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

Rectify AC to DC output

Answer

Regulate voltage output

Answer

Reduce armature reaction

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

Frequency decreases by 10%

Answer

Frequency remains the same due to AVR

Answer

Frequency doubles

Question 3

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

Accepted Answer

Cylindrical (round) rotor

Answer

Salient pole rotor

Answer

Claw pole rotor

Answer

Wound rotor

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

Voltage drop across the armature resistance

Answer

Mechanical reaction torque on the stator

Answer

Thermal expansion of armature windings

Question 5

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

Accepted Answer

1800 RPM

Answer

3600 RPM

Answer

1200 RPM

Answer

900 RPM

Question 6

What is the purpose of damper windings (amortisseur windings) in a synchronous generator?

Accepted Answer

Dampen rotor oscillations and suppress hunting

Answer

Increase field excitation during load surges

Answer

Provide backup excitation if the AVR fails

Answer

Reduce harmonic distortion in output voltage

Question 7

How does increasing field excitation beyond the unity power factor point affect a synchronous generator connected to an infinite bus?

Accepted Answer

It causes the generator to supply reactive power (over-excitation)

Answer

It increases real power output

Answer

It causes the generator to absorb reactive power (under-excitation)

Answer

It reduces the terminal voltage