Oral Prep - Electrical

Question 1

What are the primary sources of AC power?

Answer 1

Two engine and one APU driven generators

Question 2

What is the normal source of DC power?

Answer 2

Five Transformer Rectifier Units (TRUs).

Question 3

How many batteries are installed and where are they located?

Answer 3

Two nicad batteries located in the aft equipment bay.

Question 4

One battery is referred to as the __?__ battery and the other is the ? battery. Which is bigger?

Answer 4

The MAIN battery is rated at 24 volt 17 amp/hr, with a larger 24 volt 43 amp/hr APU battery.

Question 5

What is continuously powered by both batteries?

Answer 5

The batteries provide constant power to the MAIN and APU BATT DIR BUS, and are capable of powering the DC BATT BUS and DC EMER BUS when needed. The DC EMER BUS provides power to the engine and APU extinguishers and shut-off valves. The bus is connected directly to the APU BATT DIR BUS and the BATT BUS and is continuously powered. The DC EMER BUS is only displayed on the DC synoptic page when it is faulted or not powered.

Question 6

What role do the batteries play in a total AC power failure?

Answer 6

Provide an emergency DC power supply in-flight should all AC power be lost and the ADG fail, thus powering the DC ESS bus (captains instruments) and the BATT Bus (EICAS).

Question 7

Can you discharge an engine or APU fire bottle in a cold, dark airplane?

Answer 7

Yes

Question 8

What are the individual components that make up an IDG (integrated drive generator)?

Answer 8

A 30-kVA AC generator and a constant speed drive.

Question 9

Under what conditions should an IDG automatically disconnect from the engine?

Answer 9

If an overtemperature or overtorque condition occurs.

Question 10

Under what conditions will a GCU remove itself from the bus system?

Answer 10

Over or under voltage, over or under frequency or generator or bus overcurrent

Question 11

How can an IDG be manually disconnected from its engine?

Answer 11

By pressing the IDG DISC switch on the Electrical Services Panel.

Question 12

Once disconnected, can the IDG be reconnected in flight?

Answer 12

No

Question 13

What does a green AVAIL light illuminated on the AC External switchlight indicate?

Answer 13

Power is connected and is of correct phase, voltage, and frequency.

Question 14

What is the function of the AC ESS XFER switchlight?

Answer 14

To manually transfer, or indicate automatic transfer of the AC ESS Bus to AC Bus 2.

Question 15

When will power to the AC Essential Bus automatically switch from AC Bus 1 to AC Bus 2?

Answer 15

When AC Bus 1 is not powered.

Question 16

Is it normal for the AC Essential Bus switch/light to be illuminated while on battery power only, such as when at the gate prior to APU start?

Answer 16

Yes, the bus logic is working correctly, but because there is no AC power on AC Bus 1, the bus attempts to transfer to the alternate.

Question 17

In the above scenario is the AC Essential Bus being powered?

Answer 17

No

Question 18

What does the FAIL light illuminated in an AUTO XFER switchlight along with the amber EICAS message AUTO XFER FAIL indicate?

Answer 18

A bus fault or generator overcurrent condition.

Question 19

What is power source priority for AC Bus 1, AC Bus 2?

Answer 19

AC Bus 1 - IDG 1, APU, IDG 2, External Power
AC Bus 2 - IDG 2, APU, IDG 1, External Power

Question 20

What effect will an IDG disconnect, auto or manual, have on the Hydraulic system?

Answer 20

The cross side Hydraulic ACMP (AC Motor Pumps) will be load shed.

Question 21

What does illumination of the amber FAIL lamp in the AUTO XFER switchlight indicate? Is this switchlight manual or automatic? What is the function of this switch, what does it do?

Answer 21

In the event of a BUS FAULT or GENERATOR OVERCURRENT condition, the GCU can inhibit the normal bus transfer logic. Normal bus priority logic allows for automatic bus transferring when the normal power generation source is changed or interrupted. When the GCU senses a FAULT condition in its associated main AC bus, the GCU will generate an AC 1(2) AUTO XFER caution message. Although the generator may still remain operating and the bus powered, the AUTO XFER FAIL will prohibit the normal automatic bus transfer. This prevents a potentially shorted bus from overloading its on-side generator, then transferring to another generator. Normally automatic, AUTO XFER can be manually inhibited using the push-button switchlight on the overhead panel. Inhibiting an automatic transfer allows for bus isolation.

Question 22

How can AUTO XFER be manually inhibited?

Answer 22

By pushing the AUTO XFER switchlight on the electrical services panel

Question 23

Which DC BUS TIE will not operate automatically?

Answer 23

DC ESS TIE.

Question 24

What does a white closed light illuminated on the DC BUS TIE 1 or 2 switchlights indicate?

Answer 24

The corresponding DC Bus has been automatically tied to the Service TRU or another available source.

Question 25

What is the Tri State policy on crewmembers resetting cockpit electrical Circuit Breakers in flight ?

Answer 25

A circuit breaker must not be reset or cycled (i.e., opened or closed) unless doing so is consistent with explicit procedures specified in the OM/QRH or unless, in the judgment of the PIC that resetting or cycling of the circuit breaker is necessary for the safe completion of the flight.

Question 26

What is the function of the DC SERVICE switch?

Answer 26

It controls power to the DC Service Bus.

Question 27

If AC external power is to be utilized, explain how AC power is properly established?

Answer 27

If the green AVAIL light is illuminated, press the external AC switchlight to supply the electrical system.

Question 28

What is an IDG?

Answer 28

Two IDGs supply 115 volt, 400 Hz electrical power to six AC buses.

Question 29

When will the ADG automatically deploy?

Answer 29

During a complete AC power failure.

Question 30

What is the function of the PWR TXFER OVERRIDE switch on the ADG Panel?

Answer 30

When pressed it de-energizes the AC Emergency, DC Emergency and 3B hydraulic contactors if normal AC power is restored after ADG deployment.

Question 31

What are an IDGs two primary components?

Answer 31

The IDGs consist of two components: a CSD and an electrical generator.

Question 32

What does the illumination of the FAULT lamp in the IDG switchlight with an IDG caution message on EICAS indicate?

Answer 32

HOTLOP: CSD oil is cooled by an air/oil heat exchanger in each engine pylon. If IDG oil overheats or oil pressure
drops below limits, the IDG switchlight FAULT lamp illuminates on the overhead panel along with an EICAS IDG caution message.

Question 33

What is the function of the CSD?

Answer 33

The generators must turn at a constant RPM to produce a constant 400 Hz. The CSD performs like an automatic transmission, using its own integral oil system to change variable engine speed to a constant generator RPM.

Question 34

How can an IDG be disconnected from the accessory gearbox?

Answer 34

The IDG can automatically or manually be disconnected from the accessory gearbox.

Question 35

What will cause an IDG to automatically disconnect? How does this physically happen?

Answer 35

Should the manual disconnect fail, an automatic disconnect of the IDG will occur when the CSD internal temperature exceeds a certain limit (melting a fusible plug), or by shearing the IDG drive shaft when an overtorque condition occurs.

Question 36

How do you manually disconnect the IDG?

Answer 36

Pressing the IDG DISC switchlight on the overhead panel energizes an electrical solenoid that causes the drive gear to retract from the engine accessory gearbox. Once disconnected, the IDG can only be reset on the ground.