ARMY TM 9-6115-604-12
NAVY NAVFAC P-8-633-12
(2)
High Fuel Level Switch FL4 High fuel level switch FL4 is mounted through the top of the generator set fuel
tank and is accessible through the floor of the control room FL4 will close on a high fuel condition to
energize self-latching relay A 10K6 in the annunciator alarm system. Horn LS1 sounds and annunciator
panel light A9DS6 flashes while the generator set continues to run. A10K6 will energize high fuel level
fault slave relay K5. Relay K5 will open its normally closed contacts to deenergize fuel pump contactor
K13. Transfer pump contactor K13 will open its normally closed contacts to cut off 120 V ac from fuel
transfer solenoid L102 and fuel transfer pump contactor K106. Contactor K106 will deenergize, cutting off
240 V ac from fuel transfer pump motor B102. Solenoid valve L102, deenergized will close to block the
fuel inlet line, preventing any more fuel from entering the generator set fuel tank. This protection circuit
primarily prevents overfilling of the generator set fuel tank by gravity feed (siphoning) from the external
fuel supply. Secondarily, the circuit guards against fuel transfer system "runaway" which could occur if
high fuel level float switch FL2 failed to open upon a high fuel level condition.
(3)
Oil Pressure Alarm Switch OP2. Oil pressure alarm switch OP2 is mounted on the right end of the lube
filter head assembly. To allow time for oil pressure to build up in the engine block, the low oil pressure
alarm circuit is not armed until 15 to 25 seconds after engine speed has exceeded 600 rpm. Oil pressure
in the engine block causes the normally closed switch OP2 to open. If oil pressure should fall below 37 to
41 psi (255 to 283 kPa) during engine operation, OP2 will close to energize self-latching relay A10K2.
Annunciator horn LS1 sounds and annunciator panel light A9DS2 flashes while the generator set continues
to run. The operator is expected to investigate the cause of the low oil pressure warning. Generally, the
cause will be insufficient crankcase oil in the engine. Failure to find and correct the cause of the warning
may result in a generator set shut down caused by oil pressure shutdown switch OP1.
(4)
Oil Pressure Shutdown Switch OP1. Oil pressure shutdown switch OP1 is mounted on the right end of the
lube filter head assembly (OP1 and OP2 are in the same housing). To allow time for oil pressure to build
up in the engine block, the oil pressure shutdown circuit is not armed until 15 to 25 seconds after engine
speed has exceeded 600 rpm. Oil pressure in the engine block causes normally closed switch OP1 to
open. If oil pressure should fall below 28 to 32 psi (193 to 221 kPa) during engine operation, OP1 will
close to energize oil pressure shutdown relay K18. Relay K18 will energize fault shutdown relays K20A
and K20B Relay K20A deenergizes self-latching engine run relay K15B. As a result, engine fuel solenoid
L1 loses power, closes, and cuts off fuel to the engine; the engine shuts down. Relay K20B energizes
circuit breaker trip relay K30. Relay K30 energizes the trip coil in load circuit breaker CB101, opening the
breaker to disconnect generator G1 from the bus. The generator set cannot be restarted until the
annunciator alarm system is reset via ANNUNCIATOR RESET pushbutton S12 on the upper door of
cabinet A.
(5)
Oil Temperature Switch OT2. Oil temperature switch OT2 is mounted on the left side of the engine oil
pan. If the oil temperature in the engine sump rises to 242 to 248°F (117 to 120 C) or higher, the normally
open switch OT2 will close to energize self-latching relay A10K4 in the annunciator alarm system.
Annunciator horn LS1 sounds and annunciator panel light A9DS4 flashes.
(6)
Overspeed Switch SS3. Overspeed switch SS3 is connected to the tachometer drive of the engine fuel
pump, which is located on the left side of the engine. Overspeed switch SS3 senses engine speed at all
times. If engine speed uses above 2200 rpm, the normally open contacts of switch SS3 will close to
energize overspeed shutdown relays K19A and K19B. Relay K19A energizes fault shutdown relays K20A
and K20B and air shutdown solenoids L2A and L2B. Relays K20A and K20B shut down the generator set
as described in step (4), above. Solenoids L2A and L2B close the air control valves to cut off air to the
engine air intake manifolds. Relay K19B energizes self-latching relay A10K1 in the annunciator alarm
system. Annunciator horn LS 1 sounds and annunciator panel light A9DS1 flashes. With both fuel and air
cut off, the engine shuts down. Solenoids L2A and L2B remain energized only as long as engine oil
pressure keeps normally open air shutdown solenoid disconnect switch OP3 closed. OP3 serves to
automatically deenergize solenoids L2A and L2B after the engine shuts down. This automatic
deenergization is required because solenoids L2A and L2B are not rated for continuous duty. Once an
overspeed fault shutdown occurs, the engine can be restarted only after the fault circuit is reset through
the ANNUNCIATOR RESET switch on generator control cabinet A and the two air control valves mounted
near the turbocharger are manually reset to the open positions and the speed switch button is reset.
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