Electrical

Question 1

What are the 5 AC buses?

Answer 1

AC Bus 1 and 2
AC ESS Bus
AC Standby Bus
AC Gnd Serv Bus

Question 2

What are the 8 DC buses?

Answer 2

DC Bus 1 and 2
DC ESS Bus 1, 2 and 3
Hot BATT Bus 1 and 2
DC Gnd Serv Bus

Question 3

What is the primary source of AC power and how does it work?

Answer 3

AC power provided by engine-driven IDG (Integrated Drive Generators)

Each IDG (located in accessory gear box) consists of a CSD (constant speed drive) giving constant output speed to a 115VAC, 400Hz, 3-phase, 40kVA generator.

Question 4

In normal operation, how is the AC ESS bus powered?

Answer 4

By AC Bus 2

Question 5

What are the 2 secondary sources of AC power?

Answer 5

AC GPU
AC from APU GEN

Question 6

What power does the RAT provide?

Answer 6

Ram Air Turbine
115VAC, 400Hz, 3-phase, 15kVA power

No altitude restriction for RAT deployment

Constant generator speed is obtained through an automatic variable pitch mechanism

Question 7

Airspeed limitation for RAT?

Answer 7

No strict limitation, but below 130kts, DC power is provided by batteries.

Above 130kts, DC power is provided to DC ESS buses by TRU ESS, powered by AC ESS bus

Question 8

What is AC power source priority?

Answer 8

1. Associated IDG
2. APU
3. GPU
4. Opposite IDG

Question 9

What is NBPT system?

Answer 9

No-Break Power Transfer system.

Momentary parallel AC power between two sources, to avoid electrical cuts or transients.

On ground only, duration is in milliseconds.

Question 10

What is recommended to avoid power interruptions?

Answer 10

Wait 30 sec. after N2 is stabilized on one engine before shutting APU off or disconnect GPU

Question 11

What are the primary sources of DC power?

Answer 11

TRUs : Transformer Rectifier Units

Converting 115VAC to 28VDC at 300A.

Question 12

What is the secondary source of DC power?

Answer 12

Two 24VDC, 27Ah batteries.

BATT 1 is located in FWD electronics bay
BATT 2 is located in AFT electronics bay

Question 13

How much time of DC essential loads do batteries provide?

Answer 13

Approx. 10 min.

Question 14

Why is BATT 1 On/Off and BATT 2 is Auto/Off?

Answer 14

Because BATT 2 knob also automatically controls the tie contactor that powers the APU Start bus

Question 15

In case BATT 2 is unavailable, what is the other source of DC power for APU Start bus?

Answer 15

DC GPU.

Not depicted on Electrical Panel, only in the Electrical synoptic page (MFD).

Only available for this bus and for APU start. Won’t provide DC power to the rest of the system.

Question 16

What is the minimal T° for a battery APU start?

Answer 16

-20°C