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The electrical system is 115/200V 400Hz 3 phase AC and 28V DC system capable of coping with transients. Commercial supply is secondary. 2 / 1 generators are/is required to supply all buses. The system will auto-reconfigure and can dispatch with 1 GEN inop. 2 Electrical Contactor Management Units (ECMUs) provide AC/DC contactor control, galley shedding control, NBPT control, monitoring and indication: their failure opens bus ties but leave the GENs on line as the later have a hold-on relay. An ECMU1 fault leaves the APU GEN shed. The No Break Power Transfer function avoids power interruptions during source switching on the ground in normal configuration; it is inhibited in flight. (The NPBT may be reset by a total power-down OR by resetting the GPCU DC c/b Q6 in the avionics bay, panel 721). Synchronisation usually takes milliseconds but may take up to 15secs for APU transfer. On the A340 a single remaining GEN supplies its own side. In flight, there is no parall eling of supplies. All buses auto-connect but require manual isolation. 2 EXT supplies may be connected. An Emergency GEN is driven by the HYD system or RAT and automatically provides emergency power in the case of the loss of AC bus 1 -1 / 1 and 2-4 / 2 or (obviously) of all main aircraft GENs (the RAT will extend with the loss of engines 1 and 4 / both). All circuit breakers are in the electrical equipment bay and are not for resetting in flight; an ECAM C/B page is provided. If both APU GEN and EXT A are connected, the APU has priority has priority for the left side and EXT A has priority for the right side. c EXT AC power supplies are 90kVA supplies (EXT A on the right, B: left). IDGs are cooled by a fuel/oil, air/oil heat exchanger. On the groun d, the GND SELECT CTL switch (on the forward C/B panel on the ceiling behind the flight-deck) allows electrical buses to be energised by EXT A without supplying the entire aircraft for lighting, fuel indications/refueling, ground call, park brake and cargo door operation. The APU generator is rated at 115kVA. The 4 / 2 engine GENs are driven from the engine accessories gearbox through their IDGs and are rated at 75 / 115 kVA. The EMER GEN delivers 5.5 / 8.6 kVA when powered by the HYD system but only 3.5kVA when powered by the RAT below 260kt. A static inverter transforms DC voltage from the DC ESS bus into single phase AC supplied to part of the AC ESS bus at 2.5kVA. In flight, this auto -reconfigures when only batteries are supplying the aircraft regardless of BATT pb switch position. On the ground, it is activated similarly but requires both BATT switches to be ON. Each AC bus is supplied in priority order by its engine GEN, the APU GEN or EXT A, EXT B, the other engine GEN on the same side ( -- ) or the other side outer engine GEN. Note that for the APU to power the aircraft, the BUS TIE pb must be AUTO otherwise the APU GEN is separated from the AC 1 & 2 buses [1.24.10 p2 & 3.02.24 p16] Considerable changes have clearly taken place to the AC reconfiguration logic since the Get-Well program and less is now lost with a single GEN out although the ECAM will still display Galley Partly Shed. The Galley can be fully restored by resetting the Galley pb. The 2 main 37 Ahr batteries are permanently connected to the 2 hot buses. With AUTO selected, the batteries are connected to the DC BAT BUS if the battery voltage < 26.5V or, on the ground, if only the batteries are supplying the aircraft. The main batteries are connected to the DC BATT bus only if charging is required otherwise they are connected to the DC ESS bus when selected ON. The BCLs control battery charging and illuminate the c light illuminates for thermal runaway or short circuit. The batteries are connected to the DC ESS BUS wh en only the batteries are supplying the aircraft in flight or, on the ground, provided BOTH battery pb are selected to AUTO. A third battery is dedicated to the APU. 2 main TRU (200A) and one essential TRU (100A) permanently provide DC supply from the AC buses. A further TRU (100A) is dedicated to APU start or APU battery charging. 2 identical ECMUs provide AC/DC contactor control, galley shedding control, No Break Power Transfer and monitoring/indication. Normally:
AC 1 bus powers ESS TR and TR 1 and AC ESS bus thence ESS TR powers DC ESS bus, TR 1 powers DC 1 thence DC BAT bus. AC 2 bus powers TR 2 and APU TR bus thence TR 2 powers DC 2 bus and APU TR powers DC APU bus thence APU BAT bus. A340: AC1-2 bus powers TR 1 bus which powers DC 1 bus. AC2-3 bus powers TR 2 bus which powers DC 2 bus. Abnormally: if AC 1 (1-1) fails, AC 2 (2-4) powers AC ESS bus and ESS TR. AC 2 (2-4) is then latched to the AC ESS even if AC 1 (1-1) is resupplied. if ALL AC *-* buses fail, EMER GEN powers AC ESS. when only batteries are supplying the aircraft whatever the BATT 1/2 pb position, DC ESS powers the Static Inverter which pow ers AC ESS bus. if TR 1 fails, TR 2 powers the DC BAT bus thence DC 1 bus, and vv. if ESS TR fails, TR 1 powers DC BAT bus thence DC ESS bus. if both TR 1 & ESS TR fail, TR 2 powers DC BAT bus thence DC 1 but the DC ESS bus is lost, and vv for TR2. The loss of the D C ESS bus will initially cause a higher level caution than the initial TR failure and a secondary *F/CTL alert. c Lights: Batteries - thermal runaway or short circuit, AC ESS feed - not electrically supplied, GALLEY - overload detection without autoshedding, IDG - oil outlet overheat or oil low pressure (inhibited N2<14%), GEN - GCU protection trip (if initiated by a differential fault, the reset action has no effect after 2 attempts), APU GEN - as GEN but inhibited at low APU speed, If a GEN/TR is lost due to overcurrent detection, reconfiguration does not happen and the related AC BUS and DC BUS is lo st. TR indication goes for abnormal voltage/current values, overheat or short circuit. TR voltage goes 25V>V>31V, current doesnƎt change. BATT voltage goes 25V>V>31V, current goes >5A. GEN load goes >108% for >10secs, GEN voltage goes 110V>V>120V, GEN freq goes 390Hz>Ø>410hz. IDG oil temperature pulses at 142°C, called an ECAM ADV at 151°C/ °C and is turns at 185°C. The IDG should be shut down for an OVHT or LO PR (the LO PR is inhibited at N2<14 %). If the IDG pb is depressed for more than 3secs, damage is caused. IDG disconnect is inhibited when the engines are not running. If the IDG is disconnected in flight (ECAM !), it can only be reconnected on the ground. ECAM !" message against the DC or AC bus means that the ESS SHED bus is not supplied. A340: A single failed generator is replaced by other generator on the same wing. 2 failed GENs on opposite wings are individually replaced by the other generator on the same wing. 2 failed gen erators on the same wing are replaced by the outer generator on the other wing. 3 failed generators cause the loss of 2 AC buses on one wing. In all cases the APU GEN will, if available, replace the lost generator s.
A330: A single failed generator on one side is replaced by that on the opposite wing. Loss of both GENs can be replaced by the APU GEN. If the aircraft will not accept external AC supplies, disconnect the external supplies, select both the EXT A and B pb ON mom entarily, then deselect both pb. Reconnect the external power supplies and try again [QRH Reset of Computers ATA 24]. The EMERG ELEC Generator auto-starts if AC 1 & 2 (AC 1-1 and 2-4) are lost and it supplies the AC ESS bus. It can be manually selected if there is no auto-start. # appears on the memo display. If AC1 -1 and 2-4 were lost due to engine 1 & 4 failure, the RAT will be extended and power the EMER GEN, in which case it will be inhibited at slat extension. The EMER GEN FAULT light is ON when the emergency generator is not supplying and normal AC is lost in flight. In EMERG ELEC config the EL/AC page (when forced onto the E/WD) displays !" to the right of the AC ESS box if the AC ESS SHED bus is not supplied and -300 c$% if that pb has been pushed. The EM ER GEN remains latched to the AC ESS bus even after recovery of AC busses through alternative supplies. EMER GEN deactivation occurs only automatically in fl ight at slats extension (to ensure sufficient hyd pressure) if engines 1 and 4 / both are lost (MAN pb reactivates EMER GEN after slat retraction) or, on the ground, after engines 1 and 4 / both are shutdown. A number of extra items are available to cover ETOPS on the A330 such as FMGC1, HF1, SEC2, ADR3, WAI, WHC1, ND1, Capt AoA/pitot, Stby AoA/pitot, anti-skid and wx radar. AP function requires 2 ADIRS active [1.22.30 p8] so no AP is available on the A340 but IS on the A330 until ADR3 is lost when LAND RCVRY pb is pressed. A330 Flight with RAT powering hyd system and LAND RCVRY pb pushed.
or COMMERCIAL or OFF or GALLEY PARTIALLY SHED
Only if NO AC generation
The EMER GEN supplies are as per the table:
AC ESS AC ESS SHED AC ESS GND
Critical Busbars status when the Emergency Generator is powered by: Engine RAT Flight, Batts only Flight, Batts only Ɠ Ɠ
Ground, Batts only Ɠ
Ɠ <50kt
via ESS TR DC ESS DC ESS SHED DC BATT
lost after 7 secs
lost after 7 secs <50kt Whatever the LAND REC pb position tbd not shed Ɠ Ɠ -300 tbd tbd Ɠ = through the static inverter.
via LAND REC pb LAND REC SHED LAND REC AC LAND REC DC
In EEC, all LAND RECOVERY AC and DC BUS bars are shed. The LAND RECOVERY pb when pressed recovers the AC/DC LAND REC buses, which restores the LGCIU 1, SFCC 1 (NB Flap channel Ƌ therefore flap - is not recovered if the EMERG GEN is powered by the RAT or on batteries) and ILS 1. The remaining fuel pump (if any, should fail at <260kt or at LAND REC selection) is lost and, contrary to the F COMs, is not now replaced by the forward APU pump. On the A330, also restored are BSCU 1, LH windshield anti-ice (is not recovered if the EMERG GEN is powered by the RAT or on batteries), LH landing light, while HF1, ADR3 (ergo AP 1) and Wx radar 1 are lo st. Autobrake lost due only one PRIM. If ENG 2 and IDG 1 failed, no flaps. Gravity gear extension is required to protect the RAT from the hyd demand of gear lowering. The ECAM approach config of FLAP 3 appears to presume recovery of the hyd to power the EMER GEN. Flight Critical Items In Emerg Elec Config PRIM/SEC 1 are powered by DC ESS or, if that fails, the Hot Batt bus. The Capt's PFD and the E/WD are powered by the AC ESS. The Standby AI and Compass are powered by the DC ESS. The Standby Alt imeter is powered by the DC ESS SHED. Only the Capt's pitot probe is heated by the AC ESS (so the standby ASI may be unreliable). Only VHF1/RMP1 is operative, powered by DC ESS. SSR channel 1 only is powered by AC ESS: TCAS is dead. The crew oxygen control is powered by the DC ESS SHED. The right dome light illuminates only on the ground from the DC ESS. The centre instrument panel lighting and standby compass light are powered by the DC ESS . The essential system for the annunciator lights is powered by the AC ESS. If EMER EXIT LT is at ARM, the cabin emergency lights illuminate when normal aircraft electrical power or DC ESS bus fails and overhead emergency lights come on if AC 1 fails. No exterior lights are available. For flight on batteries, all normal and standby pumps are lost and post-mod 44603 no APU pumps start. FCTM Ch8 offers good advice on the controllability, nav and comms. Loss of PRIM/SECs affect flight control architecture, see QRH 5.03.
c:\Ɩ\24ELEC.doc - created: 13 January 1995 - last saved: 21 December 2008
