B767
Electrical DO NOT USE FOR FLIGHT
Boeing B767 - Systems Summary [Electrical]
Introduction The electrical system generates and distributes AC and DC power to other airplane systems, and is comprised of: main AC power, main DC power, and battery/standby power. System operation is automatic. Electrical faults are automatically detected and isolated. A hydraulic driven generator operates automatically as a backup source of power in the event that both main AC buses become inoperative.
AC Electrical System The AC electrical system is the main source for airplane electrical power.
AC Electrical System Power Sources The entire airplane AC electrical load can be supplied by any two main airplane AC power sources. The main airplane AC electrical power sources are: • left and right engine integrated drive generators (IDGs) • APU generator. The entire airplane AC electrical load also can be supplied by external power. The power sources operate isolated from one another. Integrated Drive Generators (IDGs) Each engine has an IDG. Each IDG has automatic control and system protection functions. When an engine starts, with the GEN CONT switch selected ON, the IDG automatically powers the respective main bus. The previous power source is disconnected from that bus. The IDG can be electrically disconnected from the busses by pushing the GEN CONT switch to OFF. The IDG can also be electrically disconnected from its respective bus by selecting external power prior to engine shutdown. (See External Power in this section.) The OFF light in the GEN CONT switch illuminates, and the EICAS Advisory message L or R GEN OFF displays whenever the generator control breaker is open.
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Boeing B767 - Systems Summary [Electrical]
The DRIVE light illuminates and the EICAS Advisory message L or R GEN DRIVE displays when low oil pressure or high oil temperature is detected in an IDG. The IDG drive can be disconnected from the engine by pushing the respective DRIVE DISC switch. The IDG cannot be reconnected by the flight crew. APU Generator The APU generator is electrically identical to the IDG generators. The APU generator can power either or both main busses, and may be used in flight as a replacement to an IDG source. If no other power source is available when the APU generator becomes available, the APU generator automatically connects to both main AC busses. If the external source is powering both main busses, the external source continues to power both main busses. The APU Generator OFF light illuminates, and the EICAS advisory message APU GEN OFF displays when the APU is operating and the APU generator breaker is open because of a fault or the APU GEN switch is selected OFF. When the APU GENERATOR switch is ON and a fault is detected, the APU generator cannot connect to the busses. External Power External power can power the left and right main busses. When the power source voltage and frequency are within limits, the external power AVAIL light illuminates. Pushing the EXT PWR switch ON connects external power to both main busses and removes the IDGs and the APU generator from the busses, if they were powering the busses. When external power is connected to a main bus, the EXTERNAL POWER ON light illuminates.
AC Electrical Power Distribution AC power is distributed through the left and right main busses and the ground service bus. AC Main Busses The right IDG normally powers the right main bus and the left IDG normally powers the left main bus. The APU normally powers both main busses when they are not powered by any other source. External power may also be connected and will also power both main busses. Bus tie breakers, controlled by BUS TIE switches, isolate or parallel the right and left main busses. When both BUS TIE switches are set to AUTO, the bus tie system operates automatically to maintain power to both main busses. Page 2
Boeing B767 - Systems Summary [Electrical]
The AC bus ISLN light illuminates and the EICAS advisory message L or R BUS ISOLATED displays when the bus tie breaker is open because of a fault or the BUS TIE switch is OFF. The BUS OFF light illuminates and the EICAS caution message L or R AC BUS OFF displays if an AC bus is unpowered. The source order for powering left and right main busses is the: • respective IDG • APU generator • opposite IDG. Utility Busses Left and right utility busses, powered by their respective main AC bus, are controlled by UTILITY BUS switches. Left and right galley busses are powered by their respective utility busses, and have no direct controls or indicators. The utility bus OFF lights illuminate and the EICAS advisory message L or R UTIL BUS OFF displays when a galley and utility bus are unpowered. Ground Service Bus The ground service bus is normally powered by the right main bus. Alternate sources of power for the ground service bus are: • the APU generator • external power. The ground service bus powers: • the main battery charger • the APU battery charger
• miscellaneous cabin and system loads.
Ground Handling Bus The ground handling bus can be powered only on the ground and only from the APU generator or from the external power source. It is provided for loads such as cargo handling and equipment energized only during ground operations. Autoland During autoland, the busses isolate to allow three independent sources to power the three autopilots: • the left main system powers the left autopilot and the captain’s flight instrument transfer bus • the right main system powers the right autopilot and the first officer’s flight instrument transfer bus • the battery/standby system powers the center autopilot.
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Boeing B767 - Systems Summary [Electrical]
Above 200 feet, loss of a generator results in: • both bus tie breakers closing and the operating generator powers both left and right AC busses • the left main system powers the center autopilot • NO LAND 3 appears on the Autoland Status Annunciator. Below 200 feet, loss of a generator results in: • both bus tie breakers remaining open • the autopilot associated with a failed generator is unpowered • the flight instruments remain powered through the flight instrument transfer busses • the autoland continues using the remaining two autopilots. When the autopilots are disengaged or an autopilot go–around is performed, the electrical system reverts to normal, non–isolated operation. Flight Instrument Transfer Busses Normally, the captain’s flight instruments are powered by the left main AC Bus, and the first officer’s flight instruments are powered by the right main AC Bus. If the respective bus tie breakers are in AUTO, the flight instrument transfer busses transfer to the opposite main AC bus in the event power is lost to a main AC Bus. If power is lost to both main AC busses, the captain’s flight instruments are powered by the hydraulic driven generator. AC Transfer Busses Left and right AC transfer busses power items considered necessary for ETOPS flights, which are not powered by the battery/standby system. Transfer busses are normally powered by their associated main AC busses, but also can be powered by the Hydraulic Driven Generator when both AC busses are unpowered. Electrical Load Shedding Electrical load shedding occurs automatically to ensure power is available to critical and essential equipment. If the electrical loads exceed the power available, the electrical system automatically sheds AC loads by priority until the loads are within the capacity of the generators. The load shedding is galley power first, then utility busses. Utility busses are followed by individual equipment items powered by the main AC busses. When an additional power source becomes available or the load decreases, the electrical system automatically restores power to the shed systems (in the reverse order).
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Boeing B767 - Systems Summary [Electrical]
Examples of load shedding that may be observed during normal operations include: • an electric hydraulic pump prior to engine start • center tank fuel pumps prior to engine start • utility busses during engine start. Examples of load shedding that may be observed during non–normal operations include: • utility busses after a generator failure • center tank fuel pump after an engine failure • cabin ceiling lights after an engine failure. On the ground, advancing the thrust levers into the takeoff range with the engines shut down may cause inadvertent load shedding of the utility busses to occur. Returning the thrust levers to idle, then pushing the UTILITY BUS switches OFF, then ON will reset this inadvertent load shedding.
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Boeing B767 - Systems Summary [Electrical]
AC Electrical System Schematic (Hydraulic Driven Generator) APU GEN EXT PWR O F F
BUS TIE AUTO
ON
ON BUS TIE
AVAIL
AUTO
ISLN
ISLN UTILITY BUS L
R
ON
ON
OFF
OFF
L BUS BUS OFF
L GEN CONT
O F F
L
ON
R BUS BUS OFF
GEN DRIVE DISC
DRIVE
R GEN CONT
R
DRIVE
O F F
ON
HYDRAULIC DRIVEN GENERATOR TO STANDBY AC BUS
LEFT MAIN AC BUS
LEFT AC TRANSFER BUS
RIGHT AC TRANSFER BUS
CAPT FLT INSTR TRANSFER BUS
F/O FLT INSTR TRANSFER BUS
RIGHT UTILITY BUS
LEFT UTILITY BUS APU
TO BATTERY CHARGERS GROUND SERVICE BUS
GEN APU GEN CONTROL SWITCH
GROUND HANDLING BUS
LEFT BUS TIE
LEFT GEN CONTROL
RIGHT MAIN AC BUS
EXTERNAL POWER SWITCH
RIGHT BUS TIE RIGHT GEN CONTROL
LEFT DRIVE
PRIMARY POWER SOURCE
RIGHT DRIVE
SECONDARY OR BACKUP POWER SOURCE
DC Electrical System The main DC electrical system uses transformer–rectifier units (TRUs) to produce DC power. The TRUs are powered by the main AC busses. Page 6
Boeing B767 - Systems Summary [Electrical]
The TRUs operate isolated from one another. If one TRU fails, the DC bus tie breaker closes to keep both DC busses powered. Both BUS TIE switches must be in AUTO for the DC bus tie breaker to close. There are no flight deck controls for the main DC electrical system.
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Boeing B767 - Systems Summary [Electrical]
DC Electrical System Schematic APU GEN EXT PWR O F F
BUS TIE AUTO
ON
ON
BUS TIE
AVAIL
AUTO
ISLN
ISLN UTILITY BUS L
R
ON
ON
OFF
OFF
L BUS BUS OFF
L GEN CONT
O F F
L
ON
R BUS BUS OFF
GEN DRIVE DISC
DRIVE
R
DRIVE
R GEN CONT
O F F
ON
TO STANDBY DC BUS
BATTERY BUS
LEFT MAIN DC BUS
RIGHT MAIN DC BUS
MAIN BATTERY
T
DC BUS TIE BREAKER
TRU
TRU
FROM LEFT AC BUS
PRIMARY POWER SOURCE SECONDARY OR BACKUP POWER SOURCE
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FROM RIGHT AC BUS
Boeing B767 - Systems Summary [Electrical]
Battery/Standby Power System The battery/standby power electrical system can supply DC and AC power to selected flight instruments, communications and navigation systems, and other critical systems, if there are main AC and DC electrical power system failures. The Battery/Standby Power System consists of the following busses: • the hot battery bus • the battery bus • the standby AC bus • the standby DC bus
Hot Battery Bus The hot battery bus provides power to items which must be continuously powered, such as the clock’s time reference. Prior to establishing electrical power, the main battery powers the hot battery bus. After establishing electrical power, the main battery charger powers the hot battery bus.
Battery Bus Prior to establishing electrical power, when the battery switch is ON, the main battery powers the battery bus. After establishing electrical power, the left DC system powers the battery bus, and the main battery provides a backup source of power. The Battery DISCH light illuminates when the main battery is discharging. If EICAS is powered, the advisory message MAIN BAT DISCH also displays. The battery OFF light illuminates and the EICAS advisory message BATTERY OFF displays if the battery switch is OFF after electrical power is established.
Standby DC Bus The standby DC bus can be powered by several sources. Prior to establishing electrical power, when the battery switch is ON and the standby power selector is in AUTO, the main battery powers the standby DC bus. The Battery DISCH light illuminates when the main battery is discharging. After establishing electrical power, the left DC system powers the standby DC bus and the main battery provides a backup source of power. When the standby power selector is in BAT, the main battery powers the standby DC bus. The standby bus OFF light illuminates and the EICAS advisory message STANDBY BUS OFF displays if the standby DC bus is not powered.
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Boeing B767 - Systems Summary [Electrical]
Standby AC Bus The standby AC bus can be powered by several sources. Prior to establishing electrical power, when the battery switch is ON and the standby power selector is in AUTO, the main battery powers the standby inverter which provides AC power to the standby AC bus. After establishing electrical power, the left AC system powers the standby AC bus and the main battery and standby inverter provide a backup source of power. When the standby power selector is in BAT, the main battery and standby inverter power the standby AC bus. The standby bus OFF light illuminates and the EICAS advisory message STANDBY BUS OFF displays if the standby AC bus is not powered.
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Boeing B767 - Systems Summary [Electrical]
Battery/Standby System Schematic (FROM THE GROUND SERVICE BUS) BATTERY CHARGER
BAT
STBY POWER AUTO
ON
HOT BATTERY BUS MAIN BATTERY
D I S C H
BAT
OFF
OFF
O F F
STANDBY DC BUS STANDBY AC BUS
BATTERY BUS L MAIN DC BUS
BATTERY CHARGER
BAT
L MAIN AC BUS
STBY POWER AUTO
ON
HOT BATTERY BUS
I S
BAT
OFF
OFF
O F F
INV
MAIN BATTERY
STANDBY DC BUS STANDBY AC BUS
BATTERY BUS L MAIN DC BUS BATTERY CHARGER
BAT
L MAIN AC BUS
STBY POWER AUTO
ON
HOT BATTERY BUS MAIN BATTERY
I S C H
BAT
OFF
OFF
O F F
INV
STANDBY DC BUS STANDBY AC BUS
BATTERY BUS L MAIN DC BUS
L MAIN AC BUS
LIGHT ILLUMINATED FLOW LINES NOT ON PANEL: DC POWER FLOWING DC POWER NOT FLOWING
AC POWER FLOWING AC POWER NOT FLOWING
Hydraulic Driven Generator The hydraulic driven generator (HDG) activates automatically when both the left and right main AC busses are unpowered. The Hydraulic Driven Generator (HDG) is powered by the Center Hydraulic System. Page 11
Boeing B767 - Systems Summary [Electrical]
The HDG provides AC power to: • the left AC transfer bus • the right AC transfer bus • the standby AC bus (through the left AC transfer bus) • the captain’s flight instrument transfer bus The HDG provides DC power to: • the hot battery bus • the battery bus • the standby DC bus. The amount of DC power produced by the HDG is less than the DC power produced by a fully charged battery. When the HDG first begin to operate, the battery DISCH light may illuminate, until the battery power decreases to the power level produced by the HDG.
Battery/Standby System Schematic (Hydraulic Driven Generator Operating)
BAT
BATTERY CHARGER
STBY POWER AUTO
ON
HOT BATTERY BUS MAIN BATTERY
D I S C H
OFF
OFF
O F F
BATTERY BUS L MAIN DC BUS LEFT TRANSFER BUS HYDRAULIC DRIVEN GENERATOR RIGHT TRANSFER BUS
FLOW LINES NOT ON PANEL: DC POWER FLOWING DC POWER NOT FLOWING
BAT
CAPT FLT INSTR TRANSFER BUS
AC POWER FLOWING AC POWER NOT FLOWING
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STANDBY DC BUS STANDBY AC BUS
Boeing B767 - Systems Summary [Electrical]
Electrical EICAS Messages The following EICAS messages can be displayed. Message
Level
L AC BUS OFF
Caution
BUS OFF
APU GEN OFF
Advisory
OFF
APU generator control breaker is open due to a fault with the APU running.
BATTERY OFF
Advisory
OFF
Battery switch is OFF.
L BUS ISOLATED
Advisory
ISLN
Bus tie breaker is open due to an AC electrical system fault.
Advisory
DRIVE
Generator drive oil pressure is low or generator drive oil temperature is high.
Advisory
OFF
Generator control breaker is open.
MAIN BAT DISCH
Advisory
DISCH
Main battery is discharging.
STANDBY BUS OFF
Advisory
OFF
Standby AC or DC bus is unpowered.
L UTIL BUS OFF
Advisory
OFF
Galley and utility busses are unpowered.
R AC BUS OFF
Light
R BUS ISOLATED L GEN DRIVE R GEN DRIVE L GEN OFF R GEN OFF
R UTIL BUS OFF
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Aural Beeper
Condition AC Bus is unpowered.
Boeing B767 - Systems Summary [Electrical]
Electrical Panel 8
1 APU GEN EXT PWR
2
O F F
BUS TIE
3 4
AUTO
ON
9
ON BUS TIE
AVAIL
AUTO
ISLN
ISLN UTILITY BUS L
R
ON
ON
OFF
OFF
L BUS BUS OFF
5
L GEN CONT
6 7
O F F
L
ON
10
BUS OFF
12
GEN DRIVE DISC
DRIVE
11
R BUS
R
R GEN CONT
DRIVE
13 O F F
ON
14
OVERHEAD PANEL 1
APU Generator (APU GEN) Control Switch
ON (bar in view) – • arms APU generator breaker to automatically close. OFF (bar not visible) – • opens APU generator breaker • resets fault trip circuitry. 2
APU Generator OFF Light
Illuminated (amber) – • the APU generator breaker is open because of a fault with APU running • the APU generator control switch is selected OFF.
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Boeing B767 - Systems Summary [Electrical] 3
BUS TIE Switches
AUTO – • arms automatic AC bus tie circuits • arms automatic DC bus tie circuits • arms automatic flight instrument transfer bus circuits. OFF (AUTO not visible) – • commands the AC bus tie open • commands the DC bus tie open • commands the flight instrument bus tie open • resets fault trip circuitry. 4
AC Bus Isolation (ISLN) Lights
Illuminated (amber) – • a fault has occurred, automatically opening the AC bus tie breaker • the BUS TIE switch is OFF. 5
AC BUS OFF Lights
Illuminated (amber) – the AC bus is unpowered. 6
Generator Control (GEN CONT) Switches
ON (bar in view) – arms the generator breaker to close automatically when generator power is available. OFF (bar not visible) • opens generator breaker • resets fault trip circuitry. 7
Generator OFF Lights
Illuminated (amber) – the generator breaker is open. 8
External Power (EXT PWR) Switch
Push – if AVAIL light is illuminated, closes external power contactor Subsequent push – opens external power contactor. 9
External Power ON Light
Illuminated (white) – external power is powering the bus(es).
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Boeing B767 - Systems Summary [Electrical] 10
External Power Available (AVAIL) Light
Illuminated (white) – external power is plugged in and power quality is acceptable. 11
UTILITY BUS Switches
ON (bar in view) – if no load shed signal is present, connects utility and galley busses to main AC bus. OFF (bar not visible) – • disconnects utility and galley busses from main AC bus • resets overload load shed circuitry. 12
Utility Bus OFF Lights
Illuminated (amber) – the utility and galley busses are unpowered. 13
Generator Drive Disconnect (GEN DRIVE DISC) Switches
Push – • disconnects generator drive from the engine • requires maintenance action on the ground to reconnect the generator drive. 14
Generator DRIVE Lights
Illuminated (amber) – • the generator drive oil temperature is high • the generator drive oil pressure is low.
Battery/Standby Control Panel 4
1
BAT 2 3
ON D I S C H
STBY POWER AUTO OFF BAT
OFF
O F F
OVERHEAD PANEL
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5
Boeing B767 - Systems Summary [Electrical] 1
Battery (BAT) Switch
ON – • Unpowered airplane on the ground: • a few annunciator lights illuminate • allows the APU to be started • Powered airplane inflight or on the ground when AC power is removed or lost: • the standby and battery busses are powered. OFF (ON not visible) – turns battery power off. 2
Battery OFF Light
Illuminated (amber) – the battery switch is off. 3
Battery Discharge (DISCH) Light
Illuminated (amber) – the main battery is discharging. 4
Standby (STBY) POWER Selector –
OFF – the standby busses are unpowered. AUTO – the standby busses transfer to battery power if normal AC power is lost. BAT – the standby busses are powered from the main battery. 5
Standby Power Bus OFF Light
Illuminated (amber) – standby AC or DC bus not powered.
Hydraulic Generator Test Switch
1
HYD GEN
ACCESSORY PANEL 1
Hydraulic Generator Test Switch
Spring-loaded to center. HYD GEN – initiates hydraulic driven generator system test. Page 17
