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SPLIT SYSTEMBREAKER
Electrical Power Generating System Simplified SchematicFigure 3
A
747-400
MAINTENANCE MANUAL
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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MAINTENANCE MANUAL
(2)
The BUS TIE switches through GCU internal circuits, trip the bus tie breaker (BTB) (when placed in the ISLN (isolation) position) and closes the BTB (when placed in the AUTO (automatic) position). When the BTB is tripped, either automatically or when the BUS TIE switch is placed in the ISLN position, the ISLN lamp in the BUS TIE switch comes on. When the BTB is closed, the AUTO lamp in the BUS TIE switch comes on and the ISLN lamp goes off. Activation of the GCU automatic bus isolation (autoland) control function also causes a closed BTB to trip. In the autoland mode, the BTB cannot be manually closed and the ISLN lights on the BUS TIE switches are inhibited.
(3)
The DRIVE DISC switches, when pressed, cause a solenoid in the IDG to energize, which starts the disconnect sequence. At the same time, a signal is sent to the GCU to trip the GCR, which trips the GCB. This action isolates the generator from its load. Reconnection of a disconnected IDG is a ground operation only. A DRIVE lamp in this switch comes on when the oil out temperature in the IDG reaches 365 |11°F (185° |6°C) or the charge pressure switch closes. This indicates that the GEN DRIVE DISC switch should be actuated.
NOTE: Airplanes with -10 generator control units:
____ The Drive Light will be illuminated the second time the GCR/GCB trips due to OF/UF protection during a flight.
(4)
The APU GEN switches signal the bus control unit (BCU) to send a signal to the auxiliary generator control unit (AGCU) to open or close its associated auxiliary power breaker (APB). The generator AVAIL light on the switch indicates when the APU generator power quality is within frequency and voltage limits. When the AVAIL light comes on, the APU generator may be selected.
(5)
The IDG GEN FIELD MAN RESET switches close and trip the generator control relay (GCR) in the generator control unit. When the IDG GEN FIELD MAN RESET switch is in the FIELD OFF position, the GCR is tripped and the FIELD OFF lamp comes on. When the IDG GEN FIELD MAN RESET switch is cycled from the FIELD OFF position, the GCR closes and the IDG may be excited. Cycling the IDG GEN FIELD MAN RESET switch again trips the GCR, causing the FIELD OFF lamp to come on. With the GEN CONT switch is in the OFF position, cycling the IDG GEN FIELD MAN RESET switch from the FIELD OFF position excites the IDG without closing the GCB.
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MAINTENANCE MANUAL
(6)
The APU GEN FIELD MAN RESET switches close and trip the generator control relay (GCR) in the auxiliary generator control unit. When the APU GEN FIELD MAN RESET switch is in the FIELD OFF position, the GCR is tripped and the FIELD OFF lamp comes on. When the APU GEN FIELD MAN RESET switch is cycled from the FIELD OFF position, the GCR closes and the APU generator may be excited. Cycling the APU GEN FIELD MAN RESET switch again trips the GCR, causing the FIELD OFF lamp to come on.
(7)
The SPLIT SYSTEM BREAKER (SSB) switch trips or closes the split system breaker (SSB) when cycled. When the SSB is tripped, an OPEN lamp below the switch comes on. This indicates that the SSB is tripped and the electrical power system is split into two independent halves. Cycling the SPLIT SYSTEM BREAKER switch closes the SSB, paralleling the IDGs on both sides of the sync bus. This causes the OPEN lamp to go off. The split system breaker is inhibited in the air mode.
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