Page 779 - Basic Electrical Engineering

Figure 10.12 Phasor diagram of a synchronous generator at lagging power factor load

For leading power factor load, it will be seen that

To calculate voltage regulation we have to calculate E using the above
relation. While V, ϕ, R , I will be known, the value of synchronous reactance
a
a
has to be determined. The vector sum of armature resistance and synchronous
reactance will give the value of synchronous impedance.

10.13 DETERMINATION OF VOLTAGE REGULATION BY THE SYNCHRONOUS
IMPEDANCE METHOD

The direct method of determining voltage regulation is to load the generator
and measure its full-load terminal voltage. Then remove the load and measure

its no-load voltage, without changing the excitation. Then, calculate voltage

regulation using the relation, Volt regulation =

However, for large machines, it may not be possible to find such loads in
the testing laboratory. Further, there will be huge power loss due to loading

during the testing time. For these reasons an indirect method of testing is
always used.