Electrical System

Question 1

What is the purpose of the electrical system?

Answer 1

To provide AC and DC electrical power for the aircraft

Question 2

What are all of the sources of AC power?

Answer 2

1. Main generators
2. APU generator
3. External power

Question 3

What is the primary source of AC power?

Answer 3

The two main generators

Question 4

What is the secondary source of AC power?

Answer 4

The APU generator

Question 5

What are the components of the AC power system?

Answer 5

• Main generators
• APU generators
• Generator Control Unit (GCUs)
• External power connection
• AC electrical buses

Question 6

Describe the main generators.

Answer 6

Provides 115 volts AC power
* Oil cooled (lubricated by XMSN oil)
* 3-phased
* 400 Hz

Question 7

How are the main generators driven?

Answer 7

Via the accessory module for its respective engine

Question 8

What does the GCU do?

Answer 8

• Connects each respective generator to the AC electrical bus system
• Regulates generator output
• Protects system components and monitors voltage level and frequency

Question 9

What are the five AC electrical buses?

Answer 9

• No. 1 AC Primary Bus
• No. 2 AC Primary Bus
• AC Essential Bus
• AC Secondary Bus
• AC Monitor Bus

Question 10

What happens to the APU generator with both main generators operating?

Answer 10

The APU generator will not be connected to any of the AC buses

Question 11

What is the AC Bus distribution with both main generators operating?

Answer 11

No. 1 Generator (left):
* No. 1 AC Primary Bus
* AC Essential Bus
* AC Secondary Bus

No. 2 Generator (right):
* No. 2 AC Primary Bus
* AC Monitor Bus

Question 12

What is the AC Bus distribution with only one main generator operating and APU off?

Answer 12

Operating Generator:
* No. 1 AC Primary Bus
* No. 2 AC Primary Bus
* AC Essential Bus

The AC Monitor bus and AC Secondary bus will not be powered.

Question 13

What is the AC Bus distribution with one main generator operating and the APU on?

Answer 13

Operating Generator:
* No. 1 AC Primary Bus
* No. 2 AC Primary Bus
* AC Essential Bus

APU Generator:
* AC Monitor Bus
* AC Secondary Bus

Question 14

What is the AC Bus distribution with the APU generator operating as the only source of AC power?

Answer 14

APU Generator:
* No. 1 AC Primary Bus
* No. 2 AC Primary Bus
* AC Essential Bus

The AC Monitor bus and AC Secondary bus will not be powered.

If the back-up pump is ON, then the copilot/center windshield anti-ice will be disabled.

Question 15

What does placing the generator switch in the ON position mean?

Answer 15

Connects the respective generator output to the AC distribution system

Question 16

What does placing the generator switch in the OFF/RESET position mean?

Answer 16

• OFF: Disconnects the generator from the AC distribution system
• RESET: Resets the GCU if it was either disabled or disconnects from the AC distribution system

Question 17

What does placing the generator switch in the TEST position mean?

Answer 17

Tests the generator AC output without connecting it to the AC distribution system

Question 18

What is the primary source of DC power?

Answer 18

The two converters

Question 19

Describe the DC converters.

Answer 19

Converts 115 volts AC power into 28 volts DC power and supplies that power to the DC distribution system

Question 20

What powers the DC converters?

Answer 20

They are powered by the NO. 1 and NO. 2 AC Primary buses

Question 21

What is the secondary source of DC power?

Answer 21

A 24 volt DC Nickel-Cadmium battery

Located in the co-pilot (left) seat well

Question 22

With an 80% charge, what is the normal battery life for day operations?

Answer 22

11 minutes

Question 23

With an 80% charge, what is the normal battery life for night operations?

Answer 23

9 minutes

Question 24

What is purpose of the battery?

Answer 24

• To start the APU
• Power the Battery Utility Bus
• Provide an emergency source of DC power

Question 25

What is the purpose of the battery analyzer/conditioner?

Answer 25

Monitors the battery system for: * Fault conditions * Battery charge * Internal temperature * Cell conditions Provides battery-charging capability

Question 26

When does the battery analyzer/conditioner charge the battery?

Answer 26

Whenever AC power is available and the BATTERY switch is in the ON position

Question 27

What are the five DC buses?

Answer 27

1. No. 1 DC primary bus 2. No 2 DC primary bus 3. DC essential bus 4. Battery bus 5. Battery utility bus

Question 28

What is the DC Bus distribution with **both converters operating**?

Answer 28

NO. 1 Converter (left): * No. 1 DC Primary bus * DC Essential bus * Battery bus NO. 2 Converter (right): * No. 2 DC Primary bus Battery: * Utility bus

Question 29

What is the DC Bus distribution with **only the battery operating (more than 35% charge)**?

Answer 29

Battery: * DC essential bus * Battery bus * Utility bus **The No. 1 and No. 2 DC Primary buses will not be powered.**

Question 30

What is the DC Bus distribution with **only the battery operating (less than 35% charge)**?

Answer 30

Battery: * Battery bus * Utility bus **The No. 1 and No. 2 DC Primary buses and DC Essential bus will not be powered.**

Question 31

What would be lost if both DC converters are lost?

Answer 31

Both FDs and MDs would be lost

Question 32

When does the GCU underfequency protection feature kick in?

Answer 32

* In flight, the main generators are dropped @ ~80% Nr * With Weight on Wheels, the main generators are dropped when below 94% Nr (a minimum of 97% Nr is necessary for the generators to be reconnected)

Question 33

When does the BATTERY LOW CHARGE caution appears?

Answer 33

When the battery is at or below 40% a fully charged state

Question 34

What occurs when the battery is at 35% charge?

Answer 34

The DC Essential Bus will be lost

Question 35

What occurs when the Battery is at 30% charge?

Answer 35

Battery power may not be sufficient to activate the fire extinguisher CAD (Cartridge-Actuated Device)

Question 36

**Check** Circuit Breaker

Answer 36

Visually observe the circuit breaker position. Do not change condition.

Question 37

**Pull** Circuit Breaker

Answer 37

If the circuit breaker is in, pull the circuit breaker out. If the circuit breaker is out, do not change condition.

Question 38

**Reset** Circuit Breaker

Answer 38

If the circuit breaker is out, push the circuit breaker in. If the circuit breaker is in, do not change condition. **Popped circuit breakers may be reset only once.**

Question 39

**Cycle** Circuit Breaker

Answer 39

If the circuit breaker is in, pull the circuit breaker out, and then push the circuit breaker back in. If the circuit breaker is out, do not change condition.

Question 40

How is automatic bus switching accomplished?

Answer 40

Via the bus tie (can be the AC or DC)

Question 41

What is a bus tie?

Answer 41

A switchable electrical connection between two or more separate bus systems

Question 42

How can you tell the difference between a dual generator and dual converter failure?

Answer 42

The STAB indicator provides a readout with AC power; the OFF flag would be displayed if there is no AC power. * **Secondary Indication:** If the bezel keys around the MD/FD are still illuminated, then it is a dual-converter failure.

Question 43

What does the APU GEN ON advisory indicate?

Answer 43

That the APU generator is the sole source of power

Question 44

With WOW (Weight on Wheels) switch activated, what occurs when Nr droops below 94%?

Answer 44

The GCU removes the main generator from the AC power distribution system

Question 45

In flight, when would the generators fall offline?

Answer 45

The generators would remain online until Nr decreases to ~80% Nr

Question 46

What minimum Nr is required for the GCU to reconnect the generators to the AC electrical distribution system?

Answer 46

A minimum of 97% Nr