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Circuit Diagram:

(a) OC & SC Test

(b) Armature Resistance

Name Plate Details:

Parameter DC Motor Alternator

Power

Voltage

Current

Speed

type

Excitation Voltage

Excitation Current

P.F.

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

.

Equipmen

t

Range Type Quantity

1. Tachometer 0-

10,000RPM

DIGITAL 1

2. Ammeter

(0-2A) MC 1

(0-20A) MC 1

3. Voltmeter (0-300V) MC 1

(0-50V) MC 1

4. Rectifier 230/0-270V 1-Ph 1

5. Rheostat 300/2A T.W.W 2

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 = xxxx Speed =

S.No

.

Field current

(A)

Phase voltage

(V)

S.No. Field

current,

(If) (A)

Short circuit

current (ISC), (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

Percentage regulation at _______ load at different power factors

Power

factor

(Cos)

E0 (V) % Reg

Laggin

g

Leadin

g

Laggin

g

Leadin

g

Model Calculations:

From Graph for the same If and speed: =

Ra = (1.6) RdC =

=

Assume p.f. (CosΦ) =

Assume armature current (Ia) =

Generated emf of alternator on no load is

=

+ for lagging p.f.

- for leading p.f.

The percentage regulation of alternator for a given p.f. is

=

where

E0 – Generated emf of alternator per phase voltage

V – Full load, rated terminal voltage per phase.

Result:

Comments: