AC Generators

Question 0

How does a current transformer sense the amount of current in a wire?

Answer 0

Through electromagnetic induction

Question 1

What are the required loads for a generator to supply to an aircraft?

Answer 1

Loads to a normally working system; essential loads after failed of and prime movers; essential loads after failure of any engine or multi-engine aircraft; essential loads for which AC source of power is required after any failure in one power supply system

Question 2

How does an auto transformer work?

Answer 2

A tap contacts a single transformer coil at a point to output the exact required voltage.

Question 3

What is the purpose of a bus bar?

Answer 3

A bus bar is used to distribute power over a set of contact points.

Question 4

What are three circuit protection devices?

Answer 4

Circuit breakers, fuses, and current limiter

Question 5

What are the three types of circuit breakers?

Answer 5

Thermal, magnetic, thermal-magnetic

Question 6

What are the three types of fuses?

Answer 6

Normal, time delay, and very fast acting

Question 7

What are the 2 types of switches?

Answer 7

Toggle and rotary

Question 8

What are the requirements for aircraft wiring?

Answer 8

Design temperatures, flexibility, resistance, applied voltage, abrasion resistance, strength, insulation, weight, and current flow.

Question 9

How many strands are in a small and large wire?

Answer 9

7 or 19 for small.

19 or more for large.

Question 10

What is the difference between relays and solenoids?

Answer 10

Solenoids have a moveable core. Solenoids have heavy contacts that are capable of handling high amounts of current.

Question 11

What are the classifications of relays?

Answer 11

Control relays, power relays (line contractors), revers current relays

Question 12

What are Line contractors used for?

Answer 12

Controlling high voltages.

Question 13

What are special about AC line contractors?

Answer 13

They have three leads, one for each phase.

Question 14

How do reverse current relays work?

Answer 14

The generator powers a relay that, if not powered by the required voltage, opens, and prevents a current from flowing backwards to the generator.

Question 15

What is a negative ground system?

Answer 15

The aircraft skin is a negative ground, providing a ground throughout the aircraft. This helps reduce the wires normally required for return grounds.

Question 16

What is shed and non-shed?

Answer 16

Non-Shed: essential for safe aircraft operation

Shed: convenience, non-essential

Question 17

What are some non-shed systems?

Answer 17

Essential lighting, flight control system, communication and nav radios, other high priority electrical systems.

Question 18

What type of Voltage is used in an aircraft?

Answer 18

115VAC, phase 3, 400 Hz

Question 19

How does a split bus system work?

Answer 19

Each bus can be powered by either generator, isolating the other in the event of failure, and automatically removes shed components

Question 20

What are the types of external sources for AC?

Answer 20

Essex mobile and Hobart power cart, hangar deck and flight line hard-wired AC power

Question 21

How many degrees is the sine wave of either phase from the other?

Answer 21

120*

Question 22

What will a voltmeter read between 2 phases?

Answer 22

200 VAC

Question 23

What will a voltmeter read between a phase and neutral?

Answer 23

115VAC

Question 24

What is the name of the connection of the three phase leads?

Answer 24

Wye Connection

Question 25

What are the components of a simple AC generator?

Answer 25

Pole pieces, armature loop, slip rings, and generator brush

Question 26

What material are generator brushes made of?

Answer 26

High-grade carbon and graphite for the brush.

Copper for the pigtail

Question 27

What is the name of the stationary and rotating components of a generator?

Answer 27

Stationary: Stator
Rotating: Rotor

Question 28

What are the benefits of a brushless generator?

Answer 28

Low maintenance cost, high stability and consistency, better performance t high altitude, require much less iron and weigh less.

Question 29

Describe the PMG process.

Answer 29

The rotor shaft spins a permanent magnet generating a single phase AC current to go to the GCU. The GCU rectifies the voltage to DC and powers an exciter field for a 3 phase generator. The three phase gen goes through a rectifier creating a stable DC exciter. That spins with the shaft creating a rotating field generating 3 phase AC

Question 30

What are the three factors that directly affect generator output?

Answer 30

The speed the armature rotates, number of conductors, the strength of magnetic field (what is controlled by the GCU)

Question 31

What are the functions of GCU protection?

Answer 31

Voltage regulation, reverse current protection, under/over frequency, phase differences, feeder fault (shorts)

Question 32

When is APU power generation used?

Answer 32

Before engine start, during ground maintenance, and in-flight emergency when primary AC fails

Question 33

What are the outputs of a rotary inverter with an input of 28 VDC?

Answer 33

115 VAC, single phase, 400 Hz
115 VAC, three phase, 400 Hz
200 VAC, three phase, 400 Hz

Question 34

What are the types of inverters?

Answer 34

Rotary (PMG and inductor) and Static

Question 35

What is a major safety concern for operating external power?

Answer 35

Never disconnect the external power connector with the aircraft systems running or the external source on.

Question 36

The External Power Monitor will disconnect external power from the aircraft if it senses any of the following:

Answer 36

Under Voltage, over Voltage, under-frequency, over-frequency, improper phase sequence