AC Generation

Question 1

AC Generation in Modern AC

Answer 1

115V 3 phase at 400Hz for distribution system

26V at 400Hz for some flight instruments

115/200V

Question 2

Where Is AC commonly from in AC?

Answer 2

Engine
APU
Hydraulically
RAT (Emergency Only)

Question 3

DC TO AC in AC Generation

Answer 3

Inverter

Question 4

Advantages to AC

Answer 4

No loss of power and transfer over longer distance - AC Changed from one voltage to another via transformer

Simple and light weight construction than DC

Changed into DC using TRU

Question 5

Constant Frequency AC Generation

Answer 5

Provide constant freq

Engine drive hydraulic pump which drives a hydraulic motor

Output of pump and motor depends on swash plate angle

Question 6

What controls swash plate in constant freq CSDU

Answer 6

Controlled by a device called a speed governor

Speed governor controlled by load controller

Question 7

AC Generator Frequency Wild

Answer 7

Direct driven by engine gearbox rpm variation

Used only for purely resistive components

Cannot connect 2 frequency gens in parallel

Question 8

CSDU or IDG Disconnect protocol

Answer 8

Disconnect can only be operated when engines are running

Only reset by engineer on ground

Guarded switch

Question 9

CSDU failure

Answer 9

Quill drive - weak link which break if damaged

Low oil P
Low oil level
High oil Temp

Question 10

IDG

Answer 10

Integrated drive generator

CSDU and generator combined
- Generator stator can be cooled by oil rather than air

Smaller unit for same amount of power output

Question 11

3 Phase AC Generator (Alternator)

Answer 11

More efficient way of generating electricity using 3 phase AC generator

Magnetic field on rotor
Conductors (armature) on stator

3 phase rectifier:
- Consists of 6 diodes
- Only 4 diodes use at one time

Capacitor used for output smoothing

Question 12

Advantage of multi phase AC

Answer 12

Entire stator used
Motors run more smoothly
High power spreads the load across all 3, but current at each phase is lower than single

Question 13

Generator Control Breaker or Generator Load Contractor role

Answer 13

Connects generator to generator busbar

Question 14

CSDU/IDG Oil Leaks

Answer 14

Small engine oil leak could be a large CSDU or IDG oil leak

Question 15

Permanent Magnet Generators

3 Phase ac Gen - Brushless

Answer 15

Provide emergency power
Made of hard iron rather than electromagnet

EG RAT system

Brushless AC Generator - no physical connection between rotor and static side

+ No need for slip rings and brushes
+ Reliable
+ High power to weight ratio

• PMG - Only used to start the main field when generator starts up
• Main exciter Normal Ops put voltage through coils
• Main generator

Also provides excitation voltage for generators and control output voltage -

Question 16

What is a CSD

Answer 16

Constant Speed drive
Provide constant speed to rotor irrespective to engine speed
Within 5% of 400hz
Engine must be running to disconnect CSDU

Question 17

CSDU Disconnecting principles

Answer 17

Not to be used on ground or when engines not running
CSD cannot be reset in flight needs to be reset by engineers
Physically separates CSD from engine preventing damage

Question 18

Y star connection

Answer 18

Allows for unbalanced loads and can lose a phase without impacting other two
Output 115v at each line

Question 19

A differential fault is…

Answer 19

Difference between generator output current and the bus bar input current

Suggesting earth fault between the two

Question 20

Generators in parallel must…

Answer 20

Be the same voltage sync frequency and phases aligned
Then can connect to tie bus bar

Question 21

Generator failure and bus bar

Answer 21

Generator control breaker will disconnect the generator from it bus

Question 22

Frequency of current provided by alternator depends on

Answer 22

Rotation speed

Freq = (RPM x number of pairs) / 60

Question 23

Frequency is defined as

Answer 23

The number of oscillations per second in hertz

Question 24

Equation for gen output frequency

Answer 24

Rotor RPM x number of pole pairs
————————————————
60

Question 25

How do you calculate pairs of poles

Answer 25

Frequency / RPM x 60

Question 26

Generator Control Unit does what

Answer 26

Fault sensed by GSU and open circuit breaker - used in parallel bus systems for protection - connected to each to monitor all in phase

Question 27

Frequency of an AC generator is dependent on

Answer 27

RPM of the rotor
Number of pair poles or phases

Hz = rpm x poles/60

Question 28

Generator control unit protects against what

Answer 28

AC gen over/under voltage
Under frequency
Over speed
Excess current
Differential fault

Question 29

Frequency Formula

Answer 29

RPM X Number of pole Paris

60

Question 30

Reactance

Answer 30

Measured in ohms - form of resistance reaction to current flow - back EMF

Question 31

Apparent Power

Answer 31

Measured in volt-amps

Question 32

AC generators are rated in

Answer 32

KVA

Question 33

Reactive power vs real power

Answer 33

Reactive power is wasted
Real power is what is being used

Question 34

Frequency of an AC generator is dependent upon

Answer 34

RPM of the rotor
Number of phase windings in the stator

Question 35

To increase the real load taken by paralleled ac generator

Answer 35

Generator drive torque is increased

Question 36

PMG in rotating field AC generator

Answer 36

Referred to as the pilot exciter provides the voltage regulator with power to feed main exciter.

Feeds voltage to field rotor and generator can start producing power

PMG is no longer required after start up

Question 37

Where would you find a frequency wild generator on what type of engine?

Answer 37

Turbo prop

Question 38

IDG vs CSD

Answer 38

Integrated drive generator is a electrical generator which provides electricity for the aircraft. IDG provides electrical power for all the aircraft systems and consists of a CSD

CSD is part of an IDG