NATOPS CH2.6 Electrical System

Question 1

What is the primary source of electrical power and where does it come from?

Whats the secondary source?

Answer 1

AC is the primary source of power and can be supplied by the 2 main generators, the APU generator, or from external power (technically the Engine Alternator also supplies AC power)

DC is the secondary source of power and is supplied by the the 2 DC converters and a 24V DC NICAD Battery

Question 2

Describe the main Generators and the APU Generator

Answer 2

The main generators are oil cooled 30/45-kVA, 115 Volt AC, 3 Phase, 400hz Generators

The APU generator is a 35-kVA, 115 Volt AC, 3 Phase, 400hz Generators

Question 3

What does the Generator Control Unit do and what does it protect against?

What about for external power?

Answer 3

The GCU connects each respective generator to the AC electrical bus, it regulates generator output and protects against

• Overvoltage
• Undervoltage
• Feeder Fault
• Under Frequency

The external power does all of the same but includes protections for

• Phase Rotation
• Over Frequency

Question 4

When do the Generators drop out?

When will the reconnect?

Answer 4

If N_r Drops below 94% while on the ground, the GCU will remove the main generators from the distribution system

In flight underfrequency protection is removed allowing generators to remain online until 80% a minimum of 97% will be required to reconnect the generators

Question 5

How does the External Power know to connect to the Aircraft?

Answer 5

External power includes a 4-amp circuit breaker that places a 2-amp draw on the power cable when connected to the aircraft.

Question 6

Name the AC electrical power buses

Answer 6

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

Question 7

Which Bus is powered by which Generator, what if a generator falls offline?

Answer 7

With both generators operating normally, the No.1 Gen powers the No.1 AC Primary, the AC Essential, and the AC Secondary Buses

The No.2 Gen powers the No.2 AC Primary and the AC Monitor Bus

If one generator falls off, bus switching will switch the loads to the available generator, if the APU is on that generator can also be used to help

Question 8

What are the three pigs and which buses are they connected to?

Answer 8

• Backup Hydraulic Pump
  
  • Connected to the No.1 AC Primary Bus (always powered if required)
• Mission Avionics
  
  • Connected to the AC Secondary Bus, along with the Tail rotor De-Ice
• Main Rotor De-Ice System
  
  • Connected to the AC Monitor Bus (has the lowest priority)

Question 9

When will the bus system begin to shed excess loads?

Answer 9

• If only the APU Gen is on, you will lose the Secondary and Monitor Buses
• With one generator and the APU, you will lose the monitor bus if you have both the backup pump on and mission power.
• With one Main Gen and backup off, you lose only the Monitor
  
  • With backup on, you will also lose the secondary

Question 10

How do you connect external power and when will it be disconnected?

Answer 10

To connect external power, the EXT PWR switch must be toggled RESET , then ON

It will automatically be disconnected when either the APU or main Gens are brought online

Question 11

When will the GEN Caution appear?

Answer 11

1. Respective generator isn’t supplying power to the buses
2. The generator is selected off
3. Failure of the generator, GCU, contractory control relay, or a wiring fault

Question 12

When will you get the APU GEN Caution?

Answer 12

1. Failure of the APU driven generator, GCU, contactor control relay, or wiring fault
2. APU Generator is selected on, APU started but has not reached operating limits

Question 13

What is the purpose of the Battery?

How long is its life?

Answer 13

The Battery is the primary source of power for starting the APU, and a secondary source of power for the DC Essential and the Battery bus

With 80% charge, normal battery life is 11 min for day ops, and 9 min for night ops

Question 14

What is the purpose of the battery Analyzer/Conditioner?

Answer 14

Located in the copilot seat well, it monitors the battery system for:

• Fault conditions
• Battery charge
• Internal temperature
• Cell conditions
• Provides battery charging capabilty

Question 15

Where does the Battery Analyzer/Conditioner recieve it’s power from?

Answer 15

It recieves AC power from the No.2 AC Primary bus (to work) and DC power from the No.2 DC Primary Bus (DC Charging)

Question 16

What are the DC Buses?

Answer 16

• No. 1 DC Primary Bus
• No. 2 DC Primary Bus
• DC Essential Bus
• Battery Bus
• Batery Utility Bus

Question 17

What happens if one or both of the DC buses fail?

Answer 17

If one DC bus fails the remaing bus will pick up the loads of the failed bus

If both buses fail the No.1 and No.2 Primary DC buses are dropped, power is supplied to the Battery bus, and Battery Utility bus. The Battery will continue to power the DC Essential bus until it drops below 35% charge after which it will also be dropped.

Question 18

What happens if the power drains on the battery?

Answer 18

At 40% the BATTERY LOW CHARGE caution will appear

At 35% charge the DC essential bus is dropped

Below 30% charge, battery power may not be sufficient to active the fire extinguisher Cartridge-Actuated Device (CAD)