Electrical Flashcards
What type of power to most of our generators produce
AC
What type of power does the aircraft use
115VAC and 28VDC electrical power
What’s our primary source of electrical power
- AC electrical power
- supplied by 2 engine driven integrated drive generators
What’s a transformer rectifier unit (TRU) do?
Converts 115VAC to 28VDC power
What does the AC power center (ACPC) do?
Distributes power to all AC buses during normal operations
What’s an IDG?
It’s an “integrated drive generator. It consists of a constant speed drive and a generator. It’s the aircrafts primary source of AC power.
What are our alternate electrical sources
The Auxiliary Power unit (APU) and Air Driven Generator (ADG)
GCU fault protection
- Over/under voltage
- over under frequency
- generator phase sequence…
Electricity generation altitude limitations
Engine IDG’s = 41,000
APU. = 41,000
ADG…
Integrated drive generators
- Consists of a generator and a constant speed drive
- Constant speed drive takes variable N2 and produces a constant 12,000RPM generator speed. This creates a consistent electrical output.
When will the IDG FAULT switch light illuminate?
The IDG FAULT switch light illuminates on the overhead panel when there’s either high IDG oil temperature or low IDG oil pressure.
QRH checklist types
Command, response type
What’s the correct response to a request to confirm something with the other pilot?
Either “I agree” or “no’”
What happens when you hit the IDG fault switch on the overhead panel
The disconnect solenoid moves, which allows the disconnect plunger to engage the IDG worm shaft and disconnects the IDG by spreading the jaw tooth clutch.
IDG critical temperatures
At 168ºC IDG oil temp, the fault light will come on
At 186ºC the hot IDG oil will melt the disconnect solenoid sauter point and disconnected the IDG automatically
What are the different AC buses?
Bus1
Bus2
Ess bus
Serv Bus
AC BUS 1 power priority
- 1st from IDG 1
- 2nd priority is to get electricity from APU generator
- 3rd priority is IDG 2
- 4th priority is external ground power
What’s the ground power priority?
Lowest power priority. You have to turn off APU and engine to get ground power to work.
AC BUS 2 power priority
1st is IDG 2
2nd is APU generator
3rd is IDG 1
4th is External power
AC Essential bus power and faults
- Gets is power from AC BUS 1, and therefore its generally powered by IDG 1.
- If the AC BUS 1 loses power, AC BUS 2 will automatically power the AC ESS BUS
- The AC ESS XFR switch light illuminates any time the AC BUS 1 has failed and is being powered by AC BUS 2. If it doesn’t automatically switch to being powered by by AC BUS 2, pressing the switch light will manually switch to AC BUS 2
AUTO XFER inhibit switch light
- FAIL: illuminates when a bus fault or generator overcurrent is detected by the GCU. The affected generator is taken offline. The GCU automatically inhibits the auto transfer system on the affected side.
- Pressing the switch light turns off the Bus 1/2 respectively. Hitting it again turns the bus back on.
AC external power switch light
- AVAIL means the ground power is connected and is the correct voltage, frequency, and phase
- IN USE means that the aircraft systems are being actually power by ground power
Ground power control panel and plug in location
… I’ll get back to it…
AC external service switch
-Looks like the internal switch light. Pressing the external switchlight only powers the SERV bus.
Air driven generator
-Automatically deploys when AC Bus 1 and bus 2 to fail simultaneously.
-Can
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ADG powers which things
- AC essential bus
- Slats and flaps (operated at half speed)
- Stab trim channel 2
- Hydraulic 3B
Will hydraulic 3B run in the off position when the ADG is running?
Yes. When the ADG is running, the ADG
What happens if the ADG is running and youre able to restablish alternate power.
The essential bus will remain powered by the ADG until you push the “PWR TXFR OVERRIDE” and then the AC1/2 will power the essential bus
ADG speed
- Between 155-160kias start load shedding with the essential DC bus
- Need to configure for landing no slower than 140kias
What are our DC power sources?
4 Transformer rectifier units (TRU’s) and 2 batteries (main battery and APU battery)
What charges the batteries?
Main battery is powered by AC Bus1
APU battery is charged by the AC service bus
Battery charging is controlled automatically
How many TRU’s do we have and where are they located?
4, all in the nose compartment.
How many DC buses do we have?
9
What are the DC buses?
DC Bus1 DC Bus2 DC SERV bus DC UTIL bus DC ESS bus DC BATT bus DC APU BATT DIR bus DC MAIN BATT DIR bus DC EMER bus (not normally shown)
What is the max TRU load
-All 4 are rated at 120AMPS
What are the 4 TRU’s
TRU1, TRU2, ESS TRU1, and ESS TRU2
How many DC Tie contactors are there? What are there names?
5 DC tie contactors exist
- MAIN TIE
- CROSS TIE
- ESS TIE
- DC ESS TRU 2 transfer contactor
- Service BUS contactor
Can we control the TIE’s?
Negative. It’s all automatic.
What closes and opens the ties?
The DCPC’s (DC power center’s)
What is the most common DC bus to lose when a TRU fails?
The UTIL bus
What does the battery master switch do?
Allows the batteries to power the DC BATTERY BUS via both APU BATT DIR BUS and MAIN BATT DIR BUS
Which busses are hot
- APU BATT DIR BUS
- MAIN BATT DIR BUS
- DC EMER BUS
Max permissible time for ground operations with battery power only
5 minutes, the fans that cool the EICAS CRT screens are AC powered so without turning on the APU, engines, or applying ground power, the EICAS screens could overheat
Where is the external AC power receptacle located?
Lower, right side, forward of the nose area
What is the AC electrical system rated at?
115VAC, 400HZ, 3 phase
What is the voltage of the DC electrical system?
28 volts
Max engine generator (IDG) load
40KVA to 41,000
How many circuit breaker panel are there? Where are they located?
There are 4 circuit breaker panels. 2 are found in the cockpit, 1 in the aft equipment bay, and 1 in the forward, unpressurized nose compartment.
Which TRU does AC BUS 1 power?
TRU 1
Which TRU(s) does AC BUS 2 power?
TRU 2 and ESS TRU 2
Which TRU does AC ESS BUS power?
ESS TRU 1
If TRU 1 fails which TIE contactor is likely to open? Which DC buses will likely be lost?
The main tie contactor will likely open. This will likely lead to the loss of the UTIL BUS as all the TRU 1 and TRU 2 items will attempt to be powered by TRU 2 which would exceed 120AMPS
What will happen if TRU 1 and TRU 2 fail?
The MAIN TIE and CROSS TIE will automatically close. The ESS BUS 2 TRU will then powers DC BUS1 and 2, as well at the SERV BUS. The UTIL bus is load shed.
What will happen if ESS TRU 1 fails?
The ESS TIE bus will automatically close, allowing ESS TRU 2 to power the DC ESS BUS
What items are normally powered by TRU 1?
DC BUS 1
What items are normally powered by TRU 2?
DC BUS 2
DC SERV BUS
UTIL BUS
What is normally powered by ESS TRU 2?
The DC BATT BUS
What is normally powered by ESS TRU 1?
The DC ESS BUS
What does the ADG power?
It powers only the AC ESS BUS, which in turn powers ESS TRU 1, which powers the DC ESS BUS. Additionally the ESS TIE would automatically close so the ADG could also power the BATT BUS.
In short it powers…
- DC ESS BUS
- HYD pump 3B
- Slats/flaps (half speed)
- STAB TRIM CH2
What would happen if the ADG was our only source of power and ESS TRU 1 had failed?
The ESS TRU 2 transfer contactor would close which would allow the ADG to power ESS TRU 2 instead of ESS TRU 1. The ESS TIE would close and allow ESS TRU 2 to power both the DC ESS BUS and the DC BATT BUS.
What would happen if TRU1 failed and AC BUS 2 fails?
ESS TRU 2 transfer contactor would close allowing the AC ESS BUS to power ESS TRU 2. In turn ESS TRU 2 would power DC BUS 1, DC BUS 2, and SERV BUS through the closed MAIN TIE and CROSS TIE. The UTIL bus would be load shed.
What’s powered by DC BUS 2?
Powers the NAV lights and provides cabin lighting and limited power for cleaners.
Can the DC SERVICE BUS be powered without AC power?
Yes. It can be powered by the APU BATTERY DIRECT BUS (and hence the batteries) by selecting the DC SERVICE switch on, located on the overhead panel. This is NOT a procedure we follow at Mesa Airlines!!!
Which switches are selected to OFF during the terminating checklist?
All of them
What does turning the battery master switch to ON do?
Supplies battery power to the DC BATT BUS
What would happen in flight if all generators and ADG fail?
The ESS TIE would close and the DC BATT BUS and DC ESS BUS would be powered by the APU and Main battery. This should provide approximately 30 minutes of DC power. Then on touchdown, weight on wheels will remove battery power from the DC ESS BUS unless the ADG handle is deployed.
What’s the main battery voltage and capacity?
24 volts and 17 amp-hours
Where’s the main battery located?
In the nose compartment
What’s the APU battery voltages and capacity?
24 volts and 43 amp-hours
Where’s the APU battery located?
In the aft equipment bay
What type of battery are the Main and APU batteries?
Nickle-cadmium batteries
What’s a TRU?
Transformer Rectifier Unit
What’s a GCU?
Generator Control Unit
How many GCU’s do we have?
3
What do the GCU’s do?
They control and monitor the generators and provide protection and voltage regulation of each
What will the GCU remove generator output for?
4 things
- under/over voltage
- over/under frequency
- generator or bus overcurrent
- generator phase sequence
Where are the GCU’s located?
They are located in the avionics compartment
What are the different GCU’s we have?
GCU1, 2, and 3
What does GCU 1 control?
Controls IDG1 and the distribution of AC power to AC BUS 1
What does GCU 2 control?
Controls IDG 2 and the distribution of AC power to AC BUS 2
What does GCU 3 control?
The APU generator logic
What’s the IDG rated power?
40KVA all the way to FL410
How many IDG’s does the aircraft have?
- One on each engine.
What’s the purpose of the constant speed drive portion of the IDG?
It takes the variable N2 speed, and converts it to constant 12,000RPM generator speed. This allows a steady power generation.
Does the APU have an IDG?
No. The APU runs at a constant RPM so no IDG is needed.
IDG shear point. Will automatically shear and disconnect the IDG in an over-torque situation.
What’s number 1?
1.) Output shaft to the variable drive unit
what’s number 2?
2.) Worm shaft
What’s number 3?
3.) Disconnect plunger. The engages the worm shaft which will unscrew itself. This will in turn disconnect the clutch to the constant speed drive from the accessory gearbox input, and cease electrical production.
Whats number 4?
4.) disconnect solenoid. This is energized when you hit the IDG FAULT/DISC switchlight. When energized it allows the spring loaded disconnect plunger to engage the worm drive.
What’s number 5?
5.) Input from the engine accessory gearbox
What’s number 6?
6.) Shear point. Will automatically, physically disconnect the accessory gearbox from the worm drive during an over torque event.
What’s number 7?
7.) Jaw tooth clutch separation point. This is where the worm drive would be disconnected from the accessory gearbox if the the disconnect plunger engages the worm drive.
What’s number 8?
8.) Reset ring. Allows the disconnect plunger to be put back in its normal position. Can’t be done in flight.
Where does the AC ESSENTIAL BUS normally get its power?
The AC ESS BUS is normally powered by AC BUS 1.
What does the AC ESS XFER switchlight button do?
It switches the essential bus feed from AC BUS1 to AC BUS 2 and vice versa.
What does it mean if ALTN (white) is illuminated on the AC ESS XFER button?
It indicates that the AC ESS BUS is being powered from AC BUS 2.
What happens to the AC ESS BUS when IDG 1 fails?
It automatically switches to receiving power from AC BUS 2. If this fails to occur it can be manually switched by depressing the AC ESS XFER button on the overhead panel.
When would the AUTO XFER switchlight be illuminated with a yellow FAIL?
FAIL is illuminated when the GCU detects a BUS fault or IDG overcurrent. When this happens the generator is taken offline and the GCU automatically inhibits the auto transfer system on the affected side.
What’s the AC auto transfer system?
It’s a system that automatically allows any non emergency power source (IDG1, IDG2, APU, External power) to power all aircraft systems by correctly routing the power.
What does the AC auto transfer system do when IDG1 fails?
It will automatically power AC BUS 1 using power from IDG 2. This can be inhibited if automatically if a bus fault or IDG overcurrent is detected.
Is the DC EMER BUS normally displayed on the EICAS ELEC page?
No. It is only displayed when 1 or more of its power sources is lost.
What does the DC EMERGENCY BUS power?
- Hydraulic shut off valves (SOV’s)
- Fuel SOV’s
- Bleed air SOV’s
- Fire bottle squibs
What does the APU BATTERY DIRECT BUS power?
- APU starter
- refuel/defuel panels
- refuel/defuel valves
What powers the APU engine control unit (ECU)?
DC BATTERY BUS
When does the ADG automatically deploy?
When AC BUS 1 and 2 lose power.
How can you manually deploy the ADG?
By pulling the manual ADG deploy handle
Both IDG’s fail in flight and the ADG’s deploys to power critical systems. Later in the flight you are able to get one of the main generators working again. Will the generator automatically start powering the systems? Will the ADG retract?
The generator will NOT automatically begin powering systems. To do that you’d have to hit the PWR TXFR OVERRIDE button to switch to generator power. That ADG will remain deployed.
When will the AVAIL light illuminate on the AC switchlight?
When ground power is connected and is the correct voltage, frequency, and phase.
