EGSA Generator and Alternator Principles 2

Question 1

What is the primary function of slip rings in an AC alternator?

Accepted Answer

Transfer current to the rotating field winding

Answer

Slip rings provide a continuous electrical connection to the rotating field winding, supplying DC excitation current without interruption.

Question 2

In a synchronous generator, what happens to the output frequency if the rotor speed increases by 10%?

Accepted Answer

Frequency increases by 10%

Answer

Output frequency is directly proportional to rotor speed (f = P×N/120), so a 10% speed increase produces a 10% frequency increase.

Question 3

Which type of rotor is most commonly used in high-speed steam turbine-driven generators?

Accepted Answer

Cylindrical (round) rotor

Answer

Cylindrical rotors are used in high-speed (3600 RPM) turbo-generators because their smooth surface minimizes windage losses and mechanical stress.

Question 4

What is meant by 'armature reaction' in a synchronous generator?

Accepted Answer

Effect of armature current magnetomotive force on the main field flux

Answer

Armature reaction is the distortion and weakening of the main magnetic field caused by the magnetomotive force produced by load current in the armature windings.

Question 5

A 4-pole alternator must rotate at what speed (RPM) to produce 60 Hz output?

Accepted Answer

1800 RPM

Answer

Using f = P×N/120: N = 120×60/4 = 1800 RPM for a 4-pole machine at 60 Hz.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Generator and Alternator Principles 2