220 Kv Substation Report 1w4b4

1. INTRODUCTION 220 KV GRID is located in Devigarh, Patiala .The grid receives 220 KV lines and steps down further into 66 KV and 11 KV lines .The 66KV Grid was setup in the year 1973 and it is modified to 220KV up to Feb 2014The various components used for stepping down the voltage and protection are installed in the grid like transformers , circuit breakers, relays , current transformers ,potential transformers ,battery bank, busbar, lightning arrestor , insulators ,capacitor banks and various other sensors and devices.

Incoming Feeder:

220KV Bhateri(Bhadurgarh)

Outgoing Feeder:

66 KV

1. Bhunerheri 2. Magar Sahib 3. Rohar Jagir 

11 K.V.

1. Jhawalapur

10. S.S.Wala

2. Mehon

11. Dudhan

3. Bangra

12. UPS-01

4. Kisanpur

13. UPS-02

5. Partapgarh

14. UPS-03

6. Hasanpur

15. Binjal

7. Masingan

16. Julkhan

8. Shekhupur

17. Gagrola

9. Bhunerheri

18. Waliyan

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NEED OF PROJECT WORK The project entitled “STUDY OF VARIOUS COMPONENTS USED IN 220 KV DEVIGARH GRID AND PROTECTION ,MAITENANCE OF POWER TRANSFORMER” was carried out to have deep and sound knowledge of what are the various components used in the grid , how are the various components installed , what is the use of the various components , how do these components work etc . It also gave a knowledge of how the power transformer operate, its protection, maintenance and lot of other things related to transformer. This project made me aware of all these things. Our main purpose for this visit is to be familiar with industrial environment and to get practical knowledge of electrical power transmission and distribution Students of 3rd semester will get the idea of electrical power transmission and distribution.

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2. SUBSTATION An electrical sub-station is an assemblage of electrical components including busbars, switchgear, power transformers, auxiliaries etc. These components are connected in a definite sequence such that a circuit can be switched off during normal operation by manual command and also automatically during abnormal conditions such as short-circuit. Basically an electrical substation consists of No. of incoming circuits and outgoing circuits connected to a common Bus-bar systems. A substation receives electrical power from generating station via incoming transmission lines and delivers elect. power via the outgoing transmission lines. Sub-station are integral parts of a power system and form important links between the generating station, transmission systems, distribution systems and the load points.

Fig 2.1 Graphical view of 220 KV Grid MAIN TASKS Associated with major sub-stations in the transmission and distribution system include the following: 1.

Protection of transmission system.

2.

Controlling the Exchange of Energy. 3

3.

Ensure steady State & Transient stability.

4.

Load shedding and prevention of loss of synchronism. Maintaining the system frequency within targeted limits.

5.

Voltage Control; reducing the reactive power flow by compensation of reactive power, tap-changing.

6.

Securing the supply by proving adequate line capacity.

7.

Data transmission via power line carrier for the purpose of network monitoring; control and protection.

8.

Fault analysis and pin-pointing the cause and subsequent improvement in that area of field.

9.

Determining the energy transfer through transmission lines.

10.

Reliable supply by feeding the network at various points.

11.

Establishment of economic load distribution and several associated functions.

TYPES OF SUBSTATION

The substations can be classified in several ways including the following : 1.

Classification based on voltage levels, e.g. : A.C. Substation : EHV, HV, MV, LV; HVDC Substation.

2.

Classification based on Outdoor or Indoor : Outdor substation is under open skv. Indoor substation is inside a building.

3.

4.

Classification based on configuration, e.g. : 

Conventional air insulated outdoor substation or



SF6 Gas Insulated Substation (GIS)



Composite substations having combination of the above two

Classification based on application 

Step Up Substation : Associated with generating station as the generating voltage is low.



Primary Grid Substation : Created at suitable load centre along Primary transmission lines.



Secondary Substation : Along Secondary Transmission Line.



Distribution Substation : Created where the transmission line voltage is Step Down to supply voltage. 4

Bulk supply and industrial substation : Similar to distribution sub-station but



created separately for each consumer. Mining Substation : Needs special design consideration because of extra



precaution for safety needed in the operation of electric supply. Mobile Substation Temporary requirement. NOTE : 

Primary Substations receive power from EHV lines at 400KV, 220KV, 132KV and transform the voltage to 66KV, 33KV or 22KV (22KV is uncommon) to suit the local requirements in respect of both load and distance of ultimate consumers. These are also referred to ‘EHV’ Substations.



Secondary Substations receive power at 66/33KV which is stepped down usually to 11KV.



Distribution Substations receive power at 11KV, 6.6 KV and step down to a volt suitable for LV distribution purposes, normally at 415 volts.

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3. LIGHTNING ARRESTOR Lighting arrestor is a device, which protects the overhead lines and other electrical apparatus viz , transformer from overhead voltages and lighting When the positively charged cloud produce negative charge on the overhead line by electrostatic induction then the negative charge is however presented right under the cloud and portion of the line away from the cloud becomes positively charged This charge on the line does not flow Every instrument must be protected from the damage of lighting stroke. The three protection sin a substation is essential:

Protection for transmission line from direct strokes



Protections of power station or substation from direct strokes



Protection of electrical apparatus against traveling waves

Effective protection of equipment against direct strokes requires a shield to prevent lighting from striking the electrical conductor together with adequate drainage facilities over insulated structure. Installation Location :Install arrester electrically as close as possible to the appearatus being protected Line and ground connections should be short and direct

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Fig 3.1 Lightning Arresters Grounding:The arrester ground should be connected to the apparatus grounds and the main station ground utilizing a reliable common ground network of low resistance. The efficient operation of the lightning arrester requires permanent low resistance grounds : Station class arresters should be provided with a ground of a value not exceeding five ohms. Clearances:- These are given on the drawings. These are the maximum recommended. The term ‘clearance’ means the actual distance between any part of the arrester or disconnecting device at line potential, and any object at ground potential or other phase potential. It consist of a isolator in series and connected in such a way that long isolator is in upward and short isolator is in downward so that initially large potential up to earth is decreased to zero An ideal arrestor must therefore have the following properties: 1. It should be able to drain the surge energy from the line in a minimum time 2. Should offer high resistance to the flow of power current 3. Performance of the arresters should be such that no system disturbances are introduced by its operation 4. Should be always in perfect from to perform the function assigned to it

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5. After allowing the surge to , it should close up so as not to permit power current to flow to ground

Fig 3.2 Lightning Arresters Working:Lightning, is a form of visible discharge of electricity between rain clouds or between a rain cloud and the earth The electric discharge is seen in the form of a brilliant arc, sometimes several kilometres long, stretching between the discharge points How thunderclouds become charged is not fully understood, but most thunderclouds are negatively charged at the base and positively charged at the top However formed, the negative charge at the base of the cloud induces a positive charge on the earth beneath it, which acts as the second plate of a huge capacitor When the electrical potential between two clouds or between a cloud and the earth reaches a sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes 8

ionized along a narrow path and a lightning flash results.

4. WAVE TRAP It is used to trap the communication signals & send PLCC room through CVT. Rejection filters are known as the line traps consisting of a parallel resonant circuit ( L and C in parallel) tuned to the carrier frequency are connected in series at each and of the protected line such a circuit offer high impedance to the flow of carrier frequency current thus preventing the dissipation. The carrier current used for PLC Communication have to be prevented from entering the power equipments such as attenuation or even complete loss of communication signals. For this purpose wave trap or line trap are used between transmission line and power station equipment to avoid carrier power dissipation in the power plant reduce 9

cross talks with other PLC Circuits connected to the same power station. Ensure proper operating conditions and signal levels at the PLC transmit receive equipment irrespective of switching conditions of the power circuit and equipments in the stations. Line matching filter and protective equipment:For matching the transmitter and receiver unit to coupling capacitor and power line matching filters are provided. These flitters normally have air corral transformers with capacitor assumed. The matching transformer is insulated for 7-10 KV between the two windings and perform two functions. Firstly, it isolates the communication equipment from the power line. Secondly, it serves to match . Transmitter:The transmitter consists of an oscillator and a amplifier. The oscillator generates a frequency signal with in 50 to 500 HZ frequency bands the transmitter is provided so that it modulates the carrier with protective signal. The modulation process usually involves taking one half cycle of 50 HZ signal and using this to create block to carrier.

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Fig 4.1 Wave Trap

Receivers:The receivers usually consist of and alternate matching transformer band filter and amplifier detector. The amplifier detector converts a small incoming signal in to a signal capable of operating a relatively intensive carrier receiver relay. The transmitter and receiver at the two ends of protected each corresponds to local as far as transmitting.

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5. ISOLATOR When carrying out inspection or maintains work in substation ,it is essential to disconnect reliability the unit of other station on which the work is done from all other parts on installation in order to ensure full safety of working staff .So guard against mistake it is desirable that should be done by an apparatus is called “ISOLATOR”. In other words a device which is used to open or close the circuit either when negligible current is interrupted or when no significant change in voltage across the terminal of each pole of the isolator will result from operation .they must only be opened or closed when current is zero. There is single ear thing Isolator used . Isolator is switching device used to open (or close) a circuit either when a negligible current exists or when no significant change in voltage across the terminal of each pole of the isolator, will result from the operation. Broadly speaking isolator are the switches which’s operate under "No current” condition.

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Fig 5.1 View of Isolator

Isolators are file with earthing blades as an integral part of it. They may be isolators with single ear thing blades or two earthling blades on either side of it.They must only be opened or closed when current is zero. Isolators are classified into following categories. 1.

Bus isolator

2.

Line isolator 13

3.

Transformer isolating switch From constructional point of view the isolator may be classified as1.The post- centre post rotating part, double post break type. 2.Two post single type. 3.Base: - Each pipe phase isolator is mounted on a robust base of steal construction.

6. POTENTIAL TRANSFORMER There are two types of instrument transformer:1. Potential Transformer 2. Current Transformer

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Potential Transformer:Similar to CT it is another type of instrument type of instrument transformer .Transformer used for voltage measurements are called voltage transformer or Potential transformer. it may be of 1 phase or 3 phase These transformers make the instruments suitable for measurement of high voltage and isolating then from high voltage. these TX. Are connected in parallel and secondary winding is always open ckt. The primary has large no of turn in secondary,which provided step down of voltage , and then the voltmeter is connected across secondary terminal the high voltage line.Some related to PT :-

1. Rated voltage :- the capacity voltage of the PT which it can stand 2. Rated transformer ratio:- The ratio of the rated primary voltage to the rated second voltage. 3. Rated secondary voltage:- 130 / root (3) = 63.3 VAR. Voltage transformer which step down system voltage to sufficient form high value to low value are necessary in every system for Induction of d.c supply voltage conduction. Metering of the supply of energy. Relaying Syncronizing. Design and ranges are selected according to the secondary size of potential transformer for indicating instruments, meter and relays. But calibration of these instruments is done according to the primary voltage

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Fig 6.1 Potential Transformer

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7. CURRENT TRANSFORMER

The current transformers are kept in the category of the instrument transformer. The C.T. are used to reduce/ stepping down A.C form high value to lower value for measurement / protection / control. They are usually installed in the outdoor switch. The primary conductor at high voltage with respect to earth. The secondary of C.T. is just like the ring type C.T. the primary winding consists of a very few turns , and therefore there is no. appreciation volt drop across injection Current is transformed by C.T. the current transformer is used with primary winding , connected in series with the line carrying the current to be measured and therefore primary current is dependent upon load connected in the system.

Fig 7.1 Current Transformer

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Measurement of alternating current is one of the most frequent operation not only because of it’s inheriant but a also because it is necessary in determining other parameters of electrical circuit. A current transformer value of current is used for 1. Indication of current 2. kwh and kw meters 3. Telementry 4. Protective relay etc A current transformer is intended to operate normally with rated current of the system flowing through the primary winding which is increased in the series with the network Secondary winding of current transformer connected to measuring instruments and relay supplies currents circulating in the design of current transformer.

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8. POWER TRANSFORMER

There are two power transformers of 160 MVA and 100 MVA . They are used convert 220 KV/66KV.And two power transformers are used of 20 MVA and 16/20 MVA which convert 66KV/11KV. Which transforms e/e energy from one voltage level to another desired level with corresponding change in current value and without any change in frequency value. The physical basis of a transformer is mutual induction between the circuits linked by a common magnitude pulse voltage supplied to one set of winding called primary switch builds up a magnitude flux through the iron. A transformer in simplest form consist of two magnetic coil, which are electrically separated from each other but magnetically linked through path of reluctance .

Fig 8.1 Power Transformer

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Transformer parts are:1. BUCHHOLZ RELAY: It is a very sensitive gas and oil operated instrument which safely detect the formation of gas or sudden pressure inside the oil transformer. 2. CONSERVATOR: It is used to provide adequate space for the expansion of oil when transformer is loaded or when ambient temprature changes. 3. SILICA GEL BREATHER: It sucks the moisture from the air which is taken by transformer so that dry air is taken by transformer. 4. DOUBLE DIAPHRAGM EXPLOSION VENT: It is used to discharge excess pressure in the atmosphere when excess pressure is developed inside the transformer during loading. 5. OIL LEVEL INDICATOR: It is used to show the oil level in the transformer. 6. Winding temperature indicator: used to show the temperature of transformer winding. 7. RADIATORS: These are used for cooling of the transformer oil.

Fig 8.2 Various Parts of Transformer

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9. INSULATOR

Transmission line insulators are devices used to contain, separate or electrical conductors on high voltage electricity supply networks. Transmission insulators come in various shapes and types, including individual or strings of disks, line posts or long rods. They are made of polymers, glass and porcelain--each with different densities, tensile strengths and performing properties in adverse conditions. Pin Type Insulators Pin type insulators are used for the transmission of lower voltages. A single pin type insulator is used to transmit voltages up to 11 kV (kilovolts) and higher voltages require two-, three- or four-piece pin insulators. They are not economically feasible for 33 kV and higher transmission lines. Pin type insulators are secured with steel or lead bolts onto transmission poles. These are typically used for straight-running transmission lines.

Fig 9.1 Pin type insulator Suspension Type Insulators:Suspension type transmission line insulators suspend and high voltage transmission lines. They are cost effective for higher voltage transmission, typically replacing multiple pin type insulators. Suspension type insulators have a number of interconnected porcelain discs, with each individual unit designed to a particular voltage. Together, a system of these 21

discs is capable of effectively ing high voltages. There are three types of suspension insulators: cemented cap suspension insulators; interlinking or Hewlett suspension insulators; and link or core suspension insulators.

Fig 9.2 Suspension type insulator Strain Type Insulators Strain type insulators are horizontally suspended suspension insulators. They are used to handle mechanical stresses and take the pressure off a conductor at the end of a transmission line, at a sharp corner or curve or over long river crossings. Strain insulators are typically used for higher voltage transmissions.

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Fig 9.3 Strain type insulator Shackle Type Insulators:Shackle type insulators, similar to strain type insulators, are used on sharp curves, end poles and in section poles. However, unlike strain insulators, shackle insulators are designed to lower voltages. These insulators are single, round porcelain parts that are mounted horizontally or vertically.

Fig 9.4 Shackle type insulator

10. CIRCUIT BREAKER A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. In any circuit, carrying a large amount of current, if a is opened then normally a spark is produced due to fact that current traverses its path through air gap Arcing is harmful as it can damage precious equipment media are provided between s. This is one of the important equipment in power system It protects the system by isolating the faulty section while the healthy one is keep on working Every system is susceptible to 23

fault or damages while can be caused due to overloading, short-circuiting, earth fault etc thus to protect the system and isolate the faulty section C B are required Apart from breaking and making s, a C B should be capable of doing 1. Continuously carry the maximum current at point of installation 2. Make and break the circuit under abnormal and normal condition Close or open the faulty section only where fault exists There are different arc quenching media:1)

Air blast

2)

Oil

3)

SF6 gas

4)

Vacuum In 220 kV Grid Devigarh , SF6 gas circuit breaker are used, as for greater capacity SF6 type breakers are very efficient . SF6 BREAKER The outstanding physical and chemical properties of SF6 gas makes it an ideal dielectric media for use in power switchgear.These properties of SF6 gas makes it an ideal dielectric media for use in power switchgear,these properties are included: 1) High dielectric strength 2) unique arc quenching ability 3) Excellent thermal stability 4) Good thermal conductivity In addition, at normal temperature SF6 is chemically inert,inflammable,noncorrosive and non-condensable at low temperatures. SF6 versus oil :SF6 is not flammable and toxic like oil.It is easier to handle,maintain and repair equipment filled with SF6. In case of breakdown of oil strong surges of pressure may occur due to sudden development of gaseous products.In case of breakdown of SF6,the only pressure rise will result from the thermal expansion of gas.

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Fig 10.1 SF6 Circuit Breaker

11. EARTHING Earthing is the provision of a surface under the substation, which has a uniform potential as nearly as zero or equal to Absolute Earth potential. The provision of an earthing system for an electric system is necessary by the following reason. 1. In the event of over voltage on the system due to lighting discharge or other system fault. These parts of equipment which are normally dead as for as voltage, are concerned do not attain dangerously high potential. 2. In a three phase, circuit the neutral of the system is earthed in order to stabilize the potential of circuit with respect to earth. The resistance of earthing system is depending on shape and material of earth electrode used. the earthing is of two principal types :-

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1. Neutral Earthing 2. Equipment Body Earthing Neutral Earthing:Neutral Earthing also known as System Neutral Earthing (or Grounding) means connecting the neutral point i.e. the star point of generator,transformer etc. to earth. In rotating machines, generator, transformer circuit etc., the neutral point is always connected to earth either directly or through a reactance. The neutral point is usually available at every voltage level from generator or transformer neutral. If neutral point is not available, then the most common method used is using a Zigzag transformer. Such a transformer has no secondary. Each phase of primary has two equal parts. There are 3 limbs and each limb has two winding, providing flux density under normal condition. Since the fluxes are opposite, the transformer takes very small magnetizing current under normal conditions. During fault, the circuit is primary side, which provides very less impedance to the current. The grounding transformers are short time rating. Their size is almost one tenth as compared to power transformer. Electrical Earthing:electrical Earthing is different from neutral earthing. During fault condition, the metallic parts of an electrical installation which do not carry current under normal conditions, may attain high potential with respect to ground. As human body can tolerate only I=0.165A/T current for a given time t so to ensure safety we connect such metallic parts to earth by means of Earthing system ,which comprises of electrical conductor to send fault current to earth. The conductor used is generally in the form of rods, plates, pipes etc. Earthing system ensures safety in following ways :1. The potential of earthen body does not reach dangerously high value about earth, since it is connected to earth. 2.

Earth fault current flows through earthing and readily causes the operation of fuse or an earth relay.

Connection of Electrical Equipment to Substation:S.No. Apparatus ing of bus 1. insulator

Path to be connected Base plate 26

2. 3. 4. 5.

High voltage circuit

Operating mechanism frame

breaker Isolator Potential transformer Power transformer

Operating mechanism frame bed Transformer tank LV Core tank

Merits of neutral Earthing:1. Arcing grounding is reduced. 2. Voltage of heating with respect to earth remains at harmless value they don't increase to root 3 times of normal value. 3. Suitable neutral point. 4. The earth fault relaying is relatively simple useful amount of earth fault current is available to operate earth fault relay. 5. The over voltage due to lightening are discharged to earth. 6. Improved service reliability due to limitation of arcing ground and improved of unnecessary fringing of CB. At Devigarh the neutral point of power transformer is connected solidly to earth generally the earth connection are provided which leads reliability.

12. PROTECTION RELAY A relay is an electrically operated switch Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch s The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches. Relays allow one circuit to switch a second circuit which can be completely separate from the first For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical. The coil of a relay es a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to

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the larger value required for the relay coil The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification Types of Relays These are called normally opened, normally closed in GSS control room there is in which the relays are set and there are many types of relays 1. Over voltage relays 2. Over current relays 3. I D M T fault relay 4. Earth fault relay 5. Bucheloz’s relay 6. Differential relay OVER VOLTAGE RELAY: - This protection is required to avoid damage of system in case line becomes open circuited at one end These fault would trip the local circuit breaker thus block the local and remote ends This relay is operated i e , energized by CVT connected to lines. OVER CURRENT RELAY: -This relay has the upper electromagnet of non-directional relay connected in series with lower non-directional electromagnet When the fault current flow through relay current coil which produces flux in lower magnet of directional element Thus the directional relay has the winding over the electromagnets of non-directional element and produces a flux in lower magnet and thus over current operates. EARTH FAULT RELAY: -when a conductor breaks due to some reason and it is earthen then earth fault occurs The fault current is very high thus, there is need to of over current relay This relay has minimum operating time DIRECTIONAL RELAY: - It allows flowing the current only in one direction then only this relay operates It has a winding connected through the voltage coil of relay to lower magnet

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winding called current coil Which is energized by C T if fault occurs This relay operates when v/I is less than theoretical value The v/I is normally constant .

Fig 12.1 Over Current and Voltage Relays DIFFERENTIAL RELAY: - This relay operates when phase difference of two electrical quantities exceeds the predetermined value It has always two electrical quantities; hence in 400kv GSS for transformer differential relay is used INVERSE TIME CHARACTERISTICS RELAY: - The relay using here having the inverse time characteristics having the time delays dependent upon current value This characteristic is being available in relay of special design There are:i.

Electromagnetic Induction type

ii.

Permanent magnetic moving coil type

iii.

Static type

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BUCHHOLZ’S RELAY: - It is the protective device of the transformer When any fault occurs in the transformer then it indicates about fault and we disconnect the transformer from the circuit It is used in the power transformer It is connected between the tank and conservator It has two floats on which two mercury switch are attached One float is used for the bell indication and other float is used for the tripping In the normal position the relay is filled with the oil and s of the mercury switch are opened When the earth fault occurs in the transformer then it increases the temperature of oil and oil flows into the conservator through relay On the way it makes the s of the tripping circuit short So in the we can say that this relay works as circuit breaker.

Fig12.2 Buchholz Relay

13. CONTROL ROOM

To remote control of power switch gear requires the provision of suitable control plates located at a suitable point remote from immediate vicinity of CB 's and other equipments. 30

At "220KV DEVIGARH" the separate control room provided for remote protection of 220KV switch yards transformer incoming feeder, outing feeders. Bus bar has their own control plant in their control rooms. The control carrier the appropriate relays. Necessary meters indicating lamp control switches and fuses. There are meters for reading purpose. A circuit concerning the is shown on the with standard co lour. On each a control switch is provided for remote operation of circuit breaker. There are two indicators which show that weather circuit breaker is closed or open. A control switch for each insulator is also provided. The position indicator of isolator is also done with the help of single lamp and indicator. The co lour of signal lamps are as follows :RED :- For circuit breaker or isolator is close option GREEN :- For CB or isolator in open position.

In addition to used indication an alarm is also providing for indicating abnormal condition when any protective relay or tripping relay has operated. Its constants energies on auxiliary alarm. Relay which on operation completes the alarm belt circuit. Energy Meter:These are fitted on different to record transmitted energy and recorded in energy hours. For this purpose MWH meter have been provided. Watt Meter:This is mounted on each feeder to record import or export power. Frequency Power:Provided to each feeder to measure frequency which analog or digital. Volt Meter :Provided on each or the purpose of indication of voltage. Ammeter:31

These are used to indication the line current. MVAR Meter:Provided for indicating power factor of import and export. Maximum Indicator Demand :Chief requirement of these indicators to record the minimum power factor taken by feeder during a particular period. This record the average power successive predetermined period.

Fig 13.1 Control Room

14. BATTERY ROOM

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There is a battery room which has 55 batteries of 2 volt each for 132KV section and 110 batteries for 220KV section. Therefore D.C. power available is for functioning of the control s. A battery charger to charge the battery. 1. Various parts of lead acid batteries:1. Plates 2. Separators 3. Electrolyte 4. Container 5. Terminal port 6. Vent plugs

Fig 14.1 View of Battery Room

CHARGING OF BATTERIES:-

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Initial charging It is the first charging given to batteries by which the positive plates are converted to “lead peroxide”, whereas the –ve plates will converted to spongy lead. Also in a fully charged battery the electrolyte specific gravity will be at its highest venue or 1.2 and its terminal voltage will be 24 volts Discharging:When a fully charged battery delivers its energy out by meeting a load the lead peroxide of the +ve plates slowly gets converted to lead sulphate and the spongy lead of the –ve plates also gets converted into lead sulphate during this time the specific gravity of the electrolyte also decreases the value around 1.00 and the terminal voltage also decreases from its initial to a lower value which may be around 1.85 or 1.8.

15. CAPACITOR BANK

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A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in series with one another. These groups of capacitors are typically used to correct or counteract undesirable characteristics, such as power factor lag or phase shifts inherent in alternating current (AC) electrical power supplies. Capacitor banks may also be used in direct current (DC) power supplies to increase stored energy and improve the ripple current capacity of the power supply. Single capacitors are electrical or electronic components which store electrical energy. Capacitors consist of two conductors that are separated by an insulating material or dielectric. When an electrical current is ed through the conductor pair, a static electric field develops in the dielectric which represents the stored energy. Unlike batteries, this stored energy is not maintained indefinitely, as the dielectric allows for a certain amount of current leakage which results in the gradual dissipation of the stored energy. The energy storing characteristic of capacitors is known as capacitance and is expressed or measured by the unit farads. This is usually a known, fixed value for each individual capacitor which allows for considerable flexibility in a wide range of uses such as restricting DC current while allowing AC current to , output smoothing in DC power supplies, and in the construction of resonant circuits used in radio tuning. These characteristics also allow capacitors to be used in a group or capacitor bank to absorb and correct AC power supply faults.

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Fig 15.1 Capicator Bank The use of a capacitor bank to correct AC power supply anomalies is typically found in heavy industrial environments that feature working loads made up of electric motors and transformers. This type of working load is problematic from a power supply perspective as electric motors and transformers represent inductive loads, which cause a phenomenon known as phase shift or power factor lag in the power supply. The presence of this undesirable phenomenon can cause serious losses in of overall system efficiency with an associated increase in the cost of supplying the power. The use of a capacitor bank in the power supply system effectively cancels out or counteracts these phase shift issues, making the power supply far more efficient and cost effective. The installation of a capacitor bank is also one of the cheapest methods of correcting power lag problems and maintaining a power factor capacitor bank is simple and cost effective. One thing that should always be kept in mind when working with any capacitor or capacitor bank is the fact that the stored energy, if 36

incorrectly discharged, can cause serious burns or electric shocks. The incorrect handling or disposal of capacitors may also lead to explosions, so care should always be exercised when dealing with capacitors of any sort.

CONCLUSION The training at grid substation was very helpful. It has improved my theoretical concepts of electrical power transmission and distribution. Protection of various apparatus was a great thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc was observable. I had a chance to see the remote control of the equipments from control room itself, which was very interesting. So the training was more than hope to me and helped me to understand about power system more. Now I have studied a lot about the electrical transmission system. One must have never thought that so many things are required for just switching on a television or a refrigerator or say an electric trimmer. The three wing of electrical system viz. Generation, transmission and distribution are connected to each other and that too very perfectly. Here man and electricity work as if they are a family. Lots of labour, capital and infrastructure is involved in the system just to have a single phase,220V,50Hz power supply at our houses. At last I would say...

Energy Saved Is Energy Produced

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REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.

www.electrical4u.com www.wikipedia.com www.youtube.com www.slideshare.com “Power System” by C.L.Wadhwa “Power System” by V.K. Mehta “Electrical Machine” by P.S. Bimbra Thapar Library

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