VII With your partner match these questions with the answers bellow.

1 What is the most common method of voltage regulation for ac generators?

2 Why would we use a permanent magnet on the generator rotor in place of

exciter windings?

3 What happens when magnetic fields of alternating polarity pass across the

armature windings?

4 What controls the voltage induced into the armature windings?

5 What must ac generator control systems protect against?

6 What is the purpose of the rotating three-phase rectifier in a brushless generator?

7 What is the chief advantage of having dc exciter units integrated into ac

generators?

8 What is the only moving mechanical part in a solid state voltage regulator?

Answers:

a The most common method of voltage control in power generating systems is

varying the current to the generator exciter winding (sometimes called field

winding).

b This method uses a permanent magnet on the generator rotor in place of exciter

windings, which simplifies generator construction. This type of regulation must

be used with systems that supply constant loads and have a limited capacity.

c When magnetic fields of alternating polarity pass across the armature

windings, ac voltage induction occurs.

d Control of the voltage induced into the ac generator windings depends on three

things:

1. The number of turns of conductor per winding 2.The speed of the magnetic field

passing across the winding (generator revolutions per minute [rpm]) 3.The

magnetic field strength. The number of turns per winding and the number of

windings are set during generator manufacture.

e Ac generator control systems must contain circuits to protect against under

voltage and overvoltage, underfrequency and overfrequency, and improper

phase sequence.

f The auxiliary dc generator (called the exciter) or a rotating three-phase

rectified ac exciter generator supplies this current. The exciter is on the

same shaft as the ac generator to make it an integral part of the generator.

g The chief advantage of exciter units is that each generator has its own

independent source of excitation. No external source of electric power is

necessary for generator operation.

h One type of voltage regulator that has no mechanical moving parts (except the

exciter control relay) is the solid-state regulator. The ac generator output flows to

the voltage regulator, which compares it to a reference voltage.