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)