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sevensecond time delay.
c.
If the load contactor does not open under the conditions described in step (b), refer to the
Troubleshooting Chart in Section 2-4.
d.
If the under voltage circuit performs satisfactorily, return unit to normal operation by adjusting
output voltage coarse adjustment potentiometer for normal output voltage, pressing the reset
push button switch, and closing the load contactor.
(7)
Check under frequency sensing circuit, protective monitor, and indicating light. At some
frequency value from 380 Hz or less, after 7 seconds, the under frequency condition should
signal the under frequency circuit in the protective monitor module to OPEN the load contactor
holding circuit, thus OPENING the load contactor. To check the under frequency protective
components, proceed as follows:
a.
While the unit is operating normally under load, reduce generator output frequency by
reducing engine speed. Use the governed speed setting potentiometer (Fig. 5). Turn
adjusting screw gradually COUNTERCLOCKWISE to reduce engine speed until frequency
meter indicates 385 Hz. Under frequency protective circuit should not open the load
contactor at this frequency.
b.
Reduce frequency in steps of 1 Hz, with a time delay of 7 seconds between steps.
c.
If the protective circuit opens the load contactor and turns on the under frequency light after 7
seconds at 380 Hz, all components of the system are functioning properly.
d.
If the load contactor is not opened at 380 Hz after 7 seconds, refer to Troubleshooting Chart
to determine which component is defective.
e.
Return unit to normal operating condition.
(8)
Check over frequency sensing circuit, protective monitor, and indicating light.
At some frequency value from 420 Hz to 480 Hz, after 7 seconds, the over frequency sensing
circuit should signal the over frequency circuit in the protective monitor module to OPEN the load
contactor holding circuit, thus OPENING the load contactor.
At any frequency value exceeding 480-Hz, the over frequency sensing circuit should immediately
signal the over frequency circuit in the protective monitor module to OPEN the load contactor
holding circuit, thus OPENING the load contactor.
To check the over frequency protective components, proceed as follows:
a.
While the unit is operating normally under load, increase generator output frequency by
increasing engine speed. Use the governed speed setting potentiometer (Ref. Fig. 5). Turn
adjusting screw CLOCKWISE gradually to increase engine speed until frequency meter
indicates 415 Hz. Over frequency protective circuit should not open the load contactor at this
frequency.
b.
Increase frequency in steps of 1 Hz, with a time delay of 5 seconds between steps.
c.
If the protective system opens the load contactor and turns on the over frequency light after 5
seconds at 426 Hz, all components of the system are functioning properly.
d.
If the load contactor is not opened at 426 Hz after 5 seconds, refer to Troubleshooting Chart
to determine which component is defective.
e.
Return unit to normal operating condition.
(9)
If the generator is operating under load at this point, place the contactor control switch(s) (22 and
24, Fig. 1) in OFF position to open load contactors and disconnect load. There will be no further
need for the load bank in the following check.
OM-2084 / Operation and Maintenance Manual
90CU24 / Series 500392 Generator Sets
Chapter 2-3
November 27/1997
Page 8
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