¡ 2 independent AC systems which cannot be paralleled (each AC system has 1 MAIN + 1 UTILITY Bus) ¡ 1 automatic BUS TIE system is controlled by 2 switches : it ties the MAIN AC Busses together to allow 1 generator to power both busses (APU or External power can also supply both AC busses through the bus tie system) ¡ DC power normally comes from 2 Transformer Rectifiers Units (TRUs) which are powered by their respective MAIN AC busses. If AC power is not available to operate the TRUs, then either the HMG or the MAIN BAT provides DC power (APU battery only provides power for the APU) ¡ STANDBY AC, STANDBY DC and BATTERY busses supply power to essential Flight Instruments + equipment (these busses can be powered from several different busses)
2. AC POWER Integrated Driven Generator (IDG) ¡ Each engine has 1 IDG. (1 CSD + 1 Generator = 1 IDG controlled by 1 generator control switch + 1 generator drive disconnect switch). ¡ When an engine starts (with GEN CTRL switch ON) respective IDG feeds its own MAIN AC bus. - the previous power source is disconnected from that bus - If a MAIN AC bus loses power, its BUS OFF light comes on. ¡ Each IDG can be electrically disconnected from the busses by pushing the GEN CTRL switch to OFF (IDG can also be electrically disconnected from its respective bus by selecting EXT. power). APU Generator ¡ APU generator is electrically identical to the IDG generators & can power either or both Main buses - controlled by APU generator control switch (arms APU generator breaker to open & close automatically). - If no other power is available when the APU generator becomes available, APU generator connects automatically to both Main buses - the OFF light is inhibited when APU selector is OFF. External Power ¡ External Power is connected to the MAIN busses through the bus tie system using the external power switch. - External Power has always priority. - External power must be manually selected but is automatically removed by respective generator. EXT PWR ON AVAIL
- PUSH : if AVAIL light illuminated, closes or opens external power contactor - ON (white) : power contactor is closed - AVAIL (white) : external power available, power quality is acceptable (Ground handling bus is also powered) Copyright Smartcockpit.com
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3. AC DISTRIBUTION ¡ AC power is distributed through the LEFT & RIGHT Main buses + the Ground Service bus AC Main Buses ¡ LEFT IDG normally powers LEFT Main bus / RIGHT IDG = RIGHT Main bus ¡ Bus Tie breakers controlled by BUS TIE switches, isolate or parallel the RIGHT & LEFT Main busses. - when both BUS TIE switches are set in AUTO = bus tie system operates automatically for both Main busses. ¡ Source order for powering LEFT & RIGHT Main busses : - respective IDG - APU generator - opposite IDG Utility Busses ¡ LEFT & RIGHT Utility busses (powered by their respective Main AC bus) are controlled by UTILITY BUS switches. ¡ LEFT & RIGHT Galley busses are controlled by their respective utility bus
Ground Service Bus ¡ GND SERVICE BUS is normally powered by the RIGHT MAIN AC (no flight deck control) ¡ It can be also powered by the GND HANDLING BUS if RIGHT MAIN AC not powered and it is controlled at the FWD F/A panel ¡ It powers : - 2 Battery chargers (MAIN + APU) - Equipment cooling fan - LEFT forward pump - Main entry door - Passengers lights
. PUSH : if RIGHT MAIN AC bus is unpowered, the ground service bus connects to, or disconnects from, APU or external power.
. LIGHT (white) : - illuminated when ground service bus is connected to APU or external power. - extinguished when bus is unpowered or connected to the RIGHT MAIN AC bus.
Ground Handling Bus ¡ GND HANDLING BUS is only powered on ground by APU or Ext. Power directly when power available. - Cargo handling equipment - Cargo doors - Engine cowl doors - Cargo compartment lights - Fueling equipment
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Autoland / Autopilots ¡ During autoland OPS, the busses isolate to allow 3 independent sources to power the 3 A/Ps ¡ 3 A/P powered by their respective busses :
- LEFT A/P on LEFT MAIN system - RIGHT A/P on RIGHT MAIN system - CENTER A/P on CENTER system
¡ Centre system : - normally powered by the LEFT MAIN AC and DC - in case of COUPLED ILS approach, powered by STBY AC and HOT BAT BUS (DC) ¡ Generator failure during COUPLED ILS approach : - above 200 ft RA Ô Both Bus tie breakers closing & the operating generator powers both L&R AC busses Ô LEFT Main system powers CENTER A/P Ô NO LAND 3 - below 200 ft RA Ô Both Bue tie breakers remaining open (Center A/P remain on STBY and HOT) Ô no power on the affected A/P nor the associated main AC Bus Ô in this case : ISLN light + BUS OFF light + both UTILITY Busses off Ô the Flight instruments remain powered thru the flight instrument transfer busses Ô the autoland continues using the remaining 2 A/Ps - after A/P disconnect or during auto G/A = same as above 200 ft RA
Loadshedding ¡ Before start with one AC source available (with Center or LEFT electric hydraulic pump ON) - Galley OFF (no indication) Ô Reset automatically when respective BTB opens or when all hydraulics pumps are switched OFF Ô if necessary, UTILITY Buses (OFF indications) have to be reset manually ¡ During start = utility and galleys trips with engine start selector to GND (both for N°1, affected for N°2) Reset Auto with generator ON or engine start selector trips to AUTO ¡ Starting the other engine = only the affected overloaded side is shed ¡ During takeoff (T/L advanced) or in FLT = loss of one generator causes both utility and all galley buses to trip off (UTILITY BUS lights ON) disregard the load. - Reset automatically in flight with a second generator coming on line - Reset on ground with 1 or 2 T/L retarded and by recycling the Utility Bus switches ¡ Inflight engine shutdown : - respective centre fuel pump - all cabin indirect ceiling lights + forward direct ceiling lights - offsets the hydraulics system requirement for additional power to operate demand pump
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4. AC POWER FAULTS L/R GEN CONT
O F F
ON
DRIVE =
BUS OFF
- ON (bar in view) : closes gen. field & generator breaker arms when proper power available - OFF (blank) : opens field + generator breaker and resets fault trip circuitry - OFF (amber) : generator breaker is open
(amber) = low oil pressure or high oil temperature in an IDG
(amber) = Bus Tie Breaker is locked open because switch is OFF or Fault occurred
BUS TIE - AUTO : arms automatic AC & DC Bus tie closure system - OFF (blank) : opens DC Bus tie breaker + prevents associated flight instruments bus from transferring to alternate power source + resets fault trip circuitry - ISLN (amber) : Bus Tie breaker is locked open because switch is OFF or fault occurred
AUTO ISLN
APU GEN O F F
ON
- ON (bar in view):closes APU gen. field & generator breaker arms when proper power available - OFF (blank) : opens field + generator breaker and resets fault trip circuitry - OFF (amber) : generator breaker is open
UTILITY BUS L
R ON
OFF
ON
OFF
- ON (bar in view) : if no load shed, connects Utility & Galley busses to Main AC bus - OFF (bar not visible) : 1) disconnects Utility & Galley busses from Main AC bus 2) resets overload shed circuitry
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5. DC POWER ¡ LEFT DC bus supplies BATTERY bus + STANDBY DC bus. ¡ MAIN DC busses are not normally interconnected. If 1 MAIN DC bus becomes unpowered, DC BTB closes automatically to repower it from the other MAIN DC bus (not possible if AC bus tie switch not in AUTO) Hot Battery Bus ¡ Prior to establishing electrical power, the Main battery powers the Hot battery bus. ¡ After establishing electrical power, 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, LEFT DC system powers the battery bus & Main battery provides a backup source of power.
Standby DC & AC busses ¡ STANDBY buses power many essential instruments and systems - Standby Power selector OFF : cuts off all sources of power to the STANDBY AC + STANDBY DC busses - Standby Power selector AUTO : Left DC + AC power have priority to supply STANDBY AC + DC busses With battery switch ON, MAIN BATTERY + APU BATTERY + BATTERY CHARGERS act as back-up power for STANDBY AC + DC busses. - Standby Power selector BAT : cuts off MAIN AC + DC power to the standby system. The only power remaining for the STANDBY system is BATTERY power Battery chargers are also cut off With BATTERY switch ON, batteries supply standby DC + AC through the the static inverters.
5. DC POWER FAULTS BAT -
ON
-
OFF
ON : provides APU + MAIN batteries as backup power source for BAT + STANDBY busses if LEFT MAIN DC is lost OFF (blank) : disconnects battery bus from hot battery bus OFF (amber) : battery switch is OFF
MAIN BAT DISCH
(amber) : MAIN battery is discharging. :
APU BAT DISCH
(amber) : APU battery is discharging.
STBY POWER O F F
(amber) : Standby AC or DC bus not powered.
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6. HYDRAULIC DRIVEN GENERATOR (HDG) ¡ In flight, starts automatically in case of loss of BOTH AC Busses (powered by CENTER hydraulics system). ¡ Produce power to - Battery Bus and Hot Battery Bus - LEFT and RIGHT AC Transfer busses - Captain's Instrument Transfer bus - Standby AC & DC busses ¡ F/O instruments are not powered ¡ Not operating while the gear is retracting ¡ AC TRANSFER BUSSES
LEFT STBY AC Bus LEFT FMC and CDU DME IRS HF ATC transponder Angle of attack Heat LEFT pneumatic Isolation Valve CPT Pitot heat RIGHT Aux. Pitot heat Pressure Cont. AUTO 1 Flap/Rudder trim indicator Lights - Aisle stand limited pax - Overhead panel lights - some lavatories
RIGHT Cargo Heat Override control
RIGHT pneumatic Isolation Valve
Pressure Cont. AUTO 2 Limited passenger cabin lighting
¡ LEFT INSTRUMENT TRANSFER BUS - LEFT ADI/HSI/alti/mach-airspeed ind./EFIS control panel / VSI / ILS/ radioaltimeter / instruments & panel lights. - LEFT and CENTER symbol generators
7. INITIAL POWER SETUP ¡ Battery switch ON / Check :
- DISCHARGE light OFF - STBY POWER OFF light ON (this means STANDBY AC or DC not powered)
¡ STBY POWER AUTO / Check : - OFF light extinguishes (this arms the system for transfer of power to the BATTERY, STBY AC & STBY DC busses).
8. EICAS ¡ UPPER is on the LEFT AC BUS
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