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Flashcards in AC Generators Deck (14)
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1

2 main parts to AC generators

Stator which carries 3 pairs of field windings - stationary

Rotor which carries an electromagnetic field

2

Why do we use 3 pairs of windings - AC generator

Allows us to get a 120* spilt

3

Advantages of 3 phase AC

Higher efficiency

Fewer conductors required for transmission and distribution

3 phase motors have better characteristics than single phase

Can use the same power supply for single and 3 phase

4

2 different types of connections for AC

Star/Y connection

Delta or mesh connection

5

Star/ Y connection

Centre goes the the a/c unipole system

Allow us to supply single phase or 3 phase

Delta or mesh connection - only 3 phase

6

Phase voltage

Between star point or neutral point to one of the phases (Vp)

7

Line voltage

Potential difference across any 2 lines/phases in the star connection (VL)

8

When is the star connected system balanced

When it is supplying equal loads in each line then the magnitude of the phase voltage for each line is the same

9

Having the neutral point in the star connection system wired to earth allows

Generator to feed unbalanced loads

Easy to access phase voltages

Majority of the a/c AC generators are wired in star connection

10

Freq formula for an AC generator

Freq = NP/60

N = speed (RPM)

P = number of poles

11

Phase rotation - implications of having a negative phase sequence

Results in the 3 phase motors running in the wrong direction

3 phase power supplies must have a positive phase sequence - ABC

12

Brushless generator

No arcing/sparking

Instead of using battery - uses a small magnet driven from the engine - AC is created and then to DC via a voltage regulator

13

In order to produce 400Hz the generator needs to be spun at

8,000RPM

14

Constant speed drive unit what is it

Hydraulic pump - swash plate constant pressure pump

Drives a hydraulic motor to dive the output to the generator

Self contained system