Electrical

Question 1

What powers the ARCDUs?

Answer 1

Each ARCDU is powered by the offside Main Bus and onside Essential Bus.

Question 2

Describe the batteries on the Q400.

Answer 2

Three 24 volt, 40 amp hour batteries located in the nose.
Main (Lower bay, Forward) -
Aux (Lower bay, Aft) -
Standby (Upper bay) -

Question 3

Describe the generators on the Q400

Answer 3

Two Air-cooled, 28 volt, 400 amp DC starter/generators mounted on the engine accessory gearbox.

Two oil-cooled, 115 volt three-phase, variable frequency AC generators mounted on the propeller reduction gearbox.

One air-cooled, 28 volt, 400 amp DC starter/generator on the APU for ground use only.

Question 4

Are there any other sources of DC power?

Answer 4

Two 28 volt, 300 amp Transformer Rectifier Units (TRU) mounted in the upper right part of the nose which convert 115 volt AC to 28 volt DC. They are connected to the secondary buses.

Question 5

How many DC buses does the aircraft have?

Answer 5

7

Battery
Left and Right Essential
Left and Right Main
Left and Right Secondary

Question 6

What unit controls the bus system and what is it’s primary function?

Answer 6

The Electrical Power Control Unit (EPCU) can automatically reconfigure the bus ties to respond to electrical failures.

Question 7

What buses can the AC system power and what can it not power?

Answer 7

The AC system, including AC external power, can provide power to all buses but is not available to assist in engine start.

Question 8

During engine start which battery is unavailable to assist in the start?

Answer 8

The Standby battery

Question 9

What buses are are the batteries connected to and what switches control these connections?

Answer 9

The Main Battery is connected to the Right Essential bus by the BATTERY MASTER switch and the Right Main Bus by the MAIN BATT switch.

The Aux Battery is connected to the Left Essential Bus by the BATTERY MASTER Switch and the Left Main Bus by the AUX BATT switch.

The Standby Battery is connected to the Right Essential Bus by the BATTERY MASTER switch and the Left Main (for charging only) by the STBY BATT switch.

Question 10

How long will the batteries last in flight as emergency back-up power?

Answer 10

Approximately 45 minutes.

Question 11

What indication will we have if the EPCU automatically disconnects a battery from it’s associated Main Bus due to a malfunction?

Answer 11

An amber MAIN BATTERY, AUX BATTERY or STBY BATTERY CWP light and the MASTER CAUTION.

Question 12

What buses receive DC External power?

Answer 12

The Left Main Bus is connected to the external power and the EPCU automatically closes bus ties to allow all 6 buses to receive DC power.

Question 13

With the DC external power connected what power sources are inhibited?

Answer 13

The engine and APU generators are inhibited.

Question 14

When will the EPCU automatically disconnect the external power?

Answer 14

Below 22 volts or above 31 volts.

Question 15

What is a GCU and what does it provide?

Answer 15

The Generator Control Units switch the starter/generators from the starter mode to the generator mode at 50% NH. They also ensure that the generator supplies a constant 28.5 volts to its associated Main Bus.

Question 16

What bus receives power from the APU generator?

Answer 16

The Right Main Bus.

Question 17

How many DC power sources can fail before the EPCU will automatically load shed DC buses?

Answer 17

Two, if more than two fail the EPCU will leave some DC buses un-powered.

Question 18

In the event of both TRUs failing and one DC generator failing what happens?

Answer 18

If both TRUs and one DC generator fail the EPCU will power the Main buses via closing the Main Bus Tie but will de-power the secondary buses.

Question 19

Explain what happens with a Main Bus Fault.

Answer 19

When the EPCU detects a potential Main Bus fault it inhibits the closing of the Main Bus Tie or the Main-Secondary Bus Ties. A DC BUS CWP light will illuminate and the QRH will instruct the crew to cycle the BUS FAULT RESET Switch.

After approximately 5 seconds if the EPCU determines there is a bus fault it will disconnect the DC GEN and batteries from the faulty bus leaving it un-powered and isolated.

Question 20

What is powered by the AC system?

Answer 20

De-icing/Anti-icing heaters
Standby Hydraulic Pump
TRUs
Auxiliary Fuel Pumps
Galley loads

Question 21

If an AC generator fails how is the AC system powered?

Answer 21

In the event of an AC generator an automatic cross-tie will close to provide power to both AC buses.

Question 22

Describe how an AC bus fault is dealt with.

Answer 22

If an AC bus fault is detected the EPCU isolates that bus but the AC GEN will stay online and due to the cross-tie is available to power the opposite bus in case of an additional AC GEN failure.

Question 23

How many buses can a single AC GEN power?

Answer 23

A single AC GEN can power the entire AC and DC electrical systems if both TRUs remain functional.

Question 24

What will happen when both DC GENs fail and one TRU fails?

Answer 24

If both DC generators fail and one TRU does the EPCU enters emergency mode and will disconnect the batteries from the Main buses leaving only the Essential and Secondary buses power. The Essential buses will only be power for approximately 45 minutes. For an attempted air-start the EPCU will reconnect the batteries to the main buses only for the duration of the start attempt.

Question 25

Explains what happens with a Secondary Bus fault.

Answer 25

A Secondary Bus fault will trip the TRU circuit breaker, the EPCU will close the Secondary Bus tie and due to the short circuit will blow the Secondary Bus cross-tie fuse to blow. This will isolate the faulty Secondary Bus.

Question 26

What items are on the Hot Battery Bus?

Answer 26

Refuel Panel
Flight Deck Dome light
Clocks
Fuel and Hyd SOVs
Boarding lights
PA Emer Power

FIRE EXT/CONT AMP
FUEL & FMU
APU/CARGO MAN EXT