Trip values for protective circuits are as follows:
Over voltage relay
Trips at 126 volts after 1-second time delay.
Trips at 140 volts in 160 milliseconds.
Trips at 180 volts in 50 milliseconds.
Under voltage relay
Trips at 100 volts after 7 seconds.
Over frequency relay
Trips at any value between 420-Hz and 480-Hz
after a 5-second time delay. Trips immediately
at any frequency exceeding 480-Hz.
Under frequency
Trips at 380-Hz or less after a 7-second time
delay.
Overload time delay
Trips in approximately 5 minutes at 125% load
on either output or both outputs.
(6)
Generator Set Control PC Board
The generator set control PC board (19, Fig. 6 and Figure 7) is a central location for the various
plug-in relays used for generator operation. Troubleshooting is thus easier for technicians
working on the generator set. This PC board contains the following relays and associated
circuitry.
•
Master relay, K69,
routes 12-V DC power to all circuits, except panel and clearance lights.
This relay is operated upon pressing the START push-button switch
(26, Fig. 5)
, and
remains in the OPERATE condition until it is RESET by the STOP push-button switch
(20,
Fig. 5).
•
Bypass relay, K73,
is also activated by pressing the START push-button switch. Relay
K73 enables the start signal to the starter solenoid for 5 seconds after it is initially
activated. K73 also disables the low oil pressure fault circuit during this 5 second period.
•
Idle-excitation relay, K68
, controls engine speed and generator excitation
.
K68 activates
to idle the engine and remove excitation from the generator. In the RESET state, K68
provides a 12-V DC signal to the governor controller, causing the engine to attain rated
speed (2400 RPM). At the same time, K68 provides a ground signal to voltage regulator,
which enables excitation current to the generator. When the engine is running, K68
changes from OPERATE to RESET, or vice-versa, with each closure of the START
push-button switch. Auxiliary circuit also controls the idle-excitation relay. This auxiliary
circuit causes the relay to operate when: (1) Engine is at rest and the start push-button
switch (26, Fig. 5) is pressed, (2) Any engine fault, except the air filter restriction, occurs.
•
The circuit which controls K68 also drives a flasher circuit that controls the lamp within the
START push-button switch (26, Fig. 5).
•
Relay K72
controls the No. 1 contactor. When the engine is at rated speed, and voltage
has built up, K72 changes from OPERATE to RESET, or vice-versa, with each closure of
the No. 1 contactor push-button switch. An auxiliary circuit will reset K72 when the No. 1
plug is removed from the aircraft. The No. 2 contactor control relay, K272 operates in the
same manner.
•
Relay K70
controls panel and clearance lights. This relay changes from OPERATE to
RESET
, or vice-versa, with each closure of the LAMPS push-button switch (28, Fig. 5)
.
The fuel gage is also powered by K70 when the engine is at rest. K70 is reset, turning off
all lights, when the engine STOP push-button switch is pressed.
OM-2084 / Operation and Maintenance Manual
90CU24 / Series 500392 Generator Sets
Chapter 1-1
November 27/1997
Page 14