Page 47 - Practical Power System and Protective Relays Commissioning

Generators and Motors: Theory and Testing Chapter | 4 43

4. Installation of cooling system of generator to be carried out correctly as
per the approved detailed design by the utility engineers.
5. Checking of insulation of generator stator, and supply and control and
protection cables by a Megger DC test.
6. Tests on generator stator and other equipment with generator.
7. Drying out of generator: heating up the insulation to reduce the
absorbed moisture then repeat the Megger insulation test.
8. Trial run test, no-load run under supervision of the unit and its
auxiliaries.
9. Setting and testing of protective relays as per the approved relay setting
table and relay testing procedures.
10. Final commissioning and hand over to the customer.

4.7.1 The Pre-start Commissioning Tests of Synchronous
Generators

The following prestart commissioning tests should be undertaken:
1. Measurement of the winding resistance of the main stator, exciter stator,
and exciter rotor using a micro-Ohm meter.
2. Measurement of insulation resistance of winding. This test is done
before and after the high voltage test on the main stator, main rotor,
exciter stator, and exciter rotor. A Megger 1000 V is used for stator
winding for 1 minute. The Polarization Index Test is used to calculate
the ratio of insulation resistance for 10 minutes through to insulation
resistance for 1 minute.
3. High voltage tests at power frequency on main stator. This test is done
on site for generator stator winding under a voltage following this
equation:
V test 5 (2 V 1 1) kV between phase and ground with the other two
phases connected to the ground for 1 m for each phase. The test voltage
is raised quickly to the maximum test voltage. It is kept at that value
for 1 minute and then reduced slowly to zero.
4. High voltage tests of the power frequency on the main rotor, exciter sta-
tor, and rotor. This test is done on site under a voltage following this
equation:
V test 5 (10 3 field voltage/nominal voltage) Volts not less than
1500 voltage AC between phase and ground with the other two phases
are connected to the ground for 1 minute for each phase.
5. Open circuit characteristic test. The generator is run at a rated speed
in an open circuit gradually increase the excitation voltage to have
20%, 40%, 60%, 80%, 90%, 95%, 100%, 105%, 110%, and 120% of
rated voltage. Record the generator voltage, excitation voltage, and
excitation current then create a graph with the open circuit