ELECTRICAL POWER SYSTEMS

Question 1

1. Describe the electrical system:

Answer 1

• Single-loop
• 28-volt DC
• Triple-fed system w/ a negative ground.

Question 2

2. What supplies normal DC power?

Answer 2

during normal operation:

• 24-volt nickel-cadmium battery, or a 24-volt lead-acid battery
• two 28-volt
• 300-ampere starter-generators

Question 3

3. Where is the battery located?

Answer 3

RH wing center section between the RH nacelle and fuselage

Question 4

4. Battery power is connected to which buses?

Answer 4

• the battery bus,
• the center bus,
• the triple-fed bus.

Question 5

5. What protects the five electrical buses?

Answer 5

The five primary buses are individually protected by:

1. current sensors
2. limiters
3. diodes
4. relays.

Load-shedding is accomplished by isolating a faulty bus from those that are still functional, thereby preventing a failure of the entire electrical system.

Question 6

6. Which relays close when the Battery Switch is placed to ON?

Answer 6

• Battery relay
• Battery Bus Tie relay.

Question 7

7. Describe Automatic Load Shedding?

Answer 7

Automatically sheds the generator busses as necessary to reduce excess loads.

Question 8

8. What is on the Dual Fed Bus?

Answer 8

• L Engine Fire Ext
• R Engine Fire Ext
• Cabin Entry Lights

Question 9

9. Explain the functions of the Generator Control Unit?

Answer 9

• Voltage regulation
• Overvoltage/over-excitation protection
• Reverse current protection;
• Paralleling/load sharing (within 10%)
• Isolates failed/Off gen from its bus.
• Cross-gen start current limiting;

Question 10

AC ELECTRICAL SYSTEM

10. Describe the AC electrical system.

Answer 10

1. 115-VAC and 26-VAC,
2. single phase,
3. It operates on 28 VDC and provides AC power to certain avionics and electrical equipment.
4. 400 Hz system.
5. The system consists of two static inverters, two bus-transfer relays, an AC power monitor circuit card and associated switches, circuit breakers, and annunciators.

Question 11

AC ELECTRICAL SYSTEM

11. What will cause the red AC Bus annunciator light to illuminate?

Answer 11

1. fault on the AC bus
2. loss of AC power

Question 12

12. Where are the AC Bus circuit breakers located?

Answer 12

On the fuel panel CB panel.