Electrical Systems Flashcards
Describe the main batteries.
Two 24-volt, 28 amp-hour, lead-acid batteries
Describe the starter generators.
Two, 28-volt DC, 300 amp (400 amps for up to 2 mins) brush-type starter-generators, one for each engine and an additional starter-generator in the APU.
What do the four additional batteries run?
Avionics
Standby Instruments
Emergency lights
How is current distributed to the aircraft systems?
Via the split bus bar system
What is the polarity of the DC power and what is the return path?
Positive polarity
Return via the low-resistance bonded airframe
What device stabilizes the bus bars and at what voltage?
Generator Control Unit
28.5V
With the generators online, what does the BUS TIE switch allow you to do?
Enables the system to be paralleled or split into two single-channel systems.
What occurs when a bus bar protection unit detects an under- or over-voltage condition?
Automatic splitting of the BUS TIE
Batteries 1 and 2 or normally connected how?
In parallel but can be manually selected to provide DC supply for essential services
DC power is distributed through what buses?
The split bar bus system (PS1 and PS2) and two essential system bus bars (PE1 and PE2).
When are all DC bus bars available?
When any generator is on line or with external 28-volt power connected.
Are the split bus bars (PS1 and PS2) available when running on battery power? Why?
No. This arrangement is required in order to restrict loads on the batteries until such time as a generator (Main or APU) comes on line.
With only one generator on line, what must the BUS TIE be set to IOT power PS1 and PS2?
BUS TIE must be CLOSED
What supplies power to the inverters and what do the inverters supply power to?
Inverters are powered from the DC power system and supply 115-volt AC to various airplane systems and navigation equipment
What type of power do the alternators provide?
208-volt, 7.4 KVA, variable frequency (“frequency wild”), three-phase power
What do each of the two engine-driven alternators supply power to?
The windshield, side screen and stall vane heating
What power are the emergency power packs rated at?
24 VDC, 4-amp-hour
What due BATT1 and BATT2 supply in the event all generator power fails?
Maintain DC power to the PE bus bar.
What are the three positions of the BATT switch?
ON/OFF/EMERG
When generators are off, what does setting the BATT switch to ON do?
Uses No. 1 battery to close emergency contacts Nos. 1 and 2 which connect No.1 and No. 2 battery to operate in parallel to energize PE bus bar via diodes.
When are bus bars PS1 and PS2 energized?
When a generator or external power is on line
What happens to the batteries when a generator comes on line?
Both emergency contactors remain closed, and a battery s connected to the bus bar via closure of the appropriate battery contact. When the buses are tied, both battery contactors are closed to connect No. 1 and No. 2 batteries to the PS bus bars for battery charging.
What is required to recharge the batteries?
A generator must be online and the buses must be tied.
What bus bar recharges the batteries
The PS bus bars
What does setting the BATT switch to EMERG do?
Closes both emergency contactors via individual circuits to connect No. 1 1 and No. 2 batteries to the PE bus bar. EMERG also causes the battery contactors to open, thereby disconnecting the batteries from their charging circuit.
When the batteries are fully charged and correct EP is carried out, No, 1 and No, 2 batteries are guaranteed to maintain essential services for a minimum of how long?
30 minutes.
What does setting the BATT ISOLATE switch to BATT 1 or BATT 2 do?
Opens the associated battery contractor, isolating the battery from the main bus bar.
Setting the BATT ISOLATE switch to NORM does what?
Permits BATT 1 and 2 battery contactors to close when the bus bars are powered from the airplane generators or when charging NO. 1 and NO.2 batteries from an external power supply.
CAUTION: No. 1 Battery may be excessively discharged and damaged how? Why?
If the roof switch on panel DA and the entry light switch on the forward cabin bulkhead are left ON for long periods while external power is applied.
This is because the vestibule roof light and the entry light are connected via their switches directly to the No 1 battery.
What does the START PWR switch do?
Functions as a start master switch for either external or internal starts. Starting is now available via START ENG 1 or ENG 2 switch
For an internal start, what does the START PWR switch energize?
Energizes an internal start contactor to connect No 1 and No 2 batteries to a start bus bar. Bus bar PE remains energized with the BATT switch on to supply essential services such as fire protection during engine starting.
When is battery charging accomplished
When the BUS TIE is closed and a generator is on line.
Or:
With an external power supply connected and the EXT PWR switch on, turn the EXT PWR CHG switch to ON
When should the EXT BATT CHG switch be turned off?
When the rate of charge is less the 5 amps.
Can you start the engines when the EXT BATT CHG switch is set to ON?
No.
How are the engine generators cooled?
By an air intake in the engine cowling. Ground cooling is provided by integral fan.
How is engine generator output stabilized?
By an associated Generator Control Unit (GCU)
NOTE: What can cause the tripping of the generator field circuit? When does this happen?
Overvoltage and overexcitation or opening the generator line contactor (GLC).
The opening of the field cirri occurs upon detection of these faults whether or not the GLC is closed.
What does GLC stand for?
Generator Line Contactor
Any fault detection and opening of the GLC does what?
Takes the generator off line and light the GEN FAIL and MWS ELECT annunciators
When a GLC is opening and the generator is taken off line, how can an attempt to reinstate be made?
Hold the associated GEN CLOSE/TRIP switch to CLOSE for five seconds and then release
NOTE: With external power on the aircraft, can closure of the GLC be accomplished?
No, closure of the GLC is inhibited.
What is the purpose of the Bus-tie contactor?
Splits the main bus bars in the event of power supply failure or malfunction
How is the bus-tie contactor manually controlled?
Via a spring-loaded BUS TIE CLOSE/OPEN switch
How it the bus-tie contactor automatically opened?
By the voltage-sensing unit in overvoltage or undervoltage conditions
What happens when the bus-tie contactor open?
Bus bars PS1 and 2 are split, and the generator-equalizing circuit is open
What does the equalizing circuit do?
Ensures equal load sharing between generators when the systems are paralleled and serviceable.
What are the limits that cause the voltage-sensing unit to close the bus-tie contactor?
- 5 +- 0.5 volts
24. 5 +- 0.5 volts
What prevents the voltage-sensing unit from closing due to transients?
Time delay circuits
How do you manually turn off an unserviceable channel when the PS1 and 2 bus bars are split?
By positioning the associated generator control switch to TRIP
How do you automatically turn off an unserviceable channel when the PS1 and 2 bus bars are split?
By the operation of the GCU overvoltage or reverse-current protection devices
How is overvoltage protection provided
The GCU overvoltage protection device opens the generator field circuit when the generator terminal voltage is 32.5 volts or above. The GLC is signaled to disconnect the generator from the associated bus bar PS1 or 2.
What can the generator control switches be used for?
To reinstate an off line generator or take a malfunctioning generator off line
How do you open the GLC and generator field circuit?
Momentarily position the GEN switch to TRIP
How do you reinstate a generator?
Hold the GEN switch to CLOSE for five seconds. Generator comes on line when the switch is released provided no fault exists.
How is the ground supply contactor controlled and to what systems does it supply power?
Controlled via the EXT PWR ON/OFF switch.
Powers the bus-bar system and the starter supply lines
NOTE: With the BATT switch ON and ground power plugged in, selecting START PWR on first has what effect?
Causes the EXT PWR switch to become ineffective.
What feature must a ground power unit have IOT to supply power to the aircraft?
A current limiter for 1,100 amps
What provides power for the windshield and side windows?
Two wild-frequency alternators
What type of power do the inverters provide?
Single-phase, 115-volt, 400Hz
Where are the inverters located?
Rear equipment bay
What systems do the inverters power under normal operation
Inverter 1 supplies XS1
Inverter 2 supplies XS2
Can one inverter feed all distribution lines?
Yes
If an inverter fails, what happens?
Changeover is achieved automatically
What are the positions of each INV switch?
START, STOP, and normal operation (not labeled)
What does pushing each INV switch to START do?
Energizes the associated contactor and a relay to start the selected inverter and connects the output to the respective XS distribution line
Two unswitched transformers provide power certain navigation equipment. What are the two types of power?
6- and 26-VAC
The No. 1 inverter receives power from what bus bar?
PS1 bus bar
The No. 2 inverter receives power from what bus bar?
PS2 bus bar
The No. 2 26-VAC transformer receives power from what source?
XS1 line
Describe BATT 6
24 VDC, 4-amp-hour sealed lead acid battery located in the avionics shelf of the aft cabin
What systems are powered by BATT 6?
SELCAL, data concentrator, and file server
What does BATT 3 do?
Provides secondary power to ADC-1, AHRS-1, AVN AUX LH, CDU-1 and MFD-1
What does BATT 4 do?
Provides secondary power to ADC-2, AHRS-2, AVN AUX RH
What does BATT 5 do?
Powers several internal and external lights around the emergency escape hatch
What does BATT 6 do?
Provides limited time power source to the Emergency Standby Instrumentation System (ESIS)
How is the Radio Emergency System activated
By a switch on the DA panel behind the copilot
What batteries supply power to the radio emergency system?
BATTs 3 and 4
What systems are powered by the Radio Emergency System?
AHRS-1, ADC-1, Pilot MFD, CDU-1, CRL-23 tuner, VHF NAV 1, VHF COMM 1, Pilot and Copilot audio panel
NOTE: Where is audio available from when using the Radio Emergency System?
Via headset only
What is the min battery voltage?
23 volts
What is the max battery charge rate prior to takeoff?
20 amps
What is the generator amp limit?
300 amps
Where is the ground power receptacle?
On the right rear fuselage
What ground power is required for an external start?
28VDC with a min output of 42kW (short-term capability of 28 volts and 1500 amps) and fitted with a 1,100 amp limiter
What type of external power is acceptable for ground testing aircraft electrical systems?
a 28 VDC battery trolley
END CHAP QUESTION 1 - The batteries will maintain essential service during a full generator failure for:
30 minutes
END CHAP QUESTION 2 - The max battery amps for takeoff is:
20 amps
END CHAP QUESTION 3 - When a generator is off the line and GEN FAIL and ELECT annunciators are illuminated, the generator can be reinstated by:
Position the GEN switch to CLOSE for 5 seconds then release
END CHAP QUESTION 4 - The battery charging rate can be monitored by:
Depressing the BATT button on the ammeters
END CHAP QUESTION 5 - The ground power receptacle is located:
On the right rear fuselage
END CHAP QUESTION 6 - For engine starting, the ground power unit must produce:
28 VDC and 1,500 amps
END CHAP QUESTION 7 - CBs protecting unswitched PE circuits are marked to ease isolation in the event of smoke or fire with:
A white background
