ARMY TM 9-6115-604-12
NAVY NAVFAC P-8-633-12
Speed switch SS1/SS2/SS3 is connected to the tachometer drive on the engine fuel pump and senses
engine speed at all times. When engine speed rises above 600 rpm, SS1 trips to simultaneously connect
battery positive to M7 pin A and disconnect battery positive from M7 pin 4. Loss of battery positive at K7
pin 4 results in loss of power at M7 pin 7, crank relay K3 deenergizes and starter motors B1 and B2 are cut
off as described in step (5), above. The engine will rapidly continue to accelerate under its own power.
SS2 will close when engine speed reaches 1200 rpm. Thereafter, shutdown relay K14 is self-latching if
EMERGENCY SHUTDOWN pushbutton S7 is pressed or MASTER SWITCH S9 is set to STOP while
engine speed is above 1200 rpm. When the relay is energized, the normally closed contacts of relay K14
open to cut off battery positive from the DC control circuits. Crank timer relay M7 Is Inhibited, preventing
the operator from attempting to restart the engine while it is freewheeling at 1200 rpm or higher. The
operator should wait until the engine comes to a complete halt before restarting.
Engine speed stabilizes at 1500 rpm (50 hertz operation) or 1800 rpm (60 hertz operation) Engine speed is
controlled thereafter by load sharing module A104.
15 to 25 seconds after the appearance of battery positive at M7 pin A (refer to step (6), above), battery
positive appears at M7 pin B to energize relays K17A and self-latching relay K17B. Normally open
contacts of K17A close to arm oil pressure shutdown relay K18. A second set of normally open K17A
contacts close to arm undervoltage annunciator fault relay A10K8, low oil pressure annunciator fault relay
A10K2, and underfrequency annunciator fault relay. All K5 Battery positive remains available at K7 pin B
for about 40 seconds, then switches off with no effect upon the circuitry.
The engine will continue to run at operating speed until manually shut down (refer to step f, below) or
automatically shut down by a protective circuit (refer to step d, below). Control of of the engine at
operating speeds is accomplished via the AC power generation and electrical control circuits. Refer to
paragraph 4-32 for details.
Generator Set Protective Circuits. There are nine fault sensors used to monitor conditions in the engine, cooling
system, lubricating system, and fuel system. They are the fuel level switches FL3 and FL4; oil pressure alarm
switch OP2, and oil pressure shutdown switch OP1, high oil temperature switch OT2, overspeed switch SS3,
coolant level switches S13 and S14; coolant temperature warning switch WT2, and coolant temperature
shutdown switch WT1. On a fault condition, these sensors cause a warning to be displayed to the operator.
Additionally, some of them cause a generator set shutdown. These sensors function In the DC control circuit as
Low Fuel Level Switch FL3. Low fuel level switch FL3 is mounted through the top of the generator set fuel
tank and is accessible through the floor of the control room. FL3 will close on a low fuel condition to energize self-
latching relay A10K5 in the annunciator alarm system. Annunciator horn LS1 sounds and annunciator panel light A9DS5
flashes while the generator set continues to run. A10K5 also energizes low fuel level time delay relay K23. After a
preset time delay (normally 35 minutes) relay K23 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 n 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. Theoretically, low fuel level fault shutdown will not occur because the operator will replenish the
generator set fuel supply and reset the alarm circuit before the time delay (normally 35 minutes) elapses. Note that If the
operator replenishes the fuel supply, but fails to reset the alarm circuit via ANNUNCIATOR RESET pushbutton S12, low
fuel level time delay relay K23 will still time out and cause a generator set shutdown. The operator will not be able to
reset the alarm circuit before replenishing the fuel, but failure to reset the circuit after refueling will result in a shutdown.
The purpose of this circuit is to back up the fuel transfer system circuit. If the fuel transfer system circuit is operational
and set to AUTO, low fuel level alarm relay A10K5 will not trip. If the generator set is connected to an adequate external