Page 48 - Practical Power System and Protective Relays Commissioning

44 Practical Power System and Protective Relays Commissioning

characteristic field current shown on the X axis and the rated voltage
on the Y axis.
6. Short circuit characteristic test. Run the generator at the rated speed in
the short circuit of generator stator terminals then record the generator
short circuited current at 25%, 50%, 75%, 100% of excitation voltage
and current. Create a graph with the short circuit characteristic field cur-
rent on the X axis and rated current on the Y axis.
7. Phase sequence test with respect to direction of rotation. Measure the
phase sequence in the rotation direction of anticlockwise.
8. Voltage balance test. The three-phase voltages are checked for balance
when generator runs in the rated voltage and rated speed but in an open
circuit condition.
9. Vibration test. Run the generator in the rated voltage and rated speed;
the vibration is measured at the vertical, horizontal, and axial direction
on the bearings.
10. Impedance test of rotor. One-phase variable voltage is applied to rotor
field winding and current is measured. Record the reading at 25%, 50%,
75%, and 100% of the rated field voltage.
11. Momentary overload test. The generator is run at the rated speed with
stator terminals short-circuited, then generator is excited to 150% of its
field current for 30 seconds.
12. Noise level test. With the machine running at the rated speed, a voltage
measurement on no-load and noise is taken at different locations of the
machine, distance 1 m, using a noise level meter. Then the machine is
switched off and ambient noise is measured. Using these two numbers,
the machine noise is calculated.
13. Over speed test. The machine is run at 120% of the rated speed for
2 minutes. No disturbance should be noticed during that time.
14. Wave form measurement test. The machine is run at the rated speed
and rated voltage; the three-phase voltages are recorded using a
suitable instrument.
15. Trial tests.
16. On load tests.
17. Tests of the cooling system.
18. Testing of the lubrication system.

4.8 SYNCHRONOUS MOTORS THEORY

Synchronous motors consist of stator and rotor windings that are placed on
the stator and the rotor respectively as shown in Fig. 4.11.
The stator winding supplied with a three-phase supply generates a rotat-
ing field in the stator. The two rotating fields in the stator and the fixed field
on the rotor are linked and cause the rotor to rotate in a synchronous speed
by a torque generated by the two electric fields.