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Experiment No. 3

Synchronous Generator Parameters

Objectives

The objectives of this experiment are to find the synchronous reactance (Xd) and mutual

reactance from open circuit characteristic and reactive loading of a 3- φ synchronous generator.

Apparatus

1. 2 test tables

2. DC motor-synchronous generator set

3. 1 Ω field rheostat

4. 1 5 A Kenwood DC power supply

5. 1 0-5 A DC ammeter

6. 1 0-10 A DC ammeter

7. 1 0-150 V DC voltmeter

8. 1 current transformer

9. 1 0-5 A AC ammeter

10. 2 Wattmeters

11. 1 0-300/150 V AC voltmeter

12. Tachometer for synchronous generator

13. Strobe

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Procedure

Part 1: Open Circuit Characteristic (OCC)

a) Set up the circuit shown in Fig.1. The synchronous generator should be connected for

220 V 3- φ wye operation. b) Start the DC motor.

c) Adjust IFmotor until the speed of the dc motor-synchronous generator set, n, is at

synchronous speed; i.e., n = ns. d) Holding the speed constant, adjust IFgen until VOC equals 140% of rated voltage.

Measure and record IFgen, VOC and n.

e) Turn off the motor-generator set.

Part 2: Reactive Loading of Synchronous Generator

a) Set up the circuit shown in Fig.2. The synchronous generator should be connected for

220 V 3- φ wye operation. b) Keep the switches of test table 2 open. Start the DC motor.

c) Adjust IFmotor until the speed of the dc motor-synchronous generator set, n, is at

synchronous speed; i.e., n = ns. d) Adjust IFgen until the voltage across the terminals of synchronous generator is brought

to rated value. Measure IFgen.

e) Make sure that the capacitive bank is connected to the rated voltage. Initially, set the

capacitive bank to infinity.

f) Close the switches of test table 2 and adjust the load to 20A approximately. Measure

the currents (I1, I2, and I3) and voltages (V12, V23, and V31) at the terminals of the

source.

g) Repeat part f for different load conditions. Make sure the load is balanced.

h) Turn off the motor-generator set.

Report

1. Plot the open circuit characteristic VOC versus IFgen. Draw a tangent passing through

the origin to the graph. Find the slope of the tangent and this will give you direct axis

mutual inductance Xmd.

Xmd1

n

i

2

3VOC

i⋅

Ifi

∑=

n

2. From part 2 of the experiment, for the measured value of IFgen, find VOC from OCC.

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3. Find Xd using equation

VT Ean Ias ra⋅− j Iad⋅ Xd⋅− jIaq Xq⋅−

Where Ean is the induced emf

VT is the measured terminal voltage of the synchronous machine

Xd is the direct axis reactance

Xq is the quadrature axis reactance

Ias is the stator line current in phase A.

Iad is the direct axis stator current

Iaq is the quadrature axis stator current.

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Tabular Form for Open Circuit Characteristic (OCC):

S.No IFgen

A V12

V

V23

V

V31

V VOC

V12 V23+ V31+

3 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

Tabular Form for Reactive Loading:

S.No I1

A

I2 A

I3 A

IL A

V12

V

V23

V

V31

V

VT

V

IFgen A

VFgen V

IFmotor

A

NS

RPM

1.

2.

3.

4.

5.

6.

7.

8.

9.

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Where

ILoad

I1 I2+ I3+

3

VT

V12 V23+ V31+

3 3⋅

NS = Synchronous speed

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120 VDC

L1

A

F

L2

TEST TABLE 1

DC MOTOR

AC GENERATOR

120 VDC

TEST TABLE 2

IFgen

VOC

Fig. 1: Circuit diagram of the laboratory setup for determining the open circuit characteristics

120 VDC

L1

A

F

L2

TEST TABLE 1

DC MOTOR

AC GENERATOR

120 VDC

TEST TABLE 2

IFgen

VOC

IHR1

Inductive

Load

Fig. 2: Circuit diagram of the laboratory setup for reactive loading.