Page 251 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

SYNCHRONOUS GENERATORS

12.14 CHAPTER TWELVE

V remains constant. Therefore, the armature reaction voltage jX I has increased while

S A
keeping the same angle. Since
E V jX I
A
S A

jX I must increase while the magnitude of E remains constant (Fig. 12.18a). Therefore,
S A A
when the load increases, the voltage V decreases sharply.

Figure 12.18b illustrates the effect when the generator is loaded with a unity power
factor. It can be seen that V decreases slightly. Figure 12.18c illustrates the effect when

the generator is loaded with leading power factor loads. It can be seen that V increases.

The voltage regulation is a convenient way to compare the behavior of two generators.
The generator voltage regulation (VR) is given by
VR
100%
V nl V fl
V fl
where V and V are the no-load and full-load voltages, respectively, of the generator.
nl fl
When a synchronous generator is operating at a lagging power factor, it has a large positive
voltage regulation. When a synchronous generator is operating at a unity power factor, it has
a small positive voltage regulation, and a synchronous generator operating at a leading
power factor has a negative voltage regulation.

FIGURE 12.18 The effect of an increase in generator loads at constant power factor upon its terminal volt-
age: (a) Lagging power factor; (b) unity power factor; (c) leading power factor.

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