Electrical Flashcards
General
2 independent AC and DC systems, each capable of supplying complete power should other system fail via cross ties. Should complete AC or DC failure occur the emergency gen and emergency TRU automatically supply power to emergency and essential busses 24 volt battery for APU starting and supplies DC power for essential services
Main Generators
2 40KVA AC generators provide 200 volt 400Hz 3 phase power Driven by AGB and are cooled by oil from aft transmission With gen switch is ON associated main line contactor closes and connects generator to 3 phase AC bus bar
GCU
Monitors output of its associated generator and provides protection of its system from over/under voltage, under frequency, and busbar faults by automatic control fo generator contactor Contactor opens whenever frequency decreases to 81% RRPM +/- 1.5 RRPM Causes GEN # FAIL light to illuminate when generator is disconnected from its busbar GEN # HOT comes on when internal generator temp rises above 150*C
AC Power Distribution
Consists of: 115/200V 3 phase MAIN AC BUS 115/200V 3 phase ESSENTIAL BUS 115V single phase AC NAVIGATION BUS 26V AC INSTRUMENT BUS 26V AC NAVIGATION BUS No. 1 and 2 AC essential busses are powered by No. 1 and 2 primary buses through No 1 and 2 essential bus relays. If supply fails, emergency gen will pick up load and provide power to the busbars 2 AC transformers provide power to 26V AC instrument busbars and 26V AC navigation busbars If either gen fails, its contactor opens to disconnect it from its busbar and cross tie contactor connects busbar with opposite 3 phase busbar AC BUS TIE cb protects busbar against short circuits occurring in other phase busbar. With AC BUS TIE cb open services supplied from defective busbar are lost
Nav Bus Changeover Switch
Installed on No. 2 PDP to test nav bus changeover relay. Setting switch to No. 2 de energizes 26VAC bus fail relay which in turn de energizes the nav bus changeover relay. This causes No. 2 essential bus bar and 26VAC busbar to energize both No. 1 and 2 115VAC and 26VAC nav buses. Changeover is confirmed by momentary power off warning flags on nav instruments.
AC Essential Bus Fail Annunciator
2 AC ESS BUS caution lights come on when associated essential bus is de energized Essential bus failure is sense by a PHASE SEQUENCE SENSOR within corresponding essential bus failure detector. Sensor de energizes relay in detector and relay contacts ground the associated AC ESS BUS capsule on warning panel
Emergency AC Power
Emergency gen provides 200 volt, 400 HZ, 3 phase AC power. It is mounted on oil cooler fan gearbox and is driven by AFT TRANSMISSION Emergency GCU prevents generator from developing any power unless switch is set to TEST or FLT. A failure of a gen or TRU will cause emergency gen GCU to energize the emergency gen Emergency gen will power emergency 3 phase AC bus. Emergency TRU will provide 28VDC and illuminate EMER GEN READY light. If second main generator fails the essential bus fail relays will connect emergency AC bus to both AC ESS BUSes. If second TRU fails the DC BUS contactor will connect emergency TRU to both DC ESS BUSes
Emergency Gen Switch
Labeled TEST/OFF/FLT At FLT with rotors turning at normal speed the generator is rotating but not providing electrical power. If a main gen or TRU fails, emergency gen reverts to STANDBY mode, develops power, energizes emergency AC bus, emergency TRU, and turns on EMER GEN READY light. If second main gen or TRU fails, emergency gen will energize AC or DC essential and nav buses At TEST, emergency gen is energized by bypassing the emergency gen control circuits. Emergency gen then applies power to emergency bus which also energizes emergency TRU, and illuminates EMER GEN READY light
AC External Power
Female receptacle for external power located forward of left electrical compartment. External power monitor in left electrical compartment checks applied power for over/under voltage and proper phase rotation. If applied power is within specs, monitor will allow power to be connected to system as long as both gen switches are off and EXT PWR switch is set to ON.
DC System
Normally powered by 2 28VDC 200 amp air cooled TRUs powered by main generators. Each TRU supplies power to its respective No. 1 and 2 primary and essential busbars. Each TRU is capable of carrying complete electrical load. When one fails a bus tie relay automatically connects the 2 DC ESS BUS bars. In the event of dual TRU failure the emergency TRU will supply power to emergency and essential DC buses 24VDC lead acid battery is housed in forward LH electrical pod and normally used to start APU
DC Power Distribution
Consists of No. 1 and 2: 26 volt DC BUS 26 volt DC ESSENTIAL BUS 24 volt EMERGENCY DC BUS 24 volt HOT BATTERY BUS TRUs are powered by their respective generators. No. 1 and 2 DC busbars are energized by TRUs through closed contacts of DC contactors which are energized closed by associated TRU. No. 1 and 2 essential busbars are energized by No. 1 and 2 DC BUS bars respectively, through closed contacts of No. 1 and 2 DC ESS BUS contactors If either TRU fails or is turned off, TR1/TR2 FAIL light comes on. DC cross tie circuits will connect failed DC busbar to energized DC busbar to insure continued operation of all DC circuits. Either TRU has capacity to assume entire DC electrical load Upon failure of either TRU the emergency gen will be energized and will not be connected to DC electrical system until second failure of same nature occurs 24 volt battery provides power to HOT BATTERY BUS and will energize DC EMERGENCY BUS when battery is connected AND battery switch on is ON
TRU Hot Annunciators
Labeled TR1/TR2 HOT come on when internal temp of TRU exceeds 150*C TRU will NOT automatically disconnect
Battery Switch
Setting switch to ON energizes battery relay through closed contacts of emergency battery lockout relay and battery overhead relay. The battery relay then energizes the DC emergency bus
BATTERY OFF light
Comes on when battery has been turned OFF (assuming gen/TRUs still powering system)
DC Essential Bus Annunciator
Lights indicate that associated essential DC is de energized Essential bus failure de energizes associated essential bus fail relay which applies a ground to DC ESS BUS capsule on annunciator panel
Battery Switch ON
Normal Configuration
Generator Switches ON - TRU switches OFF
No. 1 Generator Failure
No. 1 Generator Failure - No AC Cross-Tie
Dual Generator Failure
Dual Generator Failure - Open AC Feeder
No. 1 TRU Failure
No. 1 TRU Failure - No DC Cross-Tie
Dual TRU Failure
Dual TRU Failure - Open DC Feeder
AC External Power
DC External Power
