ARMY TM 9-6115-604-12
NAVY NAVFAC P-8-633-12
circuit inside K114. The anode of the SCR (K114 terminal 7) is tied to the positive terminal of the battery in the
generator set start circuit. When gated on the SCR cathode (K114 terminal 12) energizes a slave relay, K10 Relay
K10 energizes self-latching annunciator alarm relay A1K9 and circuit breaker trip relay K30. Annunciator horn LS1
sounds and OVERCURRENT fault light A9DS9 on the annunciator panel flashes. Relay K30 energizes the trip coil
in load circuit breaker CB101, opening the breaker to disconnect generator G1 from the bus. The engine will
continue to run, but load circuit breaker CB101 cannot be closed until the annunciator alarm system has been
manually reset via ANNUNCIATOR RESET pushbutton S12 on the upper door of cabinet A. To protect generator
G1 from the possibility of a dead short across its output lines, overcurrent relay K114 has a second SCR (SCR-B)
parallel connected to that described above. Gating of this SCR is controlled by the INST dial on the front panel of
the relay. The dial is normally set at “3” with its associated vernier, marked ADJ, set fully counterclockwise.
Instantaneous tripping of K114 occurs when input current rises to current pickup tap setting (4 for each phase)
multiplied by the INST factor (normally set at "3”). Hence, an input current of 12 amperes on any phase will
instantaneously trip the relay, whereas a time delay of about 2.5 seconds would transpire if only SCR-A were in the
circuit to trip the relay . (A12 ampere input would represent a 420 ampere line current. Such a current might
damage generator G1 if applied as long as 2 5 seconds ). After SCR-B trips the relay, slave K10 is energized, and
events proceed as described above.
(6) GROUND FAULT Relay K115. GROUND FAULT relay K115, panel mounted on upper cabinet A door, is an
overvoltage relay configured for ground fault detection in conjunction with ground fault transformer T100 and ground
fault resistor assembly R100. Both of the latter are located in the rear section of cabinet A. The neutral phase of
generator G1 (TO) is tied to generator set ground through the primary of ground fault transformer T100. Ground
fault resistor assembly R100 is connected across the secondary of T100. GROUND FAULT relay K115 senses the
voltage across R100. The relay trips when voltage across R100 increases to a value determined by a tap block in
the relay. The tap plug, located at the top of relay K115, behind the plastic cover, is normally set in the "A"
position. The time dial, centered and just below the tap, is normally set to “1". These settings result in contact
closures within 1 second. If the relay senses 28 V ac or more across R100 28 V ac across R100 corresponds to a
ground fault potential of 506 V ac at 0 92 ampere across the primary of T100. When GROUND FAULT relay K115
is topped, it energizes a slave relay, K11 Relay K11 energizes self-latching annunciator alarm relay A11K2 and
circuit breaker trip relay K30. Annunciator horn LS1 sounds and GROUND FAULT light A9DS11 on the annunciator
panel flashes. Relay K30 energizes the trip coil in load circuit breaker CB101, opening the breaker to disconnect
generator G1 from the bus. The engine will continue to run, but load circuit breaker CB101 cannot be closed until
the annunciator alarm system has been reset via ANNUNCIATOR RESET pushbutton S12 on the upper door of
cabinet A.
(7) Synchro Check Relay K116. Synchro check relay K116 is located inside the upper part of cabinet B. When
manually paralleling the generator set with an energized bus, synchro check relay K116 is used in conjunction with
SYNCHROSCOPE M106 and SYNCHRONIZING LIGHTS DS110 and DS111 to ensure that load circuit breaker
CB101 is not closed until the voltage, frequency, and phase of generator G1 and the bus are in close agreement.
When PARALLEL Switch S6 is set to PARALLEL, parallel relay K4B is energized to place SYNCHROSCOPE
switch S115 in the arming circuit for load circuit breaker CB101. When SYNCHROSCOPE SWITCH S115 is set to
ON, SYNCHROSCOPEM106 is actuated. SYNCHRONIZING LIGHTS DS110 and DS111 flash to show voltage
differences between generator G1 line L1 and bus line L1, and generator G1 line L2 and bus line L2, respectively.
Synchro check relay K116 senses bus line L1, and generator line L1. All elements sense bus voltage through bus
instrument transformers T108 (line L1 ) and T109 (line L2). Generator G1 lines are sensed through generator
instrument transformers T104 (line L1) and T107 (line L2). The generator instrument transformers are high
accuracy (0 6 percent) 20:1 step-down transformers. To parallel the generator set with the bus, the operator checks
for proper phase connections using PHASE SEQ. SEL. SW S119, then adjusts the voltage and frequency output
of generator G1 using VOLT ADJ rheostat R101 and FREQ ADJ rheostat R102. SYNCHROSCOPE M106 and
SYNCHRONIZING LIGHTS DS110 and DS111 indicate to the operator when the generator set is ready to parallel.
Synchro check relay K116 ensures generator G1 output agrees with the bus by preventing load circuit breaker
CB101 closure until the difference between the generator output voltage and bus voltage is less than 5 percent, the
difference between the two frequencies is less than 0.5 hertz, and the phase angle between the two voltages is less
than a pre-set value between 6 and 18 degrees (normally 10 degrees). When these three conditions are met, relay
K116 energizes and arms the closing circuit for load circuit breaker C8101. If the operator then sets BREAKER
CONTROL SWITCH S4to CLOSE, the breaker will close to connect generator G1 to the bus. Synchro check relay
K116 will also energize when voltage is sensed at generator G1, but not at the bus. This “dead bus" feature
enables load circuit breaker CB101 closure to connect generator G1 to a dead bus. When OPERATION
SELECTOR SWITCH S3 is set to AUTO, Synchro check relay K116 is removed from the load circuit breaker
CB101 arming circuit and breaker closure Is controlled by synchronizer A105.
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