serving the back (steam cooled) walls may be used to control the final superheater outlet steam pressure and temperature in case HP-LP By is not in service. Opening the back drain valves preferably in steps will cause a reduction in the unit pressure, an increase in firing rate to maintain pressure provide a subsequent increase in

the

superheater outlet steam

temperature.

EXERCISE CARE NOT TO EXCEED THE FURNACE EXIT GAS

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TEMPERATURE LIMIT OF 540°C. Modulating the steam pressure and temperature by this method permits the unit to attain the highest possible superheater outlet temperature approaching the turbine metal temperature on a hot restart or 55° of superheat during a cold start. NOTE: Drain valves should be either open or fully closed not throttled.

4.

CAUTION All by drain valves must be closed immediately after the unit is synchronized.

31.

The burner tilt angle should be adjusted as found necessary to obtain the required pressure and temperature relationship before starting the turbine.

32.

Before starting up the turbine the steam main must be warmed up and charged to suit the turbine requirements.

33.

With steam ing down the main steam drains it will be possible to close in and eventually fully close the superheater outlet drain and start up vent.

34.

When the turbine start-up conditions are obtained, select and fire two more oil burners ready for the extra steam demand.

35.

When the feedwater flow to the boiler reaches the capacity of the low load line, one of the heavy duty lines should be placed in service.

36.

With a constant economiser feedwater established close the economiser recirculating lines isolating valves.

37.

Prior to synchronising and initial loading fire one more oil burner in the second level (CD) ready for the extra steam demand.

38.

When the turbine has been synchronised ensure closure of all the isolating valves of drains and vents.

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39.

After the turbine has been synchronised continue raising the boiler load and main steam and reheater pressure and temperature to suit the turbine requirements. At about 20% BMCR drum level 3 element control may be put on auto. Now preparation should be made for starting up the first coal mill as described below.

40.

Start to warm up the primary air heaters ready for use as follows : i)

Open the gas inlet and outlet isolating dampers.

ii)

Gradually open until fully open the gas inlet dampers.

41.

Select and start up the first P.A. fan.

42.

When the fan is running open the outlet damper.

43.

Startup the second primary air fan and then open the outlet damper. Before starting second PA fan ensure that both primary AH and FD fans are in service.

44.

Place the P.A. fans on auto control.

45.

Place the P.A. fans steam coil air-preheaters in service.

46.

De-isolate the air side of the primary air-heaters as follows: i)

Open primary air heater A air outlet isol. damper.

ii)

Open primary air heater A air inlet damper.

iii)

Open primary air heater B air outlet isol. damper.

iv)

Open primary air heater B air inlet damper.

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47.

When boiler load and operating conditions are satisfactory, the first coal mill should be made ready for starting. Ensure that all mill starting requirements have been checked. The first mill will be started when turbine load above 22% and other parameters as per the startup curves.

48.

Initiate the start of the selected mill.

49.

When the mill start up sequence is completed initiate the start of coal feeder.

NOTE:

If the unit start up follows a Master Fuel Trip the pulverizer may not be empty. It must be operated to clear it of excess coal before starting the feeder. During this procedure the pulverizer valves of all other idle pulverizers must be closed in order to prevent blowing hot furnace gases back into the idle pulverizers and coal piping. When most of the coal, has been removed from the pulverizer, the feeder can be started at minimum speed and then adjusted to a speed selected to give a stable flame or as required to meet unit load requirements. Do not it hot air to the pulverizer until the feeder is started. Be sure that the ignition energy is established before starting the pulverizer.

50.

Ensure that satisfactory ignition of the coal burners is obtained and check that the combustion is satisfactory as follows : i)

Visually check flame if considered necessary through local viewing doors.

5.

CAUTION

ENSURE SUITABLE EYE AND FACE PROTECTION IS USED. ii)

Check the flame monitor indications. "Flame in" should be indicated on the applicable level.

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iii)

iv) 51.

Check the flue gas oxygen, this varies with load as follows : 100% to 80% BMCR

:

3.5%

60% BMCR

:

5%

Below 60% BMCR

:

above 6%

Check the flue gas CO. Maximum reading range 15% - 20%.

When the pulverizer is proven in service the fuel air dampers would open automatically to maintain good combustion. Maintain the fuel feed at a minimum consistent with stable ignition. Operate the F.D. fan blade pitch control as required.

52.

Check the mill outlet temperature. Adjust the control set point as necessary to maintain the required operating value between 70°C to 80°C. At no time should this temperature exceed 93°C.

NOTE :

Pulverizer startup will cause a sudden and sharp increase of steam pressure. This will level out rapidly as load is increased in the turbine.

53.

When the mill is satisfactorily established the oil burners in service can be reduced in the elevation associated with the mi ll in operation.

54.

Adjust the loading of the mill to obtain the required rate of boiler load increase as per the required boiler pressures and temperatures to suit the turbine requirements.

55.

Place the electrostatic precipitators in service.

56.

When the required load (40% turbine load) conditions are obtained prepare to start the second coal mill. Ensure that all the mill starting requirements have been checked before starting the select second mill.

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The second mill to be started should be preferably adjacent to the first mill in service or the firing oil burners, eg. mill B. 57.

When the mill is in normal operation and furnace combustion has stabilised above 40% the combustion control may be put on auto.

58.

At about 50% turbine load the third mill may be cut in as per the steps 48 to 54.

59.

Continue to adjust the loading of the mills as required using the mills master to obtain the required rate of boiler pressure and temperatures to suit the turbine requirements.

60.

61.

Place the air flow controls on auto as follows: i)

Place F.D. fan A control damper on auto.

ii)

Place F.D. fan B control damper on auto.

iii)

Place F.D. fans master on auto.

iv)

Place the combustion air master on auto.

v)

Place the oxygen trim DV on auto.

vi)

Place the oxygen trim on auto.

With three mills in service and the air flow controls on auto the mills master should be made ready to be placed on auto control.

62

Set the steam pressure to desired value, the same value as the measured value by raising the pressure gradually.

63.

Place the mills master on auto.

64.

Place the boiler master on auto.

65.

When the boiler load is about 50% the overfire air control (for regulating NO X at the minimum level) should be placed on auto as follows: i)

Select the overfire air damper lower to auto.

ii) Select the overfire air damper upper to auto.

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The effective starting load, however, must be determined during initial unit operation. 66.

Continue raising the boiler load at the required rate the target load control on manual. For getting the 4th, 5th and 6th mills, the following general guidelines may be used (cold startup only).

67.

No of Hills

Turbine Load

Fourth

60%

Fifth

70%

Sixth

74%

As each pulveriser is placed in service the required associated ignition energy must be available. When the unit firing conditions are stabilized all warm up oil guns may be withdrawn from service.

68.

With six mills in service and the boiler at operating pressure, the boiler load can now be increased to 100% turbine load as required following the loading curves.

69.

When the boiler load is above 60% and the reheater steam temperature is close to the normal operating level of 540°C the controls should be placed on auto as follows: i)

Set

the

reheater

temperature

desired

value

(nor

operating

temperature is 540°C) ii)

Place the burner tilts on auto.

iii)

Select one line spray control valve in RH desuperheater control station (LHS) for duty and place on auto.

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iv)

Select one line spray control in RH desuperheater control station (RHS) for duty and place on auto.

70.

When the boiler load is above 60% and the superheater steam temperature is close to the normal operating temperature of 540° C the controls should be placed on auto as follows: i)

Set the superheater outlet temperature desired value to the level (normal operating temperature is 540°C).

ii)

Select one line superheater spray control valve in the SH desuperheater control station (LHS) for duty and place on auto.

iii)

Place the LHS superheater spray master on auto.

iv)

Select one line spray control valve in SH desuperheater control station (RHS) for duty and place on auto.

v) 71.

Place the RHS superheater spray master on auto.

At a suitable time during the loading period carry out a full sootblowing operation. It may be necessary to soot blow the primary and secondary air heaters soon after placing in service depending on the quantity of soot deposition.

72.

During the boiler loading period maintain a close check on all the boiler operating condition. Ensure that the design limitations are not exceeded in any case.

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1.

NORMAL OPERATION - UNIT LOAD CHANGES During normal operation, with the unit on the line changes in pulverizer loading and/or the number of pulverizers in service may be required to accommodate unit load changes. A wide range of load control can be achieved with the pulverizers on auto.

a.

Decreasing Load If the unit load decrease to a point where the feeder rating of the pulverizers in service is reduced to 40% of maximum, a pulverizer should be taken out of service. This can be a pulverizer serving either an upper or lower coal elevation, at the discretion of the operator. To remove the pulverizer from service, proceed as follows: i)

Start the ignitor and warm up oil guns associated with the coal elevation served by the selected pulverizer.

ii)

Gradually reduce the feeder speed of the selected pulverizer to minimum.

iii)

When the feeder rating is at minimum (approximately 25%) close the hot air shut off gate.

iv)

Allow the pulverizer coal-air temperature to drop to 50°C and take feeder out of service.

v)

Allow the pulverizer to run for atleast two minutes to insure that it is completely empty, then stop the pulverizer.

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vi)

The associated ignitors and warm up oil guns may be shut down when furnace conditions have stabilized.

Every effort should be made to keep adjacent pulverizers in service. If, due to maintenance, a pulverizer is not available skipping the coal elevation served by the pulverizer is permissible. Skipping of two coal elevations is not recommended and is only permissible with the use of auxiliary ing fuel (Warmup guns). If the unit load is reduced to a point where only two pulverizers are required, auxiliary ing fuel (warmup guns adjacent to the coal nozzles in service must be placed in service to assure positive ignition when the feeder rating drop to 50% or less. Note:

Auxiliary ing fuel should be used at any time and under conditions in which, the operators judgement, stabilization is necessary.

b.

Increasing Load If after a load decrease where pulverizers have been taken out of service, the unit load should increase to a point where the feeder rating of the pulverizers in service exceeds 80% of maximum, an additional pulverizer should be placed in service as follows: i)

Establish the ignition energy required for the coal elevation served by the selected pulverizer.

ii)

Start the pulverizer.

iii)

Open the hot air shut off gate and bring the pulverizer up to operating temperature.

2.

CAUTION Prevent possible water damage to the turbine by using extreme care to eliminate all water from the main steam line, cold and hot reheat lines and superheater and reheater elements and headers before the turbine is rolled.

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i)

Initiate a furnace purge and normal light off sequence of the igniters and warm up oil guns.

ii)

Close all reheater vents and atmospheric drains before pulling a vacuum in the condenser. Reheater condensate drains may be left open until the turbine is under light load.

iii)

When steam is itted to the turbine for rolling it is desirable to have a minimum steam/turbine metal temperature differential. This can be achieved by firing at a maximum rate within the furnace exist gas temperature limitation of 540°C. In order to reach the exit gas temperature limit, it may be desirable to start a pulverizer at this time. Stabilize the firing conditions to maintain the maximum furnace exit gas temperature without exceeding it.

During a hot restart, the turbine metal temperature will normally require a rapid reloading of the unit.

3.

CARE DURING BOILER OPERATION

A.

General

a)

Before starting up the boiler and at each extended outage the economiser should be inspected externally and if necessary cleaned. After overhauls, accumulation of erection material (wood, insulation, welding rods, etc.) is not unusual. Large debris should be removed manually, followed by washing down the economiser banks by means of a hose and water.

b)

Any exposed insulation should be kept in good condition at times.

c)

Access doors should be bolted tight. Check the doors occasionally for tightness.

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d)

The frequency with which soot blowers are used depends entirely on local conditions. When the economiser is first placed in operation, the economiser soot blowers should be blown about once every shift. Observation of the increase in draft loss between blowings will determine how long an interval may be set as a standard. In many cases it has been found that blowing the economiser soot blowers once a day or less is sufficient.

e)

While the boiler is being brought up to pressure, provision should be made for gradually heating and adequately draining all cold steam piping from the beginning by opening all drain valves and by (if stop valves are provided).

f)

During initial firing, periodically check the expansion movements of the boiler and make sure the casing, heaters and piping move freely with respect to the structural steel. Expansion markers should be installed at suitable locations to facilitate inspection. Periodic checks should be made during the life of the unit to determine that expansion movement continues to occur in a normal, uniform manner. All hangers on the unit and related piping should be checked periodically for proper expansion & .

g)

The ash hopper should be inspected prior to operation of the unit for proper placement and operation of the sluice system. Any condition observed as a potential cause of water quenching of furnace bottom tubes (during normal or abnormal operating conditions) should be corrected.

h)

All inspections should be thorough and comprehensive in every detail. They should be made by competent personnel familiar with boiler operation and maintenance and with water treatment problems. A record of each inspection should be kept in a uniform manner so that results of any change can be compared with former conditions.

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i)

Inspections of tubes, as a result of tube failures or conditions expected to lead to failures, should be even more through. If the cause of the condition is not obvious or cannot be determined clearly such inspections should include metallurgical examinations of tube material, chemical analysis of deposits, etc.

B.

Steam Temperature Control The function of the steam temperature control equipment is to superheat and reheat temperature over the specified control range. Care should be exercised to prevent steam temperatures from exceeding the maximum values especially if steam temperature control equipment is programmed to a boiler rating below the control point. Damage to tubing may result due to localized overheating caused by poor distribution of steam flow at low loads if the maximum values are exceeded. The steam temperature control system at higher loads include the following equipment: a) Fuel and air nozzle tilts (reheat temperature control) b) Spray water desuperheaters (superheat and reheat temperature control)

a

Fuel and Air Nozzle Tilts The fuel and air nozzles can be tilted through a 60-degree (I radian) range, from 30 degrees (0.5 rad) upto 30 degrees (0.5 rad) down. Raising or lowering the flame provides, ineffect, a furnace with an adjustable amount of heat-absorbing surface. The nozzle tilt drive units in the four corners of the furnace should operate in unison (simultaneously) in response to control signals from the reheat steam temperature controller. An increase in reheat steam temperature beyond the control set point moves the tilts down, and a decrease of steam temperature below the set point moves the tilts up in proportional increments.

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A change in unit load will produce, a change in the superheat and reheat steam temperatures. In anticipation of this temperature change a load change signal is usually introduced into the master temperature controller, either from the steam flow or air flow transmitter. This permits the steam temperature controller to initiate corrective action, that is, move the tilts up or down or change the desuperheater water flow, before the temperature change occurs, thereby decreasing temperature fluctuations. When the nozzle tilts reach their minimum tilt and further reheat steam temperature reduction is required, control is automatically sequenced to the reheater desuperheater. b

Spray Water Desuperheaters Reheater desuperheaters are normally provided for emergency use only. They are used for reducing excessive reheat steam temperature when the nozzle tilt control has reached its lower limit. The automatic control signal to the spray water control valves is normally from the same source as the one actuating the nozzle tilt drives. The superheater desuperheaters are normally provided to maintain the design final superheater steam temperature. Desuperheater spray water control is generally a three element cascade system, in which final steam temperature, intermediate (desuperheater outlet) steam temperature and load index (steam flow or air flow measurements) are applied to achieve proper and fast control action.

4.

SHUTTING DOWN OF BOILER

1.

Introduction On a number of occasion boiler and/or its auxiliaries while in operation develops defects/trouble which by itself may not be very serious in nature but

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if left on its own will subsequently cause major failures resulting in plant to remain off the grid for extended periods. On such occasions it is imperative to start shutting down sequence of the unit in a normal way. We will discuss mainly the normal shutting down sequence of boiler & its auxiliaries which at some places will be supplemented with emergency shut down too.

2.

Normal Shut-down of Boiler to cold In shutting down the boiler, the reduction of firing rate is determined by the requirement of the turbine.

1.

Gradually reduce load on the unit, reduce the firing rate in line with the decreasing steam flow. Allow the pressure to drop with reduction in load to accelerate cooling. Reduce the steam temperature of the rate prescribed by the manufacturer but never exceeding the forced cooling rate.

2.

Take "Combustion control" and "SH/RH steam temperature control" on Manual when the load drops to 50% (approx).

3.

When the feeder rating on all associated with the upper most pulverizer in service.

4.

Place the uppermost service pulveriser on manual control. Gradually reduce the feeder rating. When minimum feeder rating (about 25% load) is reached, close the hot air shut-off gate.

5.

When the pulverizer outlet coal- air temp. falls to about 50°C, stop the feeder.

6.

Keep the pulverizer running until it is completely empty. Then stop the Pulverizer.

7.

that the associated windbox dampers get closed and remaining dampers remain modulating by the secondary Air Damper control system.

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8.

When the feeder rating on all remaining pulverizers reaches 40%, take the second pulverizer, supplying the next higher elevation, out of service.

9.

In the same manner continue taking out pulverizers at consecutive lower elevations. When down to 2 pulverisers the adjacent F.O. guns shall be placed in service, prior to reducing the feeder rating of either pulverizer to lower than 50% MCR.

10.

Discontinue ission of overfire air when the unit load has dropped below the predetermined effective starting load. Keep the overfire air dampers slightly cracked open to prevent nozzles from overheating.

11.

Operate all sootblowers.

12.

Reduce the air flow in line with fuel reduction unit 30% of maximum air flow is reached. Further lowering or air flow shall only be done after the fire-out of boiler. Open all auxiliary air dampers and reduce the window to furnace diff. pressure to 35 mmwc.

13.

Check the expansion movement of the boiler as the load is reduced.

14

After the last pulveriser has been shut down, remove the F.O. guns in service.

15.

Open the economizer recirculation valves.

16.

Ensure that SH & RH desuperheater spray water supply block valves are closed.

17.

Purge the furnace.

18.

When RAPH inlet gas temperature falls below 205°C, shutdown the draft fans and air heaters.

19.

Keep one boiler circulating water pump running.

20.

Close atmosing & heating steam supply. Stop F.O. pumps.

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21.

Close MS shut-off valves along with their integral by valves.

22.

Open all reheater vents and drains.

23.

Close CBD 7 stop chemical dosing to the drum.

24.

Break condenser vacuum. When vacuum falls to zero, stop gland seal steam supply.

25.

the operation of steam line and turbine drain valves, as under: a)

Open all drains after HP control valves when diff. temp. between HP control valves and HPT inlet saturated steam falls below 20°C.

b)

Open HP casing drain when HP outer casing (top/bottom) temp. becomes less than 300°C.

c)

Closing of HPT exhaust NRVs causes opening of drains before NRVs.

d)

Open drains before IPT control valves when diff. temp. between IPT control valves and cold reheat steam becomes less than 20°C.

e)

Open drains before extraction NRVs, when the opening of respective extraction NRV becomes less than 5%.

26.

Maintain drum water level near normal adding makeup as required.

27.

Thereafter boiler feed pumps and condensate extraction pumps may be taken out of service.

28.

Open drum vents and superheater vents & drains when drum pressure fails to 2.0 Kg/Cm2 g.

29.

Boiler may be emptied, when the boiler water temperature falls below 95°C.

Note:

During shutting down the boiler special care must be exercised to prevent water from entering the main steam lines, HRH & CRH lines to the turbine

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from any source during and after the shutdown process. This is to prevent possible water damage to the turbine during a subsequent restart.

3.

Possible Sources of Water are:

i)

Overflow from the drum into the SH as a result of high water level.

ii)

Water entering the SH & RH through desuperheaters due to open desuperheater control valves possible valve leakage with the feed pumps running.

iii)

From HP by spray system, due to possible valves ing.

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START-UP PROCEDURE Method of Operation The turbine is started and brought up to speed with the help of main control valves and reheat control valves. Reference speed setter is set to minimum speed at this point if the hydraulic governor is to be used. In this case, the speed reference of the electro-hydraulic controller is set to maximum. For start-up using the electro-hydraulic controller on the other hand, reference speed setter is at maximum and the speed reference of the electro-hydraulic controller is at minimum. The stop and control valves are in the closed position as the trip medium circuit is not yet pressurised. By turning handwheel clockwise or by operating motor of starting and load limit device in the close direction, sprint is auxiliary follow-up of secondary auxiliary medium pressure. Hydraulic converter with follow-up pistons is now in the control valves closed position. As a result, no pressure can build up in the secondary medium circuit when main trip valves are latched in. By further turning handwheel the, valve of starting and load limit device is moved further downwards, whereby control medium is itted first into the start- up medium circuit and then into the auxiliary start- up medium circuit. The start up medium flows to the space above the piston of test values, forcing them down against the action of the return springs. The auxiliary start - up medium raises the pistons of main trip valves, thereby moving them to their normal operating position and permitting trip medium to flow to test valves of the main and reheat stop valves. At the same time overspeed trips and thrust bearing trip are latched in if they have been tripped. During this process, check valve for temporarily cutting off the feed line to solenoid valve from the connection point down stream of filters, while main trip valves are latching with the aid of starting and load limit device for as long as the pressure there is significantly reduced as a result of the high flow of fluid initially required to fill the empty trip medium system. During this time the pressure ahead of solenoid valve is maintained by orifice. This ensures that the solenoid valve remains in the position. The auxiliary start up medium is fed into the auxiliary start-up medium circuit at starting and load limit device from the system down stream of filter (feed during testing as there is no significant pressure there during start up. It is not possible to use medium from this system

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to feed the pressure medium circuit of solenoid valve also, as this would cause too great a pressure drop in the trip medium system while solenoid valves are latching in during testing. Once latching in is completed, the trip medium circuit is closed. Trip medium now flow to the space above piston of main and reheat stop valves and forces it down against piston discs, operation of the starting and load limit device is continued until piston discs reach their lower end position. When handwheel is turned back of motor of starting and load limit device is operated in the open direction the control medium is allowed to drain first from the auxiliary start-up medium circuit and then from the forced upwards by the restoring springs whereby the trip medium flows to the space below piston and slowly drains from the space above piston. The pressure difference thus occuring lifts both pistons together into their upper end positions, thus causing main and reheat stop valves to open. Main trip valves are now held in their upper position by the pressure of the trip medium under their stepped differential pistons. After the stop valves have opened, further turning of handwheel of operation of motor of the starting and load limit device in the open direction will, after ing through a certain dead range, cause lever and sleeve to move downwards, as a result of which the increasing secondary medium pressure above hydraulic converter with follow-up pistons will gradually open control valves. This will run the turbine up to approximately 85 to 90% of rated speed. At this point, hydraulic speed governor will take over and maintain this speed. Starting and load limit device is then set at the maximum position. A pressure gauge and electrical speed transducers are used to measure the speed. Further speed increase, synchronizing and loading of the turbine are accomplished by adjusting reference speed setter. By turning handwheel or operating motor additional tension is applied to speed setting spring, which results in an increase in speed. Since, in interconnected system operation, turbine speed is determined by the grid, operation of the reference speed setter amounts to a load change for the turbine.

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Load Limitation Starting and load limit device acts mechanically on diaphragm of hydraulic speed governor, enabling it to be used to limit turbine load i.e. to limit opening of control valves to a preset value. This setting is made by adjusting starting and load limit device manually or by means of its motor.

Electro-Hydraulic Controller If the turbine is to be started up using the electrohydraulic controller, the reference setter of the electro-hydraulic controller should initially be set to a minimum speed so that the controller takes over run-up of the turbine generator unit as soon as the turbine is operating at a low turning gear speed. When the stop valves have opened, starting and load limit device should be driven into open position, slowly increasing the speed reference of the electrohydraulic controller from its initial setting (minimum) brings the controller into action, bringing the turbine up to rated speed for synchronization. In constant pressure operation after synchronization, the turbine generator unit is loaded up to approximately 15 to 20% of rated output by increasing the speed reference. Further load increased are accomplished by increasing the load reference (brought into control) at this load within the permissible rate of load change. The speed reference if left at a value corresponding to a load out-put of approximately 15 to 20%

Load Rejection On load rejection, i.e. sudden disconnection of the loaded turbine generator unit from grid, the turbine is intercepted by a load rejection control module before it reaches trip-out speed. The resulting sustained speed deviation will be a value corresponding to the drop of the speed controller and the reference speed. During constant pressure operation, this value would be approximately rated speed since during loading the load controller was switched into the circuit at a low load. Naturally, the reference speed may also be reduced to rated speed after a load rejection.

Speed Control

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Speed control may be exercised either hydraulically of electro-hydraulically.

Hydraulic Control Main oil pump supplies the bearing and primary oil circuits with control oil whilst hydraulic speed transmitter acts as a pulse generator for the control circuit, providing a primary oil pressure proportional to the speed. This oil pressure can also be read directly from speed indicator pressure gauge. This primary oil pressure acts on diaphragm of hydraulic speed governor against the force of speed setting spring which is tensioned by reference speed setter. The travel of diaphragm, which can be limited by starting and load limit device, is transmitted by linkage to sleeves of auxiliary follow-up pistons, the pistons of which are held against the medium pressure by spring. Medium drains off according to the amount of port overlap between piston and sleeve and a medium pressure corresponding to the tension of spring is built up. This secondary auxiliary medium pressure acts as a pulse signal via pilot valve of electro-hydraulic converter. Piston of this electro-hydraulic converter assumes a position corresponding to the secondary auxiliary medium pressure and operates the sleeves of follow-up piston via a linkage system. A system stabilises the piston of pilot valve and piston of electro- hydraulic converter. As already described for auxiliary follow-up piston a secondary medium pressure corresponding to the position of the sleeves and to the related spring tension builds up in the follow- up pistons of electro-hydraulic converter. Any change in the position of linkage results in a proportional change of the secondary medium pressures ' in the follow-up pistons of the electro-hydraulic converter. The secondary medium circuits and the secondary auxiliary medium circuits are supplied from the trip medium circuit by way of orifice. The varying secondary medium pressure in the follow- up pistons of the electro-hydraulic converter in turn effects changes in the positions of their associated control valves or other control devices.

Electro-Hydraulic Control The speed of the turbine is measured digitally. For this purpose electrical speed transducers are mounted on the high-pressure end of the turbine shaft.

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The electro-hydraulic converter constitutes the link between the electrical and hydraulic parts of the governing system. The electro-hydraulic converter consists of the speed control converter and a plunger coil system. The signal from the electro-hydraulic controller actuates the control sleeve via the plunger coil system. The control sleeve determines the position of pilot valve in the manner of a follow-up piston. The further mode of action is the same as that of the hydraulic speed governor. Two differential transmitters are located at piston of speed control converter as transmitters to the electrohydraulic controller. This stabilises the control process.

Changeover from Hydraulic to Electro-Hydraulic Control As already mentioned, changeover from one control system to the other is possible even during operation as the two controllers are connected in parallel downstream of the associated follow-up piston batteries, which form a minimum value gate. This means that it is always the controller with the lower setpoint which leads. If the turbine is operated with the hydraulic governor, the speed setpoint of the electrohydraulic controller is set at "Max. speed" which prevents the electro-hydraulic control system from coming into action. To bring in the electro-hydraulic control system, the speed setpoint of the electro hydraulic controller must be reduced slowly until the secondary medium pressures drop slightly. When this occurs the electro-hydraulic controller has taken over. Then, the reference speed setter of hydraulic speed governor is set to "Ma x. speed" the electro-hydraulic is then fully effective and can operate over the entire load range. The hydraulic speed governor also acts as a speed limiter in the event of failure of the electrohydraulic controller. In this case, operation of the turbine may immediately be continued by means of the hydraulic speed governor.

Changeover from Electro-Hydraulic to Hydraulic Control Changeover is performed in the reverse sequence. First reduce the setpoint at reference speed setter until the secondary medium pressures drop slightly. This indicates that the hydraulic speed governor has taken over. Then set the setpoint of the electro-hydraulic controller to maximum. The hydraulic speed governor is then completely effective and can operate over the entire load range.

Adjusting Device for Valves

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An adjusting device which makes it possible to change the time and setting response of the main and reheat control valves is provided for limiting the HP exhaust steam temperature. In normal operation, control medium is itted to the space below the pistons of regulating cylinders by way of energised solenoid valve, whereby the pistons move into their upper and positions against the force of the spring and, via a linkage, tension the springs of follow-up piston of the reheat control valves in such a way that this produces the desired time and setting response of the reheat control valves in relation to the main control valves. For Operation of the plant without the HP and LP by stations, a manual adjusting mechanism is also provided for adjusting the relationship between the valves such that the reheat valves open before the main steam valves. Under these operating conditions, solenoid valve is energised and an interlock is provided to prevent deenergisation. This adjustment may only be performed manually and must always be performed on both follow- up piston batteries, to ensure that changeover from hydraulic to electrohydraulic control and vice versa is possible at all times. This manual adjust must always be reversed before the HP or LP by station is brought into operation.

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WARMING UP AND STARTING UP THE TURBINE CONTROLLERS 1.

Operating

modes

of

the control

system and of the starting and load limit device. Electrical speed control - Warm-up operation

The

turbine

generator

unit

is

accelerated and maintained at constant warm-up speed. - Running up the turbine /generator unit.

Accelerate unit to rated Speed

- Rated speed governor

Maintain unit at rated speed

Hydraulic governor - Warm-up operation

The

turbine

generator

unit

is

accelerated and maintained at constant warm-up speed by manual actuation of the starting and load limit device. - Running up the turbine generator unit

When the reference speed setter in the zero position, the hydraulic governor takes over speed control at approx. 80% rated speed.

So, run-up of the

turbine generator unit from approx. 80 to 100% rated speed is controlled by the hydraulic speed governor. - Rated speed operation

Maintain unit at rated speed

- Over speed trip test

Acceleration to 107% of rated speed by the governor;

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speed

is increased to

163

trip speed using acceleration lever on casing of hydraulic governor; During over-speed

trip

test,

the electrical

speed controller must be disengaged and switched off. Starting and load limit device -

Setting operating con figuration of main

The main trip valves are brought into

trip valves

operating position when the starting and load limit device is in the zero position

-

Opening the stop valves

When the starting and load limit device is in approx 40% open position, the stop valves should be open; the test valves of the stop valves must be in the operating

position

for the opening

procedure. -

2.

Warm-up operation

See Hydraulic speed governor

Electrical Speed Control Control range in % rated speed

0-107% (limitation by hydraulic speed governor)

Set point control -

Target setpoint/actual setpoint

The actual setpoint follows the target setpoint along present gradients.

-

Limitation of setpoint by turbine stress

The

preset

Evaluator (TSE)

according

gradients to

a

is

reduced

predetermined

characteristic to conform to the margin generated by the TSE

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-

Application of the TSE

The TSE signal must always Signal be present if the TSE is not faulted.

-

Operation with TSE faulted

The actual setpoint no longer follows the target setpoint

if

the TSE is

faulted; the actual and target setpoint must be matched up before the TSE signal can be switched off. When the signal from the TSE is not present, the thermal

stresses

in

the

turbine

components must be figured out by comparing tjhe actual temperatures. Limitation by higher-level of alternative controllers or other devices. -

Minimum valve selection

Effective

controller

= controller with

the lowest setpoint setting at any time (also

applies

to

other

devices

influencing the opening characteristics) -

-

Hydraulic speed governor

Limits setpoint by hydraulic minimum

(speed setting device approx. 80%

value selection;

Starting and load limit device

Limit setpoint by hydraulic minimum value selection; excessive control valve opening can be prevented by using the starting and load limit device to limit valve travel.

Operation -

Operating elements and monitoring

See arrangement of control desk.

instruments

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3.

Hydraulic Speed Governor -

Target setpoint/actual setpoint

The actual setpoint immediately follows the target turbine

setpoint (no influence from stress

operation

with

evaluator).

During

the hydraulic speed

governor, the thermal stresses in the turbine

components must be figured

out on the basis of the TSE display or, if the TSE is faulted, by comparing the actual

temperatures

differences

with

and

their

the curves

for

permissible temperature margins. Limitation by higher-level or alternative controllers or other devices. -

Minimum value selection

Effective controller = controller with lowest setpoint setting at any time (Also

applies

to

other

devices

influencing the control characteristic) -

Electro-hydraulic controller 100%

Limits set point by hydraulic minimum value selection.

-

Starting and load limit device

Limit set point by hydraulic minimum value selection.

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START OF TURBINE/GENERATOR (01)

(02)

+

TURBINE/GENERATOR START- UP

PREPARE

+

PREPRATION FOR START- UP

COMPLETED

-----------------------------------------

------------------

EXT. SYSTEMS READY F. OPERATION

CHECK

¶

CIRCULATING WATER CONDENSER

AVAILABLE

¶

COOLING WATER FOR COLLERS

AVAILABLE

¶

AUXILIARY STEAM

AVAILABLE

¶

OPERATIONAL WATER SUPPLY

AVAILABLE

¶

CONDENSATE SYSTEM

READY FOR OPERATION

¶

VACUUM - PUMP

READY FOR OPERATION

¶

THE EXTERNA L SYSTEMS DO

¶

NOT BELONG TO THE SCOPE

¶

OF SUPPLY (TURBINE/GENERATOR).

¶

POSITION OF VALVES

¶

ACCORDING TO SINGLE LINE

¶

DIAGRAMS OF SYSTEMS

¶

INSTRUCTIONS OF EXTERNAL

¶

SYSTEMS MUST AGREE WITH

¶

TURBINE OPERATION

+

+ (03)

+

EXTERNAL SYSTEMS

READY FOR OPERATION

------------------------------

-----------------------------------

OIL SYSTEM AND TURNING GEAR

START

¶

START OF OILSYSTEM APPR. 6 HRS

¶

PRIOR TO TURBINE START.

¶

EXTEND TIME IN ADVANCE OF

¶

TURBINE START IF OIL

¶

TEMPERATURES ARE EXTERMELY LOW

¶

WITH FGA (OILSUPPLY)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

© PMI, NTPC

167

-

(04)

FGA=FUNCTIONAL GROUP

¶

AUTOMATIC

CF-RECONDITIONING PLANT AND HEATERS

IN OPERATION

¶

PRIOR TOP CONTROL PUMP

¶

OPERATION THE CONROL

¶

FLUID TEMPERATURE SHOULD BE

>20 0 C

¶

TEMP. – RATE DURING HEATER OPR.

1-2 K/M

¶

START OF THE OPERATION OF

¶

RECONDITIONING AND HEATERS

¶

IN ACCORDANCE WITH INITIAL

¶

TEMPERATURE AND HEATING RAT E

¶

OPERATE RECONDITIONING- PLANT

¶

CONTINOUSLY IF NEUTRALIZATION

¶

NUMBER TENDS TO INCREASE

+

TEMPERATURE IN CONTR. FLUID TANK

>20 0 C

+

CONTROL FLUID SYSTEM

START

+ (05)

¶

+

¶

WITH FGA
¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

CONTROL FLUID SYSTEM

IN OPERATION

------------------------------------

---------------------

CONDENSING PLANT

START

¶

TIMING OF CONDENSATE PLANT

¶

START MUST AGREE WITH TIMING

¶

OF FIRST STEAM ENTERING THE

¶

CO NDENSING- PLANT

¶

THE CONDENSING-PLANT DOES

¶

NOT BELONG TO THE SCOPE OF

¶

SUPPLY OF THE TURBINE/

¶

GENERATOR

© PMI, NTPC

168

+

+

+

(06)

¶

POSITION OF THE VALVES

¶

ACCORING TO SINGLE LINE

¶

DIAGRAMS OF SYSTEMS

¶

INSTRUCTIONS OF THE

¶

MANUFACTURER OF THE

¶

CONDENSING- PLANT MUST

¶

AGREE WITH TURBINE

¶

OPERATION

CONDENSING PUMPS ¶

WITH FGA (CONDENSATE SYSTEM)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

VACUUM PUMPS ¶

WITH FGA (CONDENSING PLANT)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

SEAL SYSTEM SUPPLY ¶

WITH SLC (SEAL SYSTEM)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

¶

NOT BELONG TO THE SCOPE

ON

ON

ON

+

VACUUM

< P AMP

+

SEAL STEAM PRESSURE

< P AMB

------------------------------------------------------------

-----------------------------------

+

STATE OF OPERAT. STEAM-GENERATOR

CHECK

+

STEAM GENERATOR

IN OPERATION

------------------------------------------------------------

-----------------------------------

CRITERIA FOR BY - OPERATION

FULFILLED

+

© PMI, NTPC

169

(07)

(08)

*+

+

START OF BY- OPERATION

OBSERVE

------------------------------------------------------------

-----------------------------------

MAINSTEAM – (MS-) LINE

WARM-UP

¶

WITH FGA (TURBINE CONTROL)

¶

WITH FGA (WARM UP OF MS-LINE)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

+ MAINSTEAM – (MS-) LINE

WARM-UP

(09)

+

CRITERIA FOR WARMING- UP TURBINE

CHECK

(10)

+

TURBINE

WARM-UP

+

+

¶

WITH FGA (TURBINE CONTROL)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

TURBINE

WARMED-UP

------------------------------------------------------------

-----------------------------------

CRITERIA FOR SPEEDING UP TURBINE

FULFILLED

/GENERATOR (11)

+

+

+

TURBINE/GENERATOR TO RATED SPEED ¶

WITH FGA (TURBINE CONTROL)

¶

OR

¶

MANUAL OPER. AT OPER. CONSOLE

SPEED-UP

TURBINE/GENERATOR SPEED

3000 RPM

------------------------------------------------------------

-----------------------------------

CRITERIA FOR SYNCHRONIZING

FULFILLED

© PMI, NTPC

170

(12)

+

+

GENERATOR BREAKER ¶

WITH FGA (TURBINE CONTROL)

¶

OR

¶

AUTOMATIC SYNCHRONIZER

GENERATOR

ON

SYNCHRONIZED

OIL SYSTEM AND TURNING GEAR START-UP DIAGRAM (01)

+

SYSTEM READY FOR OPERATION

CHECK

-

MANUAL OPERATED VALVES ACCORD.

CHECKED

TO LIST OF VALVE – POSITION AND IN POSITION -

SPECIAL MANUAL OPERATED VALVES

CHECKED AND IN POSITION

-

¶

VALVE BEF/BEF FANS IN

¶

SERVICE

¶

VALVES BEF / BEH STAND-BY

¶

FANS

SPEC. MAN. OPER. VLVS. OF SYSTEM

OPEN CLOSED

CHECKED AND IN POSITION

¶

RELIEF VALVE OF SHAFT-LIFT

¶

OIL SYSTEM

¶

COOLING- WATER VALVES OF

CLOSED

¶

STAND-BY OIL COOLEER WATERSIDE

OPEN

¶

FILLING-LINE OF STAND-BY OIL-

OPEN

¶

COOLER SOILSIDE

© PMI, NTPC

ADJUSTED

171

+

-

OIL PUMPS

READY TO OPERATE

¶

OIL PUMPS ON MANUAL CONTROL

SWITCH ON

¶

OR

¶

OIL PUMPS ON SUBLOOP CONTROL

OR SWITCH ON

¶

OIL PRESSURE MUST BE

NORMAL

¶

ADEQUATE

OIL VAPOUR FAN (TURBINE)

ON OR READY TO OPERATE

+

OIL VAPOUR FAN (GENERATOR)

ON OR READY TO OPERATE

+

-

SUBL. CONTR. OIL VAPOUR FAN GEN ¶

ONE OUT OF TWO VAPOUR FANS

¶

OF THE TURBINE OIL TANK AND

¶

THE GENERATOR MUST BE IN

¶

OPERATION AS LONG AS THE

¶

GENRATOR IS FILLED WITH

¶

HYDROGEN

ONE OILCOOLER OILSIDE ¶

CHECK OILCOOLER(S) IN SERVICE

¶

AT THE INDICATOR AT THE

¶

CHANGE-OVER VALVE (S).

¶

DO NOT ADJUST ANY INTERMEDIATE

¶

POSITION OF CHANGE-OVER VALVE

COOLING-WATER F. OIL - COOLER(S) ¶

OPERATION OF THE COOLING

¶

WATER-SYSTEM ACCORDING TO

¶

SEPARATE INSTRUCTION NOT

¶

INCLUDED IN THE TURBINE

¶

MANUAL

© PMI, NTPC

IN SERVICE

AVAILABLE

172

-

SERVICE OILCOOLER (WATERSIDE)

FILLED AND VENTED

-

COOLING - WATER PIPE

VENTED

-

STAND-BY OIL-COOLER WATERSIDE

DRAINED

AND

DRIED

-

-

-

¶

IF THE OILCOOLER IN STAND-

¶

BY CANNOT BE DRIED BY OIL

¶

FLOWING VIA THE FILLING

¶

AND THE VENT -LINE, THE

¶

OIL COOLER IN STAND- BY

¶

MUST BE EXPOSEDTO THE

¶

FULL FLOW OF COOLING WATER

¶

ONCE WEEKLYTO PREVENT

¶

DEPOSITS CAUSING

¶

CORROSIVE ATTACKS

¶

T0 THE MATERIAL.

OIL LEVEL IN TANK ¶

COMPARE ACTUAL VALUES WITH

¶

TEST REPORT VALUES DURING

¶

STAND STILL OF OIL-PUMPS.

OIL FILTERS INCL. STAND BY ¶

FILTER- INSERTS CLEANED

¶

OR

¶

FILTER REPLACED

OIL PROPERTIES ¶

OIL CLEAR

¶

NO COLLECTION OF WATER AT

¶

THL BOTTOM OF THE OIL TANK

------------------------------------------------------------

© PMI, NTPC

NORMAL

READY TO OPERATE

NORMAL

-----------------------------------

173

(02)

+

GENERATOR READY F. OPERATION

CHECK

+

MANUAL OPERATED VALVES GENERATOR

ADJUSTED

+

GENERATOR HYDROGEN

FILLED

+

HYDROGEN PURITY

> 94 %

+

SEAL OIL PUMP AIRSIDE

ON

+

STAND-BY SEAL OIL PUMP AIRSIDE

OFF

+

SEAL OIL PUMP GASSIDE

ON

+

(03)

¶

THE DC-SEAL-OIL PUMP WILL

¶

ONLY BE OPERATED IF THE

¶

AC- POWER SUPPLY IS FAULTY.

SUBLOOP CONTROL OFF SEAL-OIL- PPS ¶

THE SEAL OIL PLANT MUST ALSO

¶

BE IN OPERATION IF THE

¶

TURNING GEAR WILL BE OPERATED

¶

EVEN THE GENERATOR IS NOT

¶

FILLED WITH HYDROGEN.

ON

+

SEAL-OIL PLANT

NO ALARM

+

LIQUID IN GENERATOR

NO ALARM

------------------------------------------------------------

-----------------------------------

CRITERIA FOR BEGIN OF START-UP

CHECK

+

¶

IF THE FOLLOWING CRITERIA

¶

ARE FULFILLED THE SYSTEM

¶

WILL BE STARTED- UP FROM

© PMI, NTPC

174

¶ +

(STANDSTILL).

AUXILIARY OIL PUMP

OFF AND

+

+

BEARING OIL PUMP ¶

THE BEARING OIL-PUMP WILL

¶

ONLY BE OPERATED IF THE

¶

AUXILIARY OILPUMPS FAIL

¶

F.E. IF THE AC-POWER SUPPLY

¶

IF FAULTY.

TURNING GEAR OIL VALVE

OFF

CLOSED

AND +

SUBLOOP CONTROL TURNING GEAR

OFF

+

SUBLOOP CONTR. OF AUX. OILPUMPS AND

OFF

+

SUBLOOP CONTR. OF BEAR-OILPUMP

OFF

+

SHAFT LIFT OIL PUMP

OFF

AND +

SUBL. CONTROL. OF SHAFT LIFT

OFF

OIL-PP

(04)

+

------------------------------------------------------------

-----------------------------------

FGA (OILSYSTEM)

START

¶

OPERATION PUSH BUTTONS

¶

GF A = FUNCTIONAL GROUP

¶

AUTOMATIC

OR

© PMI, NTPC

175

+

(05)

+

(05/S) *+ +

OILSYSTEM MANUAL OPERATED

START

------------------------------------------------------------

-----------------------------------

AUXILIARY OIL PUMP

SWITCH ON

AUXILIARY OIL PUMP

ON

OR WITH FGA (OIL SUPPLY)

ON

AUXILIARY OILPUMP 1

ON

OR AUXILIARY OIL PUMP 1

FAULTED

AUXILIARY OIL PUMP 2 MANUAL

ON

OPERATE

(06)

2

+

OIL PRESSRE

> 5KG/CM

+

LUBE OIL PRESSURE

> 1, 2KG/CM2

+

OIL LEVEL IN TANK

NO ALARM

+

FILTER-SUPERVISORY THRUST BEARING

NO ALARM

¶

DIFF-PRESSURE ACROSS FILTER

NOT HIGH

¶

PRESSURE BEHIND FILTER

NOT LOW

¶

LOCAL INDICATOR

NOT INITIATED

¶

CHECK STAND-BY-FILTER BY

¶

LOCAL CHANGE-OVER

+

TURNING GEAR OIL VALVE

OPEN

+

TURNING GEAR OIL VALVE

OPEN

OR WITH SUBLOOP CONTROL +

SUBLOOP CONTROL TURNING GEAR

SWITCH ON

+

SUBLOOP CONTROL TURNING GEAR

ON

© PMI, NTPC

176

OR WITH FGA (OIL SUPPLY) (06/S) *+

SUBLOOP CONTROL TURNING GEAR

ON

¶

SUBLOOP-CONTROL OPENS AND

¶

CLOSES THE TURNING GEAR OIL-

¶

VALVES DEPENDING ON TURBINE/

¶

GENERATOR SPEED.

¶

TURNING GEAR VALVE (OPEN)

> 210 RPM

¶

TURNING GEAR VALVE (CLOSED)

> 240 RPM

¶

TURNING GEAR OIL VALVE

¶

CLOSED DURING START- UP AND

¶

OPENS WHEN THE TURBINE IS

¶

COASTING-DOWN AFTER. SHUT -

¶

DOWN.

¶

DO NOT SWITCH OFF SUBLOO

¶

CONTROL AS LONG AS TURBINE

¶

+*

(07)

+ +

¶

IS IN OPERATION TO MAKE SURE

¶

TURNING GEAR CUTS IN IF

¶

TURBINE WILL BE SHUT -DOWN.

TURNING GEAR OIL VALVE

OPEN

OIL LEVEL IN TANK

NO ALARM

SUBLOOP CONTR. OF AUX. OILPUMPS AND

SWITCH ON

SUBLOOP CONTR. OF BEAR-OILPUMP

SWITCH ON

+

SUBLOOP CONTR. OF AUX. OILPUMPS AND

ON

+

SUBLOOP CONTR. OF BEAR-OILPUMP

ON

OR WITH FGA (OIL SUPPLY)

© PMI, NTPC

177

(07/S) *+ *+

(08)

SUBLOOP CONTR. OF AUX. OILPUMPS AND

ON

SUBLOOP CONTR. OB BEAR-OILPUMP

ON

¶

THE SUBLOOP CONTROLS START

¶

THE AUXILIARY OIL PUMPS AND

¶

THE DC-BEARING OIL PUMPS

¶

DE PENDING ON PRESSURE

¶

AUXILIARY OIL PUMP 1

< 4,8KG/CM2

¶

AUXILIARY OIL PUMP 2

< 4,6KG/CM

¶

AUXILIARY OIL PUMP 24 V

< 1,3KG/CM

¶

DC-BEARING OIL PUMP 220 V

< 1,2KG/CM

¶

SIMULTANEOUSLY ALARMS WILL

¶

BE ACTUATED

¶

LUBRICATING OIL PRESSURE

¶

AND/OR

¶

LUBRICATING OIL

¶

THE SUBLOOP CONTROLS MUST

¶

NOT BE SWITCHED-OFF UNTIL

¶

THE SHAFT WILL BE STOPPED

¶

COMPLETELY.

2

2

+

SEAL-OIL PRESSURE GENERATOR

CHECK

+

SEAL-OIL PRESSURE AIRSIDE TE

> P MIN

+

SEAL-OIL PRESSURE AIRSIDE EE

> P MIN

+

SEAL-OIL PRESSURE GASSIDE TE

> P MIN

+

SEAL-OIL PRESSURE GASSIDE EE

> P MIN

=

SUBLOOP CONTROL OF SEAL-OIL-PPS

ON

¶

THE SUBLOOP-CONTROL OF THE

¶

SEAL-OIL PUMPS START THE

¶

PUMPS DEPENDING ON SEAL-

¶

OIL PRESSURE.

© PMI, NTPC

2

178

(09)

¶

P MIN ACCORDING TO ACTUAL

¶

H2 -PRESSURE.

-------------------------------------------------------------------

-----------------------------------

+

SHAFT LIFT OIL PUMP

SWITCH ON

+

SHAFT LIFT OIL PUMP

ON

OR WITH SUBLOOP CONTROL +

SUBL. CONTR. OF SHAFT LIFT OIL-PP

SWITCH ON

+

SUBL. CONTR. OF SHAFT LIFT OIL-PP

ON

+

OR WITH FGA (OIL SUPPLY)

(09/S*+) *+

+

SUBL. CONTR. OF SHAFT LIFT OIL-PP

ON

SHAFT LIFT OIL PUMP

ON

OR SHAFT LIFT OIL PUMP

FAULTED

SHAFT LIFT LIFT OIL PUMP MANUAL OPER

ON

¶

SUBLOOP CONTROL STARTS AND

¶

STOPS THE SHAFT LIFT-OIL

¶

PUMP 1 DEPENDING ON TURBINE/

¶

GENERATOR SPEED-CRITERIA.

¶

SHAFT-LIFT-OIL-PUMP 1 (ON)

< 510 RPM

¶

SHAFT-LIFT-OIL-PUMP 1 ( OFF)

> 540 RPM

¶

SUBLOOP CONTROL STARTS THE

¶

SHAFT-LIFT-OIL-PUMP 2

¶

DEPENDING ON SHAFT-LIFT-OIL-

¶

PRESSURE

¶

SHAFT LIFT OIL PUMP (ON)

¶

SUBLOOP CONTROL STARTS THE

© PMI, NTPC

< 100 KG/CM2

179

¶

SHAFT-LIFT-OIL-PUMPS 2

¶

AND 3 DEPENDING ON SHAFT-

¶

LIFT-OIL-PRESSURE.

¶

SHAFT-LIFT-OIL-PUMP 2 (ON)

< 100 KG/CM

¶

SHAFT-LIFT-OIL-PUMP 3 (ON)

< 100 KG/CM2

¶

SHAFT-LIFT-OIL-PUMP 3 MUST

¶

ONLY BE OPERATED IF SHAFT

¶

TO OPERATE F. E. DUE TO LACK

¶

OF AC- POWER-SUPPLY.

¶

DO NOT SWITCH OFF SUBLOOP

¶

CONTROL OF SHAFT-LIFT-OIL-

¶

PUMP TO MAKE SURE SHAFT-

¶

LIFT-OIL-PUMP STARTS DURING

¶

COASTING-DOWN AFTER SHUT DOWN

¶

OF THE TURBINE

¶

NOTE!

¶

DO NOT STOP SHAFT-LIFT-OIL-

¶

PUMP DURING TURNING GEAR

¶

OPERATING UNLESS THE SHAFT

¶

HAS COME TO A COMPLETE STAND-

¶

STILL AFTER CLOSING THE

¶

TURNING GEAR OIL- VALVE

¶

INTENTIONALLY.

2

TEMPERATURE CRITERIA The ission steam temperatures should meet the metal temperatures as shown below in order to start and load the turbine in shortest possible time. Note:

The criteria above represent approximate values, which can be optimized by operational experience. Turbines with Functional Group Automatic (FGA) for the start-up must under go optimizing. The values obtained are given in the operational data record. Criteria for the opening of stop valves

© PMI, NTPC

180

When opening the main stop-valves the main steam parameters should meet the following recommended values. Steam with 50°C superheat -

Minimum Main Steam Temperature

MS

>

S + 50°C

MS

=

Main Steam at Steam generator Outlet

S

=

Temperature of saturated steam (depending on main steam pressure)

and MS

>

(MCV 50%)

MS

=

Main Steam temperature at Steam generator outlet

MS 50% =

Middle wall temperature of main control valve casing.

MS

>

(MCV 50%)

MS

=

Main Steam temperature at Steam generator outlet

MCV 50% =

Middle wall temperature of main control valve

-

Maximum main steam pressure ahead of the turbine

Pmax.

=

(MCV 50%)

Pmax.

=

Maximum main steam pressure ahead of the turbine.

MCV 50%

=

Middle wall temperature of main control valve.

© PMI, NTPC

181

If the control valve temperatures MCV 50% exceed the temperature of the saturated steam belonging to the main steam pressure the pressure criteria must not be observed.

STARTING CRITERIA When the main control valves are opened the main steam and reheat temperatures should fulfill the following criteria: -

Minimum main steam-temperature

MS

>

S + 50°C

MS

=

Main Steam temperature ahead of the turbine

S

=

Temperature of aturated steam (depending on main Steam Pressure)

MS

>

(HT 50%)

MS

=

Main Steam temperature ahead of the turbine

HT 50% =

Middle wall temperature of HP-Casing or simulated middle phase Shaft temperature.

-

Minimum reheat temperature.

Reh

>

(IT 50%)

Reh

=

Steam temperature in the hot reheat line

IT 50% =

© PMI, NTPC

Simulated middle phase temperature of the IP-shaft.

182

SPEEDING UP CRITERIA Before the turbine is brought to rated speed the main Steam temperature MS ahead of the turbine should fulfil the following criteria: MS

>

(HT 50%)

MS

=

Main Steam temperature ahead of the turbine

HT 50% =

Middle wall temperature of HP-Casing or simulated middle phase Shaft temperature.

LOADING CRITERIA Before the turbine is loaded the reheat temperature ahead of the turbine should fulfil the following criteria: Reh

>

(IT 50%)

Reh

=

Steam temperature in the hot reheat line

IT 50% =

© PMI, NTPC

Simulated middle phase temperature of the IP- turbine shaft.

183

WARMING UP AND STARTING UP THE TURBINE CONTROLLERS

1.

Operating modes of the control systems and of the starting and load limit device Electrical speed control

The turbine generator unit is accelerated

- Warm-up operation

and maintained at constant warm-up speed

- Running up the turbine/ generator unit

accelerate unit to rated speed maintain unit

high speed governor

at rated speed

Hydraulic governor

The turbine generator unit is accelerated

- Warm-up operation

and maintained at constant warm-up speed by manual actuation of the starting and load limit device.

- Running up the turbine generator unit

When the reference speed setter is in the 0% position, the hydraulic governor takes over speed control at approx. 80% rated speed. So, run-up of the turbine generator unit from approx. 80 to 100% rated speed is

controlled

by

the

hydraulic

speed

governor. - Rated speed operation

Maintain unit at rated speed acceleration to

- Overspeed trip test

107% of rated speed by the governor; speed is increased to trip speed using acceleration lever on casing of hydraulic governor; During overspeed trip test, the electrical speed controller must be disengaged and switched off.

© PMI, NTPC

184

Starting and load limit device - Setting operating con figuration of main trip valves

The main trip valves are brought into operating position when the starting and load limit device is in the 0% position.

- Opening the stop valves

When the starting and load limit device is in approx 40% open position, the stop valves should be open; the test valves must be in the operating position for the opening procedure.

- Warm-up operation

2.

see Hydraulic speed governor.

Electrical Speed Control Control range in % rated speed

0-107% (limitation by hydra ulic speed

Setpoint control

governor)

- Target setpoint/actual setpoint

The actual setpoint follows the target setpoint along preset gradients.

- Limitation of setpoint by turbine stress evaluator (TSE)

The preset gradient is reduced according to

a

predetermined

characteristic

to

conform to the margin generated by the TSE. - Application of the TSE signal

The TSE signal must always be present if the TSE is not faulted.

- Operation with TSE

The actual setpoint no longer follows the target setpoint if the TSE is faulted; the actual

and

target

setpoints

must be

matched up before the TSE signal can be switched off. When the signal from the TSE is not present, the thermal stresses in the

© PMI, NTPC

185

turbine components must be figured out by comparing the actual temperatures and their

differences

with

the

curves

for

permissible temperature margins. Limitation by higher - level or alternative controllers or other devices - Minimum value selection

Effective controller = controller with the lowest setpoint setting at any time (also applies to other devices influencing the opening characteristic)

- Hydraulic speed governor (speed setting device approx. 80%)

- Starting and load limit device

Limits setpoint by hydraulic minimum value selection;

Limits setpoint by hydraulic minimum value selection; excessive control valve opening can be prevented by using the starting and load limit device to limit valve travel.

Operation

see arrangement of control desk release

- Operating elements and monitoring push button. instruments - Operating logic sequences for changing the operating mode

3.

See Appendix (for changing the operating mode during no-load operation).

Hydraulic Speed Governor Setpoint control - Target setpoint/actual setpoint

The actual setpoint immediately follows the target set-point (no influence from turbine

© PMI, NTPC

186

stress evaluator). During operation with the hydraulic speed governor, the thermal stresses in the turbine components must be figured out on the basis of the TSE display or, if the TSE is faulted, by comparing the actual temperatures and their

difference

with

the

curves

for

permissible temperature margins. Limitation by higher - level or alternative controllers or other devices - Minimum value selection

Effective controller = controller with lower set-point setting at any time (Also applies to other devices influencing the control characteristic)

- Electro - hydraulic controller < 100%

Limits setpoint by hydraulic minimum value selection

- Starting and load limit device

Limits setpoint by hydraulic minimum value selection.

© PMI, NTPC

187

OPERATION +

Turbine generator unit

=

Turning gear speed

speed +

Stop valve position

=

0%

+

Control valve position

=

0%

+

Main trip valves

=

depressurized

+

Starting and load limit

=

40% open

+

Reference speed setter

=

0%

+

Electrical speed

=

0%

reference (1)

(2)

(3)

(4)

(A)

+

Electrical speed reference

=

raise

+

Electrical speed reference

=

0%

+

Plunger coil

deenergise

+

Plunger coil

deenergised

+

Starting and load limit device

+

Starting and load limit device

=

+

Main trip valves

in operating configuration

+

Starting and load limit device

Raise

+

Starting and load limit Device

>40%

+

Stop valve position

=

+

Warm-up criteria for main steam lines

Fulfilled

+

Main Steam Lines

Warm-up

+

Criteria for ission

fulfilled

+

Steam generation

adequate

© PMI, NTPC

lower 0%

100%

188

(5)

+

Starting and load limit device

Raise

+

Control valve

Open

+

Turbine Generator

=

Warm-up speed

Unit (6)

+

Using starting and load limit device

maintain constant speed

(B)

+

Turbine

Warm-up

+

Run-up criteria

=

fulfilled

+

Steam generator output

=

adequate

+

Starting and load limit Device

+

Control valve

=

Open

+

Turbine Generator

>

Warm-up speed

=

75% Rated speed

(7)

Raise

Unit Speed +

Turbine Generator Unit Speed

(8)

+

Starting and load limit Device

+

Starting and load limit

Raise =

100% Open

Device (9)

+

Reference Speed Setter

+

Turbine generator unit Speed

Operating logic sequence

Raise =

Rated speed

1:

Starting up the turbine generator unit with the starting and load limit device and the hydraulic speed governor

© PMI, NTPC

189

Warming up the Main Steam Line B see Warming up and Starting up the Turbine. +

(1)

(2)

(3)

Turbine generator unit speed

>

turning gear speed and 75% rated

<

speed

+

Electrical speed reference

=

turbine generator unit speed

+

Reference speed setter

=

100%

+

Starting and load limit

=

56 to 100%

+

Starting and load limit device

Lower

+

Starting and load limit device

effective

+

Electrical speed reference

Raise

+

Electrical speed reference

+

Plunger Coil

deenergise

+

Plunger Coil

deenergised

(4)

Using starting and load limit device

(5)

+

Reference speed setter

+

Reference speed setter

Operating Logic Sequence

=

100 %

maintain constant speed Lower =

0%

2:

Transition from operating with electrical

speed controller to

operation, with starting and Toad limit

device (Speed approx. 80%

rated speed)

© PMI, NTPC

190

+

Turbine generator unit speed

>

Turning gear speed and 75% rated speed

(1)

(2)

(3)

(4)

+

Electrical speed reference

<

100%

+

Plunger coil

=

deenergised

+

Reference speed setter

=

0%

+

Starting and load limit

=

effective

+

Plunger Coil

energise

+

Plunger Coil

energised

+

Electrical speed reference

lower

+

Turbine Generator Unit

+

Starting and load limit device

raise

+

Starting and load limit device

56 to 100%

+

Reference speed setter

raise

+

Reference speed setter

100%

Operating logic sequence

=

3:

electrical speed reference

Transition from operation with starting and load limit device to operation with electrical speed controller (Speed approx. 80% rated speed).

© PMI, NTPC

191

SYNCHRONIZATION AND LOADING (01)

+

GENERATOR READY TO BE SYNCHRONIZED

CHECK

+

SPEED OF TURBINE/

3000 RPM

GENERATOR

(02)

+

DRAIN OF SEAL STEAM HEADER

NORMAL

+

H2 -SUPPLY SYSTEM

NO ALARM

+

SEAL-OIL PLANT

NO ALARM

+

PRIMARY WATER SYSTEM

NO ALARM

+

LIQUID IN GENERATOR

NO ALARM

+

STEAM TEMPERATURE CRITERIA

FULFILLED

------------------------------------------------

----------------

+

EXITATION BREAKER

SWITCH ON

+

EXITATION BREAKER

SWITCHED ON

OR WITH FGA (TURBINE CONTROL) +

(03)

EXITATION BREAKER

SWITCHED ON

------------------------------------------------

----------------

+

GENERATOR VOLTAGE

SET HIGHER

+

GENERATOR VOLTAGE

HIGHER

OR WITH FGA (TURBINE CONTROL)

© PMI, NTPC

192

+

(04)

AUTOMATIC SYNCHRONIZER

ON

------------------------------------------------

----------------

+

GENERATOR VOLTAGE CONTROL

CLOSED

+

GENERATOR VOLTAGE CONTROL

SWITCHED ON

OR WITH (AUTOMATIC SYNCHRONIZER) (04/S)*+

(05)

+

GENERATOR VOLTAGE CONTROL

SWITCHED ON

------------------------------------------------

----------------

SYNCHRONOCOPE

SWITCHED ON

OR WITH (AUTOMATIC SYNCHRONIZER) +

(06)

+

+

SYNCHRONOCOPE

SWITCHED ON

------------------------------------------------------------

-----------------------------------

GENERATOR VOLTAGE

ADJUSTED

¶

BY MEANS OF REFERENCE

¶

VALUE OF VOLTAGE CONTROL

GENERATOR / LINE-VOLTAGE

MET

OR WITH (AUTOMATIC SYNCHRONIZER) (07/S)*+

(08)

+

+

GENERATOR / LINE-VOLTAGE

MET

------------------------------------------------------------

-----------------------------------

GENERATOR FREQUENCY

ADJUSTED

¶

BY MEANS OF REFERENCE

¶

VALUE OF SPEED CONTROL

GENERATOR / LINE- FREQUENCY

© PMI, NTPC

MET

193

OR WITH (AUTOMATIC SYNCHRONIZER) (08/S)*+

(09)

GENERATOR / LINE-FREQUENCY ¶

GENERATOR FREQUENCY

¶

MUST BE ADJUSTED IN SUCH A WAY

¶

THAT THE NEEDLE OF THE

¶

SYNCHRONOSCOPE TURNS

¶

SLOWLY IN THE DIRECTION

¶

GENERATOR FREQUENCY HIGHER

¶

THAN LINE FREQUENCY=

¶

FAST SYNCHRONIZING.

¶

FAST SYNCHRONIZING ENSURES

¶

THAT THE GENERATOR WILL

¶

BE LOADED IMMEDIATELY

¶

AFTER SYNCHRONISING THUS

¶

PREVENTING REVERSE POWER

¶

RELAY TO BE ACTUATED.

MET

------------------------------------------------------------

-----------------------------------

+

SYNCHRONIZING DEVICE

START

+

GENERATOR BREAKER

SWITCHED ON

¶

IF THE BREAKER WILL BE

¶

SWITCHED ON MANUALLY

¶

ADJUST PHASE ANGLE TO

¶

NEEDLE OF SYNCHRONOSCOPE

¶

MUST MEET THE ZERO-ANGLE

¶

MARK ON THE SCALE WHEN

¶

SWITCHING IN BREAKER.

OR WITH (AUTOMATIC SYNCHRONIZER) +

GENERATOR BREAKER

SWITCHED ON

------------------------------------------------------------

-----------------------------------

© PMI, NTPC

194

(10)

(11)

+

SPEED REFERENCE VALUE

SET HIGHER

+

GENERATOR LOAD

> 10%

------------------------------------------------------------

-----------------------------------

+

STARTING AND LOAD LIMIT DEVICE

SET HIGHER

+

STARTING AND LOAD LIMIT DEVICE

100%

OR WITH FGA (TURBINE CONTROL) +

(12)

STARTING AND LOAD LIMIT DEVICE

100%

------------------------------------------------------------

-----------------------------------

+

TURBINE STRESS EVALUATOR (TSE)

CHECK

+

TURBINE STRESS EVALUATOR (TSE)

CHANGED OVER

¶

AT A PRESET MINIMUM LOAD

¶

THE USE CHANGES OVER FROM

¶

TEMPERATURE-TO LOAD SCALE

------------------------------------------------------------

-----------------------------------

+

GENERATOR LOAD

>10%

+

LOAD CONTROLLER

SWITCHED ON

¶

THE LOAD CONTROL WILL BE

¶

SWITCHED ON AT A PRESET

¶

MINIMUM LOAD.

+

LOAD REFERENCE VALUE

SET HIGHER

+

LOAD REFERENCE VALUE

TARGET LOAD

------------------------------------------------------------

-----------------------------------

© PMI, NTPC

195

(13)

+

(13/S) *+

(14)

+

WAIT LIMITED LOAD REFERENCE VALUE ¶

THE LIMITED LOAD REFERENCE

¶

VALUE FOLLOWS THE TARGET LOAD

¶

REFERENCE VALUE WITH THE

¶

ADUSTED LOAD GRADIENT.

¶

THE LOAD GRADIENT WILL BE

¶

REDUCED, IF REDUCTION OF THE

¶

TSE-ALLOWANCE OCCUR.

¶

THE TSE INFLUENCE WILL BE

¶

EFFECTIVE VIA THE REFERENCE

¶

LIMITER.

¶

IF THE TSE FAULTED THE

¶

DIFFERENTIAL TEMPERTURES

¶

AT THE MEASURING POINTS

¶

WHICH REPRESENT THE ADDI-

¶

TIONAL THERMAL STRESSES

¶

OF CASING AND ROTOR MUST BE

¶

EVALUATED.

DRAIN DOWNSTREAM RCV

HIGHER

CLOSE

OR WITH SUBLOOP CONTROL (DRAINS)

+

+

POSITION OF DRAINS

CHECK

DRAIN DOWNSTREAM OF HP-CONTR. VLV

CLOSED

¶

CRITERIUM:

¶

VALVE CASING TEMPERATURE

¶

MINUS SATURATION TEMPERATURE

¶

OF STEAM

DRAIN OUTER CASING

© PMI, NTPC

> 50 CEL

CLOSED

196

+

+

(15)

(1)

¶

CRITERIUM:

¶

TEMP. HP-CASING TOP

DRAIN AHEAD OF SWING-CHECK CRH ¶

CRITERIUM:

¶

NON RET. CHECK VLV COLD REH.

> 320 CEL CLOSED OPEN

DRAIN UPSTREAM RCV

CLOSED

¶

CRITERIUM:

AND

¶

VALVE CASING TEMPERATURE

> 50 CEL

¶

MINUS SATURATION TEMPERATURE

¶

OF STEAM

------------------------------------------------------------

-----------------------------------

+

HEATER OPERTION

CHECK

+

HEATERS

IN OPERATION

+

EXTRACTION VALVE

> 0%

+

DRAINS OF ETRACTIONS

CLOSED

¶

IF THE EXTRACTION STEAM

¶

FLOW WILL BE REDUCED,

¶

CAUSING THE EXTRACTION

¶

VALVE TO CLOSE THE

¶

RESPECTIVE DRAIN MUST

¶

BE OPEN

------------------------------------------------------------

-----------------------------------

+

BOILER/TURBINE LOAD RELATION

1

+

BY CONTROL VALVE

CHECK

+

BY CONTROL VALVE

CLOSED AND

+

BY STOP VALVE

CLOSED AND

© PMI, NTPC

197