Page 45 - Practical Power System and Protective Relays Commissioning

Generators and Motors: Theory and Testing Chapter | 4 41

4.4.4 Power Angle of Synchronous Machines
The angle δ between the generator emf voltage vector (E) and generator ter-
minal voltage vector (V) is called a power angle, or a load angle. When the
load of a synchronous machine changes, the load angle oscillates about mean
position and this condition is called machine hunting. To overcome this con-
dition, a synchronous generator is equipped with a damper winding on the
rotor which produces a damping torque.

4.4.5 Excitation Response

The excitation response is the rate of change in exciter voltage and defined
by volts per seconds-slope of voltage time curve at a certain load condition.

4.4.6 Excitation Ceiling Voltage
The maximum voltage that may be given by an exciter at certain load condi-
tion is called the excitation ceiling voltage.

4.5 GENERATOR CONNECTION IN POWER STATIONS

As shown in Fig. 4.10 the main items in this scheme of connection are the
generator, unit auxiliary transformer, station service transformer, high volt-
age switchgear and switchgear for transformers with low voltage.

4.6 SYNCHRONIZING OF SYNCHRONOUS GENERATOR
WITH BUSBARS
The process of paralleling a synchronous generator with an infinite busbar of
a networks with a voltage, phase sequence, and frequency is called generator
synchronizing.
Conditions of synchronizing are:

1. The voltage of the generator should be equal to the voltage of the busbar.
2. Phase sequences should be the same for the generator and the busbar.
3. The frequency should be the same for the generator and the busbar
The steps of synchronizing are as follows:
1. Run the synchronous generator in synchronous speed.
2. Increase the excitation current to increase the terminal voltage gradually
to the nominal voltage value of generator.
3. Ensure the generator and busbars are at the same voltage and frequency.
4. Check that the phase sequence indicator is anticlockwise.
5. Increase the frequency of the generator to 0.1 cycle more than the busbar
frequency.