Electrical Flashcards
AC power sources
Primary:
2 engine driven Integrated Drive Generators (IDGs)
40 KVA, 115V(AC), 400HZ
Alternate:
APU Generator
40 KVA, 115V(AC), 400HZ
Emergency:
ADG (Air Driven Generator)
15 KVA, 115V(AC), 400HZ
Intergrated Drive Generators (IDG)
Consist of a generator and constant speed drive integrated into one unit
Purpose: To take variable N2 engine speed and convert it to constant 12,000 RPM generator speed.
The integrated drive is a hydro-mechanical device that is driven by the variable speed, engine accessory gearbox which uses an integral oil system to drive the generator at a constant speed.
The oil is cooled by an air/oil heat exchanger that uses air from the N1 fan as the cooling medium. If the IDG oil overheats or oil pressure drops below limits, the IDG switchlight FAULT lamp of the switchlight illuminates.
APU Generator runs at a constant speed, no IDG needed
AC Buses are:
– BUS 1
– BUS 2
– ESS BUS
– SERV BUS
Generators are:
– 40 kVA rated IDGs
– 40 kVA APU generator
- Any generator can support an entire AC load
AC external service switch
• switch/light pressed on external AC service panel
• gives limited power for aircraft servicing
• this is the service configuration normally used online
• do not need battery master switch ON
Air Driven Generator ADG
- automatically deploys when AC BUS 1 and 2 lose power
• manually deploys when the ADG Manual Deploy Handle is pulled
• powers the ESS BUS, HYD Pump 3B, slats/flaps, and STAB TRIM CH 2 - After Power is reestablished to a main generator, the PWR TXFR OVERRIDE switch must be pushed to transfer power
Emergency AC power is supplied to the aircraft by a deployable Air-Driven Generator (ADG), when the normal electrical power sources become inoperative. The ADG is controlled and protected by an Automatic Deployment Control Unit (ADCU), a dedicated GCU and separate ACPC circuitry.
The ADG system is installed on the right side of the aircraft nose. It is designed to be automatically deployed in flight from its stowed position when both AC Bus 1 and AC Bus 2 are not powered. If the automatic deployment feature fails to operate, the ADG can be deployed manually with the manual deployment release handle located at the bottom of the center console.
When deployed the ADG delivers three-phase, 115/200 volt, 400 hz power to a segregated department within the ACPC. This power is then distributed to the flaps, slats, pitch trim and hydraulic 3B pump, and to the AC Essential Bus. Once powered, the AC Essential Bus powers ESS TRU 1, which in turn provides DC power to the DC Essential and DC Battery buses (DC ESS Tie closes).
NOTE
Between 160 and 155 KIAS, the Essential DC Bus is load shed causing the loss of the ESS TRU 1 and 2, XFLOW pump, the left probe heaters, ice detection and window heat.
To prevent the occurrence of “ADG stall” the aircraft must be configured no later than 140 KIAS.
AC Power Center (ACPC)
AC power is distributed to the aircraft sub-systems through the AC power center (ACPC). The ACPC contain system power contactors, current transformer assemblies and circuit breakers for the purpose of switching AC power to the appropriate electrical bus.
In addition, the ACPC provides secondary power distribution to hydraulic pumps, flaps and slats and pitch trim circuits via circuit breakers and relays/ contactors that are controlled by their specific system control units.
APU
Started by the main battery.
The APU generator supplies AC electrical power to the aircraft buses during ground operations with the engines off. The APU generator can be used to power the buses in flight should an engine generator fail.
The APU generator output is 115-volt AC, 400-Hz, and is rated at 40 KVA from sea level up to 41,000-feet.
Generator Fault Protection
The auxiliary GCU controls, monitors and provides protection and voltage regulation for the APU generator.
The auxiliary GCU in conjunction with ACPC and the primary GCUs provide bus priority logic during normal and non-normal operations.
The APU generator output is tripped off and removed from the bus system for one of the following conditions:
• over and under voltage
• over and under frequency
• generator and bus over current • generator phase sequence
AC receptacle
External Power Monitoring
A three-phase, 115/200 volts, 400 hz, AC power receptacle is provided on the right forward fuselage, just below the external service panel.
External power monitoring is provided within the ACPC and with an external power monitor (EPM). The EPM monitors the power provided from the ground unit. If the power is determined to be acceptable the green AVAIL portion of the AC – AVAIL/IN USE switchlight will illuminate. If the external power does not meet prescribed limitations of voltage, frequency and phase the AVAIL portion of the switchlight will not illuminate.
AC AVAIL/IN USE Switchlight
External Service Panel AC Switchlight
The AC AVAIL/IN USE switchlight in the flight deck permits 115 VAC external power to be supplied to the aircraft AC power system.
An external AC switchlight is available on the external service panel. It’s function is identical to that of the AV AVAIL/IN USE switchlight in the flight deck Electrical Power control panel, with one exception.
Depressing the external AC switchlight allows external power to be applied to the aircraft in the Service Configuration, which supplies AC power to the AC Service Bus only.
AC Electrical Power Distribution Description:
115 volt AC electrical power from the aircraft generators and APU generator is distributed via the ACPC to the four AC buses. Electrical power is supplied to the buses by routing the power through the ACPC and four circuit breaker panels. Two circuit breaker panels are installed on the flight deck. The other two are located in the aft equipment bay and unpressurized nose compartment.
Fault protection of the bus system and automatic generator/bus transfer is carried out by a series of electrical relays within the ACPC. This automatic fault protection and transfer system constitutes the bus priority system.
Monitoring of system status is done using the EICAS AC synoptic page. The aircraft AC bus system consists of the following four buses:
• AC BUS 1 (Main)
• AC BUS 2 (Main)
• AC ESS (Essential) BUS
• AC SERV (Service) BUS
The ADG BUS is part of the emergency AC power system. It is not depicted on the EICAS AC synoptic page.
AC Bus 1 and AC Bus 2
AC BUS 1 and AC BUS 2 are the main AC buses of the aircraft. AC BUS 1 is located behind the pilots seat on circuit breaker panel No.1 (CBP 1). AC BUS 2 is behind the co-pilots seat on CBP 2. The main AC buses receive power from any of the three aircraft generators or from external AC power. AC BUS 1 supplies the electrical power to the AC ESS BUS. AC BUS 2 normally feeds the AC SERV BUS.
Bus protection is provided by the ACPC and the generator GCUs and other electrical relays. The electrical relays within the ACPC determine the bus priority system.
Bus Priority
AC BUS 1 and AC BUS 2 are critical buses and are protected by the bus priority logic to ensure that the buses remain powered at all times. The priority protection is provided by a series of electrical relays within the ACPC.
The bus priority for AC BUS 1 is:
• GEN1
• APU generator
• GEN2
• External power
The bus priority for AC BUS 2 is:
• GEN2
• APU generator
• GEN1
• External power
AC Essential Bus
The AC ESS BUS supplies the equipment essential for flight. The AC ESS BUS powers ESS TRU 1 that produces DC power for the DC ESS BUS. Under certain specific conditions, the AC ESS Bus will also provide AC power to ESS TRU 2.
AC ESS BUS is normally powered by AC BUS 1. Failure of AC BUS 1 is sensed by the ESS BUS automatic transfer system and the AC ESS BUS is automatically transferred to AC BUS 2. Should it become necessary to manually transfer the ESS BUS, the AC ESS XFER switchlight on the Electrical Power control panel is pressed. This connects the ESS BUS electrically to AC BUS 2.
When AC power is lost during flight, the ADG is deployed. The AC ESS
BUS is powered by the air driven generator and is latched to the ADG BUS. When an aircraft generator power is re-established, pressing the PWR TXFR OVERRIDE button on the ADG CONTROL panel de-energizes the latch relay between the AC ESS BUS and ADG BUS. This allows the AC
ESS BUS to re-establish its normal connection to AC BUS 1 or AC BUS 2.
AC Service Bus
Service Configuration
The AC SERVICE BUS is supplied 115-volts AC from AC BUS 2. The AC SERVICE BUS provides power to service outlets for passenger cabin and lavatory cleaning.
The AC SERVICE BUS may also receive electrical power from the external AC electrical system when in a service configuration.
Connecting external AC electrical power in the external receptacle illuminates the AVAIL lamp in the EXT AC PUSH switchlight on the external services panel and the AC switchlight on the EPCP. If no other AC electrical power is supplying the AC buses, pressing the EXT AC PUSH switchlight on the external service panel allows external AC electrical power to energize only the AC SERVICE BUS. The service configuration allows the aircraft to be cleaned without energizing all the other AC buses.
Selecting any generator to ON or connecting the external power to the buses overrides the service configuration and normal bus configuration is resumed.
Generator Control Unit (GCU)
Controls and monitors the generators and provides protection and voltage regulation for each generator
GCU protection removes generator output for:
over/under voltage
over/under frequency
generator or BUS overcurrent
generator phase sequence
Each generator control unit (GCU) controls and monitors the related AC generator system and provides protection and voltage regulation for its engine generator. The GCUs in conjunction with the AC power center provide bus priority and protection during normal and non-normal operations.
ADG Control Unit (ADGCU)
The ADG control unit performs generator control functions and provides system protection when power is required from the ADG. A generator ready-to-load (RTL) signal is provided to the ACPC when power quality from the ADG is within limits. A built-in test can be initiated by using the test button on the ADG control panel located at the base of the center console.
The GCU continuously performs the following function: • ADG output voltage regulation
• provides generator ready-to-load signals
• flap, slat and pitch trim transfer relays
• ADG line contactor
• hydraulic pump 3B transfer contactor
• monitors ADG output frequency and voltage
The GCU ensures protection against the following abnormal operating conditions:
• over voltage
• under frequency
• over frequency
• feeder fault
Auto Deploy Control Unit (ADCU)
The ADCU provides the following operations:
• automatic deployment of the ADG (power lost on AC Buses 1 and 2 in flight).
• uses the GCU RTL signals to operate the ADG line contactor.
• provides system BITE, Power Up BIT and Initiated BIT (tests integrity of internal circuits and the uplock solenoid coil).
Automatic Deployment Logic
All of the following conditions must exist before the ADGCU will command ADG deployment.
• AC Bus 1 and AC Bus 2 power sense inputs fall below 50 volts
• weight on wheels system indicates that the aircraft is airborne
• any aircraft generators were on line for at least 3.45 seconds prior to the loss of power on AC Buses 1 and 2
Initiated BIT Switch and Annunciator Light
The ADGCU conducts continuous self-tests once power is applied to the aircraft. Failure by the ADGCU will be accompanied by related EICAS Status messages.
The ADG Initiated BIT switch is used for maintenance purposes to verify the interface between the ADCU and associated systems. A successful test will illuminate the Test Status Indicator Light (green).
If tested on the ground the Test Status annunciator light will illuminate 2 seconds after test initiation and will stay illuminated for 2 seconds. If tested in flight it will illuminate 5 seconds after initiation of the test for 2 seconds. Non-illumination of the annunciator indicates that the ADCU has failed the BIT.
Direct Current (DC) System Description
DC electrical power from four transformer rectifier units (TRUs) and two nicad batteries is distributed, via two DC Power Centers Left and Right DCPC) to nine DC buses.
There are in effect, two separate DC distribution systems. The TRU system carries the majority of the DC electrical loads and the battery system provides emergency power in flight and allows the APU to be started on the ground.
Electrical power is supplied to the buses by routing the power through the DCPCs and four circuit breaker panels. Two circuit breaker panels are installed in the flight compartment. The remaining two are located in the aft equipment bay and the forward unpressurized nose compartment. DC power distribution is controlled from the EPCP and DC TIE contactors located within the DCPCs.
Monitoring of system status is done using the EICAS DC synoptic page. The aircraft DC bus system consists of the following nine
buses:
- DC BUS 1 (Main)
• DC BUS 2 (Main)
• DC ESS (Essential) BUS
• DC SERV (Service) BUS
• DC UTIL (Utility)
• DC BATTBUS (Battery)
• DC EMERG BUS (Emergency) - MAIN BATT DIRECT BUS
• APU BATT DIRECT BUS
TRU Distribution
The normal source of 28-volts DC electrical power for the DC system is provided by the four TRUs. Each TRU transforms then rectifies the supplied 115-volt AC electrical power to create unregulated 28-volt DC. The TRUs are rated at 120 amps.
The four TRUs are:
• TRU 1 normally supplies BUS 1
• TRU 2 normally supplies BUS 2 and UTIL BUS
• ESS (essential) TRU 1 normally supplies the ESS BUS
• ESS (essential) TRU 2 normally supplies the ESS BUS
DC batt bus
The DC BATT BUS supplies the equipment essential for safe flight. The DC BATT BUS is normally powered by ESS TRU 2. The bus is protected in a number of ways. Should ESS TRU 2 fail, ESS TRU 1 can be used to power the DC BATT BUS. If all TRU power is unavailable, the bus can be powered directly from the MAIN BATT DIR BUS and the APU BATT DIR BUS.
During ADG operation, the AC ESS BUS powers ESS TRU 1 that in turn powers the DC BATT BUS through the ESS TIE contactor.
DC SERV BUS
DC UTIL BUS
The DC SERV BUS supplies electrical power to supply lighting for the passenger cabin and the external navigation lights. It is normally powered by the TRU 2 through DC BUS 2.
The DC UTIL BUS provides reading lights at the passenger service units. The utility bus is powered by TRU 2. Should TRU 2 or TRU 1 fail, the utility bus is automatically load shed to reduce the DC electrical loading. Loading shedding is controlled by the right PC with the MAIN TIE contactor.
DC Contactors
The DCPCs have five power contactors that are used, when needed, to ensure that the DC buses remain powered. The opening and closing of these contactors in an automatic function of the DCPCs. Contactor status is monitored and displayed by the EICAS system on the DC Electrical synoptic page.
Main Tie Contactor
The MAIN TIE contactor is used to connect DC Bus 1 and DC Bus 2 in parallel. It will be closed by DCPC 2 (right) for a number of DC system conditions. When closed, the DC UTIL Bus is automatically load-shed.
Essential Tie Contactor
The ESS TIE contactor is used to connect the DC BATT Bus and the DC ESS in parallel. It will be closed by DCPC 1 (left) for a number of DC system conditions.
Cross Tie Contactor
The CROSS TIE contactor is used to interchange the power from TRU 2 with the ESS TRU.
TRU Contactor Control
The function of the TRU contactors is to isolate the distribution system following a feeder fault between the TRU and the associated DCPC. Each TRU has a contactor inside its DCPC (TRU 1 and ESS TRU 1 in the left DCPC and TRU 2 and ESS TRU 2 in the right DCPC).
ESS TRU Transfer Contactor
The ESS TRU Transfer Contactor is used to switch the power source of ESS TRU 2 from AC Bus 2 to the AC ESSENTIAL Bus. This contactor is normally NOT displayed on the DC Electrical synoptic page, and is used in two specific scenarios.
• following the loss of ESS TRU 1 while the aircraft is powered by the ADG
• when the aircraft is not ADG powered and AC Bus 2 and TRU 1 are unpowered.
Service Bus Contactor Control
The DC Service Bus contactor is used to connect the APU BATTERY DIRECT BUS to the DC SERVICE BUS. The contactor is energized when the DC Service switch on the Electrical Power control panel is selected ON. The DC Service Bus is also energized when the aircraft is in the service configuration.
