TP-6079 3/00 19Section 5 Generator Troubleshooting
10. Set the engine speed to 47.5 Hz for 50 Hz
generator sets and 57.5 Hz for 60 Hz generator
sets for the desired cut-in frequency.
11. Slowly turn the volts/Hz pot counterclockwise until
the frequency matches that of the engine
frequency (47.5 or 57.5 Hz) or until the voltage just
begins to drop.
12. Reset the engine speed to the normal frequency
(50Hzor60Hz).
13. Recheck the AC voltage output and stability as
described in steps 4--7.
14. Stop the generator set.
5.3 Rotor
The two-pole rotor creates the magnetic field needed to
sustain alternating current in the stator windings. Before
testing, inspect the rotor for visible damage to pole
shoes, insulation, exposed coil windings, and collector
ring surfaces. Check the rotor bearing for noisy
operation, excessive wear, radial or axial movement,
and/or heat discoloration. Replace the rotor as
necessary.
Collector rings acquire a glossy brown finish in normal
operation. Do not attempt to maintain a bright, newly
machined appearance. Wipe the collector rings with a
dry, lint-free cloth. Use a commutator stone to remove
the groves on the collector rings. Do not use emery or
carborundum paper or cloth. Remove all carbon dust
from the generator. Remove the black or pitted surface
of the collector rings using a lathe.
Check the rotor for continuity and resistance. Lift the
brushes and measure the rotor resistance between the
two collector rings. See Section 5.5.
Note: When checking rotor resistance with the rotor
installed, brushes must not be in contact with
rotor collector rings. Use a brush retainer on
brushes for accurate resistance readings.
Note: Use the values in Section 1 as a reference for
rotor resistance readings. Take readings at room
temperature or about 21°C(70°F). Rotor
resistance will vary directly with increase in
temperature.
To check whether the rotor is shorted to ground, touch
one ohmmeter lead to either collector ring and the other
lead to the rotor poles or shaft. The meter should
register no continuity.
Repair or replace the rotor if the previous tests detect
any faults.
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