DC System

Question 1

What does the #1 or #2 DC GEN caution light tell you?

Answer 1

The respective DC generator is off-line

Question 2

What does the L TRU or R TRU caution light tell you?

Answer 2

The respective TRU is off-line

Question 3

With the AUX, main and battery master on, as well as the bus tie closed, which buses are powered?

Answer 3

The main and AUX battery buses
L and R essential buses,
L and R main feeder buses

Note the secondary feeder buses are not powered

Question 4

If the AUX battery indicator on the overhead panel had 0.30, what does this tell the pilot? How would the pilot know if it was discharging?

Answer 4

The battery is either charging or discharging at 30% of the maximum rated capacity.
If there was a flashing - it is discharging.

Question 5

The Battery bus supplies continues 24v power for what?

Answer 5

Fire extinguisher discharge circuits 
Emergency fuel/hydraulic shut-offs 
APU manual fire discharge circuit 
Dome lights 
boarding lights 
Emergency lights control box 
PA system through a relay in the emergency lights system

Question 6

Can batteries be charged by DC external power? Are there any special requirements for this?

Answer 6

Yes but only the main battery with Mod8/2066, however battery charge rate and temperature must be continually monitored.

Question 7

How many temperature sensors does each battery have? What are they connected to?

Answer 7

2, one connected to the battery temperature indicator, the other to the MAIN BAT HOT or AUX BAT HOT warning light.

Question 8

If a battery temperature sensor fails how is the pilot notified?

Answer 8

A yellow light illuminates adjacent to the temperature indicator.

Question 9

If the battery temperature display fails, how is the pilot notified?

Answer 9

A single yellow light segment appears at the 60 degree C mark on the affected battery temperature scale.

Question 10

If the MAIN BATTERY caution light appears, what does this tell the pilot?

Answer 10

The main battery is disconnected from the right main feeder bus

Question 11

Where are the GCUs and BBPU found in the aircraft?

Answer 11

Below the co-pilots circuit beaker panel

Question 12

The DC generator is mounted on which gearbox?

Answer 12

Accessory gearbox

Question 13

How can a pilot shut down a TRU?

Answer 13

By pulling the circuit beaker in accordance with a QRH checklist.

Question 14

If the #1 or #2 DC GEN HOT caution light appears, is the generator automatically taken off-line?

Answer 14

No, the generator needs to be manually taken off-line.

Question 15

If both DC generators fail, will the system still be powered? Is there enough power?

Answer 15

Yes, the DC logic will close the left and right bus tie contractors allowing the secondary feeder buses to power the system.
The secondary feeder buses struggle so power is slowly being drawn from the batteries.

Question 16

What caution lights indicate a ‘ loss of generated power’

Answer 16

Both DC GENs and both AC GENs

Both DC GENs and either one or both TRUs

Question 17

What does the BBPU do? How does it work?

Answer 17

It detects bus faults by monitoring the GCUs for generator over current conditions.

It responds in 2 stages, first taking the DC bus off-line opening the main and both secondary bus ties (DC BUS caution illuminates). If over current still exists after 7 seconds, the BBPU then signals the GCU to shut down the affected generator and isolates the affected battery from the faulted main feeder bus.

Question 18

DC BUS, #1 DC GEN, AUX INV and AUX BATT

DC BUS, #2 DC GEN, and MAIN BATT respectively indicate what faults? What checklist should be called for?

Answer 18

Left and right Main DC bus fault respectively.

Call for MAIN DC BUS FAULT checklist.

Question 19

Following a MAIN DC BUS FAULT, how do you know if the generator or bus caused the problem?

Answer 19

As per QRH reset the main bus fault reset. if DC BUS caution light goes out and stays out the generator was the issue. If the DC BUS caution light stays on, the DC bus was the problem so you’ll lose the services from the respective bus.

Question 20

When external DC power is applied, what protects the DC System? When will the protection Activate? How is it powered

Answer 20

An over voltage protection relay automatically disconnects external power from the system when external power at the receptical exceeds 31.5 volts.
The relay is powered by the essential bus which is why the battery master must be on prior to connecting ground power.

Question 21

Which bus does the APU feed power to?

Answer 21

Right main feeder bus. This bus can then power the left main feeder bus, both essential buses and both secondary feeder buses

Question 22

During ground operations, what is the maximum DC generator loadmeter reading?
Is the value ever allowed to be exceeded

Answer 22

0.7. Yes, for internal battery starting, the load may be exceeded for up to 1 minute.

Question 23

What happens when you switch the battery master on?

Answer 23

The essential buses are powered. The main bus powers the right essential bus and the AUX battery powers the left. However either battery can power both essential buses.
It also enables the main battery to power the right main feeder bus when the main battery is is selected on.

Question 24

What are some things powered by the essential buses?

Answer 24

Advisory and caution lights 
EHSI 1 and EADI 1 and SYM gen1
AHRS 1 
Eng ECUs 
Eng Instruments (Torque, ITT, Np, Nh, oil T and P) 
VHF Com 1 and nav 1 
HYD quan and ind 
Hot BATT bus stuff 
Rad alt

Question 25

What are some things powered by the right main bus? (particular important if considering leaving main battery on for Ditching)

Answer 25

Rad alt 2 
FGC 2 servo and FGC 2
Alt alert 
ADC 2 
EADI & EHSI 
SYM GEN 2 
VOR 2 ADF 2 & DME 2

Question 26

What are some things powered by the left main bus? (important if considering leaving main and AUX BAT on for Ditching with bus tie closed)

Answer 26

HF Com 
Rad alt 1
FGC 1 
audio alt alert 
ADC 1