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Flashcards in AC Generators Deck (14)
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2 main parts to AC generators

Stator which carries 3 pairs of field windings - stationary

Rotor which carries an electromagnetic field


Why do we use 3 pairs of windings - AC generator

Allows us to get a 120* spilt


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


2 different types of connections for AC

Star/Y connection

Delta or mesh connection


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


Phase voltage

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


Line voltage

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


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


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


Freq formula for an AC generator

Freq = NP/60

N = speed (RPM)

P = number of poles


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


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


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



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