Protective Circuit - Hobart 120CU20 Operation And Maintenance Manual With Illustrated Parts List

OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
Trouble, Symptom,
Condition.

Protective Circuit

NOTE: Protective monitoring is not completely functional until the load contactor is CLOSED. Since it is not
advisable to vary voltages for test purposes while delivering power to an aircraft, the GPU should be
connected to a load bank for trouble shooting protective circuits. To avoid repetition, it will be assumed that
"TEST/RESET" push-button switch has been pressed and the load contactor has been closed before
commencing each test.
1. Load contactor opens
during power delivery.
Over voltage fault
indicated.
2. Load contactor opens
during power delivery.
Under voltage fault
indicated.
October 15, 2013
Probable Cause.
a. Over-voltage condition
may have been result
of a sudden drop in
load, or possible
tampering with REG
potentiometer, and
may have been a
normal action.
b. Defective CTL board.
a. Under-voltage
condition may have
been result of a sudden
shock load, or possible
tampering with REG
potentiometer, and
may have been a
normal action.
b. Defective CTL board.
Test, Check, and/or Remedy.
Press "TEST/RESET" push-button switch and
resume power delivery. Observe voltmeter to be
certain voltage is normal 115 VAC. Adjust to
normal if necessary. If load contactor is opened
again and the fault code meter indicates an over-
voltage condition, proceed to step b.
Use REG potentiometer to reduce voltage to 110
VAC. Observe voltmeter and gradually increase
voltage with potentiometer. If sensing circuit CTL
board functions to open load contactor at any value
less than 125 VAC, it is defective. Replace CTL
board.
Press "TEST/RESET" push-button switch and
resume power delivery. Observe voltmeter to be
certain voltage is normal 115 VAC. Adjust to
normal if necessary. If load contactor is opened
again and the fault code meter indicates an under-
voltage condition, proceed to step b.
Use REG potentiometer to reduce voltage to 100
VAC. Observe voltmeter and gradually decrease
voltage with potentiometer. If sensing circuit CTL
board functions to open load contactor at any value
great than 100VAC, it is defective. Replace CTL
board.
Chapter 2-4
Page 16