Electrical

Question 1

What buses are powered when the battery master is selected on?

Answer 1

• Left/right essential buses

- closes 3 contactors and connects the 3 batteries to the essiential DC buses.

Question 2

What buses are powered when the battery master and main BATT switches are selected on?

Answer 2

• Left/Right essential buses

- Right Main Bus

Question 3

What buses are powered when the battery master I MAIN BATT I AUX BATT I AND STBY BATT switches are selected on?

Answer 3

• Left/Right essential buses
• Right Main DC Bus
• Left Main DC Bus

Question 4

What buses are powered with the APU generator power?

Answer 4

• Left/Right Essential
• Left and Right Main
• Left and Right Secondary

Question 5

What buses are powered with DC external power?

Answer 5

• Left and Right Essential
• Left and Right Main
• Left and Right Secondary

Question 6

What buses are powered with AC external power?

Answer 6

• Left or Right AC bus

- Left or Right Galley bus

Question 7

What controls the 4 bus ties?

Answer 7

The Electrical Power Control Unit (EPCU)

Question 8

What is max DC generator load?

Answer 8

1.0

Question 9

What is the maximum battery load for take-off?

Answer 9

0.1

Question 10

What does a battery load indication of +1.05 indicate?

Answer 10

It indicates that the battery is in overcharge at 5% over the maximum rate of charge.

Question 11

What is the maximum output rating of the DC generators?

Answer 11

400 amps max

Question 12

What is the maximum output rating of the TRU’s?

Answer 12

300 amps max

Question 13

When does automatic load shedding of the galley buses occur?

Answer 13

If one of the AC Generators fail. The functioning generator will power both AC buses, but the load shedding relays will not allow power to the galley buses.

Question 14

When does emergency mode of operation occur?

Answer 14

The EPCU operates in emergency mode if:

• The airplane is in the air and
• Both DC generators are not available and
• At least one TRU is not available

Question 15

What will cause the EPCU react to a main bus fault?

Answer 15

• Transient nature of power or a voltage surge

Question 16

What does the EPCU do when it detects a main bus fault?

Answer 16

If the EPCU confirms an actual Main Bus Fault it will automatically take offline all of the DC components associated with the faulty bus (I.e., DC Starter-generator and batteries), leaving the faulty bus I powered and isolated. The QRH will instruct the crew to cycle the Bus Fault Reset switch in an attempt to reset the EPCU’s bus fault protection logic.

If a main bus fault occurs, the EPCU prevents main bus tie, and the main to secondary bus ties from closing, isolating the bus from other buses & power sources. The DC BUS caution light comes on to warn of the fault impeding condition.

• If the fault persists, after approximately 5 seconds, the EPCU sends a TRIP signal to the GCU, isolating the affected generator. The EPCU will also open and lock-out the contactors connecting the batteries to the affected main bus. The #1 DC GEN or #2DC GEN caution light comes on, and the MAIN BATTERY or AUX and STBY BATTERY caution light(s) come on. The EPCU continues to monitor the operating buses. All main DC services on the failed bus side will not operate.

Question 17

Will all buses be powered if a DC generator fails? How?

Answer 17

Yes, the left to right main bus tie closes and the other DC generator then powers both main feeder buses.

Question 18

Will all buses be powered if both DC generators fail? How?

Answer 18

Yes, both the Left and Right main to secondary bus ties close, and the TRU’s supply power to all the DC buses.

Question 19

Will all buses be powered if a TRU fails? How?

Answer 19

Yes, the left and right Secondary bus tie closes, and the other TRU then powers both secondary buses.

Question 20

Will all buses be powered if an AC generator fails?

Answer 20

No, the galley bus will not be powered.

Question 21

Which buses will be powered if both DC generators and one TRU fail?

Answer 21

This would be emergency mode;

• Left/Right Essential buses (by the batteries for approx 30 min only)
• Left/Right Secondary DC buses by the 1 remaining TRU

Note: Should an air start attempt be necessary while the EPCU is operating in the emergency mode, it will allow the batteries to be reconnected to the Main buses momentarily to assist in the start, but only for the duration of the start attempt.

Question 22

Which battery is the hot battery bus (battery power bus) connected to?

Answer 22

Standby Battery

Question 23

Can the EPCU disconnect the main bus tie if the main bus tie switch is on?

Answer 23

Yes, manual operation of the main bus tie through the MAIN BUS TIE switch is not possible once the EPCU has reacted to a fault.

Question 24

General electrical system of the Q400.

Answer 24

The DC power system is supplied by:

• 3 Ni-Cad batteries
• 2 engine driven starter/generators
• 2 transformer rectifier units (TRU’s)
• an optional Auxiliary Power Unit (APU)

The TRU’s supply 28 VDC and are powered by two engine driven 115 VAC generators.

There are both DC and AC external power receptacles for Ground power unit (GPU) connection.

Power is distributed by an electrical bus system. It re-configures for individual power source and bus failures, by automatically closing and opening bus tie contactors.

All AC and DC aircraft services can be powered from the AC generators or the AC external power alone.

Question 25

In flight, how long do the 3 batteries supply backup power to the aircraft essential services for?

Answer 25

Approx 30 minutes

Essential buses only, not the mains

Question 26

When does the EPCU incorporate external DC power protection from too high/ low supply of external DC power voltage?

Answer 26

When the voltage falls below 22+/- 1 or above 31+/-0.5