12 Regulation Of Alternator By Emf Method 1q4k5r

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Circuit Diagram: (a) OC & SC Test

(b) Armature Resistance

Name Plate Details: Parameter Power Voltage Current Speed type Excitation Voltage Excitation Current P.F.

DC Motor

Alternator

REGULATION OF ALTERNATOR USING SYNCHRONOUS IMPEDANCE METHOD

Exp. No. 12 Date:

AIM: To pre-determine the regulation of a given three-phase alternator by conducting O. C. and S. C. tests by synchronous Impedance method (EMF method) Apparatus Required: S.No.

Equipment

1.

Tachometer

Range 0-

Type

Quantity

DIGITAL

1

10,000RPM (0-2A)

MC

1

2.

Ammeter

(0-20A)

MC

1

3.

Voltmeter

(0-300V)

MC

1

(0-50V)

MC

1

1-Ph

1

T.W.W

2

4.

Rectifier

5.

Rheostat

230/0-270V 300/2A

PROCEDURE: 1.

OC test: (i)

Connections are made as shown in the circuit diagram for OC & SC test.

(ii)

With the rectifier in the zero voltage position, TPST switch open and the rheostats in their proper positions, the d.c. supply to the motor is switched ON.

(iii)

The dc motor is brought to rated speed of the alternator by properly varying the field rheostat of motor.

(iv)

Now, the alternator field is excited by applying the dc voltage through the rectifier in steps. At each step, note down the field current and the corresponding generated voltage. This procedure is repeated till the voltage generated is much beyond rated value.

(v)

Reduce the alternator field excitation to zero level.

MODEL GRAPHS

Tabulation: a) OC & SC Test:

O. C. Test

S. C. Test

Speed = S.No.

xxxx

Field current

Phase voltage

(A)

(V)

Speed = S.No.

Field

Short circuit

current,

current (ISC), (A)

(If) (A)

2.

SC test (i)

with the rectifier in the minimum voltage position, the TPST switch is closed.

(ii)

Increase field excitation gradually till the S.C. current of the alternator reaches the rated current of alternator.

(iii)

Note down all the meter readings.

b) Armature Resistance: S.No.

I (A)

V (volts)

Rdc

=

V/I

Ω

Percentage regulation at _______ load at different power factors Power factor (Cosφ )

E0 (V) Lagging

Leading

% Reg Lagging

Leading

Model Calculations: From Graph Z S =

VOC for the same If and speed: = I SC

Ra = (1.6) RdC = XS =

Z S2 − Ra2

=

Assume p.f. (CosΦ) = Assume armature current (Ia) = Generated emf of alternator on no load is

E0 =

( v cos φ + I a

Ra )

2

+ ( v sin φ ± I a X S )

2

=

+ for lagging p.f. - for leading p.f. The percentage regulation of alternator for a given p.f. is

% Re g =

E 0 −V x 100 = V

where E0 – Generated emf of alternator per phase voltage V – Full load, rated terminal voltage per phase.

Result:

Comments: