(b)
Five conditions can trip (open) a GCB: 1) Pressing the GEN CONT switch off (out); 2) pressing the appropriate guarded GEN DRIVE DISC switch on M10063; 3) pulling the engine fire switch on aft pilots' control stand P8; 4) a protective trip by the GCU (Ref 24-23-00); or 5) an engine shutdown. If external power is available, pushing the EXT PWR switch on M10063, also trips the GCBs. External power then supplies main ac bus power (Ref 24-41-00). Any of these conditions cause the GCU to send 28-volts to the GCB trip coil. When the GCB opens, its GEN CONT switch amber OFF light comes on. If the corresponding engine is on, a level C EICAS message also appears: L (or R) GEN OFF. If the GEN DRIVE DISC switch is pressed, the amber DRIVE light in this switch comes on.
(c)
A GCB is reset after a protective trip by cycling its GEN CONT switch. The GEN CONT switch is first pressed to off (out), then to ON (in). If the amber OFF light comes on again, the GCB is still open. (The fault condition remains.) The OFF light in the GEN CONT switch may thus be on at the same time that the switch is in the ON position. The light indicates GCB position. The switch directs the GCB to close if the GCU allows it. A protective function may not allow the GCB to close.
(3)
Bus Tie Breaker (BTB) Control (Figs. 4 and 5)
(a) The left and right BUS TIE switches on the M10063 panel control their respective BTBs. Each switch is a push on/push off type, which latches in when on. When latched, an AUTO indicator in the switch is visible. An amber ISLN light is also in the switch.
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MAINTENANCE MANUAL
TRIP
28V DC
OABAT BUS
PMG L/R GEN
OB
115V AC
CONT UNIT
OAOB
LEFT BUSP6
OC
OC
INPUT
SPEED
SENSOR
R
AUTO
INTEGRATED DRIVE GENGEN CONT
HOT BUS WRN
LT L/R GEN TRIP
UNIT
ISLN
POWER
L/R BUS TIE SW CLOSE
SUPPLYL/R BUS TIEBREAKER
PROTECTIONBUSSYSTEM
W
OFF
TRIP
UNDERSPEED
TRIPL/R BUS OFF LIGHT
GCR COMMANDGCR CLOSED CLOSEON O
IR/L BUS TEI
OFF
ON
UBREAKER
GCB
NTP
PRIORITY
P
UU
T
ON W
T
OFF
PNL LTUNDERSPEED TRIP
II
EPC
N
T
NCLOSE
O
EPC ONMD&TT
EPC
E
TO GNDGCB CONTROL
FA
CLOSE
F
E
RGND MODE
LOGIC RELAYSCLOSE
RR/L GEN CKT
FBTB SW F
BREAKER BTB LOCKOUT
AA
LEFT/RIGHT GENC
L/R GEN CONT SWCCIRCUIT BREAKER
E BTB RIGHT/LEFT GEN POWER PANEL
E ELEC SYS CONT PANEL
DEAD MAIN BUS L/R GCB AUX CONTDIGITAL
L/R GCU DIGITAL LINK (+)DATA
DATA LINKLINK
OPENXCVR
L/R GCU DIGITAL LINK (-)
DATA LINK
L/R GEN OFF
LEFT/RIGHT GEN CONTROL UNIT
BUS POWER CONT
(LEVEL C ALARM) CLOSEL/R AC BUS OFF
EXT PWR (LEVEL B ALARM)
LEFT/RIGHT EICAS
COMPUTER
TRIP
CLOSEL/R GCB TRIPISOL DIODE
AUX PWR
APU/EXT POWER PANEL
Left/Right Generator Circuit Breaker Control Schematic
Figure 3
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(c)
(d)
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MAINTENANCE MANUAL
The object of the BTBs is to avoid a power loss on either main ac bus. If a main bus loses power, its BTB closes. The main ac bus is then connected to the ac tie bus. This allows the main bus to receive alternate power from: 1) An external power source, 2) the APU generator, or 3) the other main generator. (The numbers correspond to alternate source priority. Each main bus generator always has highest priority.)Each generator control unit (GCU) contains separate BTB close and trip relays. The GCU in the APU position does not control either BTB. The left and right GCU control their respective BTB. To close a BTB, the GCU close relay sends 28-volts dc to the BTB close coil. To open a BTB, the GCU trip relay sends 28-volts dc to the BTB trip coil.Normally, both BUS TIE switches are set to AUTO (in). The position of the BTBs is then determined by GCU logic and wiring between the power breakers. If each main ac bus is supplied by its generator the BTBs are open. The main ac buses are isolated from each other, and the ac tie bus. The ISLN lights in the BUS TIE switches will not be on. An ISLN light only comes on due to a system fault, or the corresponding BUS TIE switch being in the out position.If the main ac buses are not energized, the battery switch must be ON for automatic BTB control. The BAT switch is on the standby power panel M10062. (This panel is on P5.)Both BTBs close if one generator circuit breaker (GCB) opens, and no auxiliary or external power is available. (The auxiliary power breaker (APB), and the external power contactor (EPC), are open.) The one operating generator supplies both main ac buses. Both BTBs also close if both GCBs open. Any available source then supplies the main buses.With a GCB open, its associated BTB closes. Any available source supplies power to the main ac bus. This BTB opens, if its GCB closes. The BTB actually opens before its GCB closes, to prevent parallel source operation. However, the BTB remains closed if the APB, EPC, and the other GCB are open. The one operating generator then supplies power to both main ac buses. If the APB, EPC, or other GCB are to close, the BTB is opened first. Power sources cannot be paralleled. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 电源 ELECTRICAL POWER 1(60)
