Hobart 9OC24S Operation Manual page 170

GENERATOR DIVISION
HOBART BROTHERS COMPANY
OPERAT'ION , MAINTENANCE, AND OVERHAUL MANUAL, TM-240A
SELF-PROPELLED GENERATOR SET, SPEC. NO. 5381A
NOTE: It may be necessary to switch to MANUAL control to obtain
these low voltages.
(c)
If the load contactor is not opened at 103 V to 93 V, it will be necessary
to refer to the Trouble Shooting Chart, 3-2, Figure 6, to determine which
component of the undervoltage protective circuit is defective.
(d) If the undervoltage circuit performs satisfactorily, return the unit to normal
operation by adjusting the voltage to 115 V, pressing the reset switch, and
closing the load contactor.
(40)
Ch ec un er requency sensing relay, protective monitor, and indicating light. k d f
At some frequency value (Hz, cycles-per-second) from 385 Hz down to 375 Hz,
the underfrequency sensing relay should function to signal the underfrequency
circuit in the protective monitor module to OPEN the load contactor holding
circuit, thus OPENING the load contactor. To check the underfrequency
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 (Ref. Fig. 12). Turn adiusting screw COUNTERCLOCKWISE
gradually to reduce engine speed until frequency meter indicates 386 Hz.
bderfrequency protective relay should not function to open the load con-
tactor at this frequency. Reduce frequency in steps of 1 Hz.
(b) If the protective system functions to open ihe load contactor and turn on
the underfrequency light after same frequency between 385 Hz and 375 Hz
is reached, al I components of the system are functioning properly. If the
load contactor is not opened within the above functioning range, refer to
Trouble Shooting Chart, 3-2, Figure 6, to determine which component
is defective.
(c) Return unit to normal operating condition.
(41) Check overfrequency sensing relay, protective monitor, and indicating light.
This protective circuit operates in exactly the same manner as the underfrequency
circuit except its operating range is from 415 Hz to 425 Hz.
Its purpose also is
to open the load contactor and turn on an indicating light.
(a) Check procedures are the same for overfrequency as for underfrequency
(above) except that engine speed is INCREASED to create a condition
of over-frequency.