Electrical System 2 (DC Power System)

Question 1

What is the purpose of a transformer rectifier unit (TRU)?

Answer 1

To transform AC power to DC power

Question 2

Where does the right TRU receive power from?

Answer 2

From the right generator and the AC bus contactor

same for left with the left generator

Question 3

Is one generator capable of supplying power to both TRUs in the event of a generator failure?

Answer 3

Yes, due to the crossover relay

Question 4

If one TRU fails, will the other TRU produce enough DC power to carry the entire electrical load?

Answer 4

Yes

Question 5

When either TRU falls below what voltages does a RECTIFIER FAILURE PFL and an AVIONICS advisory generate?

Answer 5

25.5 V for 2 seconds

Question 6

How many amps do the TRUs operate at?

Answer 6

50 Amps

Question 7

What is the voltage of the battery?

Answer 7

24 V lead acid battery

Question 8

The TRUs convert the AC power from the generator to what voltage of DC power?

Answer 8

28 V DC

Question 9

Why is there no interruption of power to the DC system if one TRU fails?

Answer 9

Due to the Diode Module. The Diode Module parallels the power output from both TRUs into a single output, so the DC busses are connected to the TRUs via a single diode, providing no interruption of power.

Question 10

How many DC Buses are there and what are they?

Answer 10

1. Left Essential DC bus
2. Right Essential DC bus
3. Nonessential DC bus
4. Battery Bus

Question 11

During normal operation with both generators online, what buses are active and powered by the TRU?

Answer 11

The two essential DC buses and the nonessential DC bus

Question 12

What buses does the battery provide DC power to?

Answer 12

The two essential buses and the battery bus

Question 13

In the event of a dual TRU failure or double gen failure, how long will the battery power the two essential DC busese?

Answer 13

For approximately 15 minutes at 80% charge

Question 14

What is the minimum voltage required of the battery to connect to the essential DC buses?

Answer 14

18 V

Question 15

How low of a voltage can the battery be at in order to accept a charge?

Answer 15

10 Volts

Question 16

When the battery relay closes (i.e. connects the battery to the essential DC buses), until what voltage will it stay closed?

Answer 16

10 Volts

Question 17

What component deenergizes and disconnects the nonessential bus?

Answer 17

The bus contactor

Question 18

What voltage change causes the bus contactor to drop the non essential DC bus offline?

Answer 18

A voltage change from 28 V to 24 V

Question 19

If the bus contactor is triggered, what is illuminated?

Answer 19

• MASTER CAUTION light
• XMFR RECT OUT light
• CAUTION, CAUTION voice message 1.5 seconds after the Master Caut light

Question 20

Until what voltage does the battery supply DC power to the essential busses?

Answer 20

Until 10 V

Question 21

A single TRU failure generates what warning tones and signals?

Answer 21

A PFL fault and an AVIONICS alert on the HUD/MFD

Question 22

What are the only three times that battery power is required?

Answer 22

1. During starts when the APU is not used
2. When both TRUs fail
3. When both generators are inop or drop off-line