Electrical System Flashcards
(T) How does the IDG operate when set in the “Auto” position?
It connects the IDG to the respective AC bus automatically according to system logic. ( IDG 1 - AC BUS 1/ IDG 2 - AC BUS 2)
(I) What happens when you turn the IDG switch to the OFF position?
You are simply opening the contactor between the IDG and the respective AC bus, subsequently isolating it from the respective AC bus.
(I) When would you ever turn the IDG switch to the DISC position?
How does this affect the IDG in question?
Only when the QRH instructs you to! See “IDG OIL 1 (2)” caution in the QRH for an example.
When you turn the switch to DISC (Disconnect), the IDG will mechanically disconnect, making it impossible to reconnect it in flight.
(B) You notice that the Amber led next to the IDG switch is illuminating. What does that mean? What if you don’t do anything about it?
The Amber led light indicates which IDG to disconnect.
It is associated with the IDG OIL 1(2) caution message (IDG is subject to excessive oil temp/low oil pressure).
If nothing is done in response to the indication, the IDG will shear off due to torque as a result of the increased temperature of the unit.
(B) How many IDG’s are equipped?
2
(T) Unlike the engines, the APU does not have a GCU. Why?
The APU is designed to operate at constant speed. Therefore, there’s no need for a GCU.
(B) If you activate the APU, when can you expect to receive electrical power from it?
@ 95% + 3 seconds
(O) You are in flight. Both engines and your APU are operating. You are receiving AC power from both IDGs and the the APU generator. Suddenly, IDG1 fails/disconnects. What is now powering AC BUS 1?
The APU generator is powering BUS 1 due to automatic system logic.
Onside
Inside
Outside
Cross-side
(T) What bus is the DC ESSENTIAL BUS normally powered by?
AC BUS 2
(I) What is the function of bus ties when set to the auto position?
The bus ties close and tie the two networks together automatically, would there be a failure in the electrical system in order to power all buses around the failed bus/component.
(B) What is a TRU? How many TRU’s are incorporated in the electrical system?
Transformer Rectifier Unit - converts 115 V AC to 28 V DC.
There are 3 TRUs in the system.
(O) What is an inverter? What is the purpose of the inverter?
An inverter converts 28VDC to 115VAC.
The purpose of the inverter is to provide AC power to the AC STBY BUS when the airplane is only being powered by the Batteries.
(O) What’s on the AC STBY bus?
Engine 1 - Exciter 1A
Engine 2 - Exciter 2A
(O) DC BUS 2 is normally powered by TRU 2. If TRU 2 is disconnected or if it fails, will DC BUS 2 still be powered? Rather than only answering yes or no, explain what will happen. Feel free to use the electrical diagram for this question.
Assuming that the bus ties are all in the AUTO position, it will still be powered.
DCTC will close, allowing electrical power to be transferred to DC BUS 2 through DC BUS 1.
(I) What is the minimum battery voltage required for normal operation according to the CFM?
21.0 V
(I) What is the normal activation sequence for the batteries? How about when you deactivate them?
Activation : BAT 1 first, then BAT 2
Deactivation: BAT 2 first, then BAT 1.
This is to minimize glitches that can occur in the system if done the other way.
(O) Explain what an IDG is and how it works
IDG - Internal Drive Generator is a CSD and an oil cooled generator inside the same case.
A CSD - Constant Speed Drive is a mechanical gearbox that takes an input shaft rotating at a wide range of speeds,(12,000RPM) delivering its power to an output shaft that rotates at a constant speed, allowing the IDG to operate at a constant speed.
(B) What battery voltage and temperature is required for an APU start using the batteries?
22.5 V
Battery temp > -20 DEG C
(O) Battery 1 and 2 have different selections in their 12 o clock position. Battery 1 - ON, Battery 2 - AUTO. Why is this?
The default position for BAT1 is ON, which simply powers DC ESSENTIAL BUS 1.
Additionally, Battery 1 provides FADEC and EICAS for a successful APU start to be carried out. Without FADEC, the APU simply won’t start and EICAS is needed to monitor the status of the APU RPM and Temperature in the APU EICAS indication field as well as any caution/warning messages.
Battery 2 normally powers DC ESSENTIAL BUS 2. The AUTO position simply ensures that battery 2 and it’s associated hot bus automatically segregates itself from the rest of the system and only powers the APU START BUS during an APU start.
(O) When an AC ground cart is hooked up to the airplane and running, you would expect to see the AVAIL light to illuminate. What does that light imply?
It implies that the ground cart is supplying AC electrical power @ 115 V, 400 HZ, 40 KVA and therefore available for use. If those values are off, the AVAIL light won’t illuminate.
(T) How long time does it take for the RAT to deploy? and how does it deploy?
- 8 seconds
- When AC Buses not powered in flight, deployment actuator relieves the system to open and fall down with gravity
(I) What important components are powered from the battery hot busses?
Battery 1 hot bus :
- Fuel SOV
- Hyd. SOV
- Fire extinguishers 1A and 2A
Battery hot bus 2:
- Fuel SOV
- Hyd. SOV
- Fire extinguishers 2A and 2B
(T) Is the inverter on only when used as an emergency back of all AC power supply?
No, it is always on anytime BATT 1 is ON
(I) Can you inadvertently deploy the RAT on the ground?
No, because of Weight-on-Wheels
