AC Motor

Question 1

List 4 advantages of an AC motor

Answer 1

AC motors require less maintenance, ac motors are more efficient than DC motor

Question 2

What is the main disadvantage of an AC motor?

Answer 2

Difficult to vary speed.

Question 3

List the 2 main components of the AC motor?

Answer 3

Rotor and stator

Question 4

What causes movement in a 3-phase induction motor?

Answer 4

The rotating magnetic field generated by the stator.

Question 5

What is the most common type of AC motor used on HM Ships?

Answer 5

Squirrel cage

Question 6

List the components of a squirrel cage rotor?

Answer 6

Non-driving end bearing, copper end ring, copper bar, copper end ring, drive end bearing, shaft.

Question 7

How does the rotating magnetic field from the stator cause rotor to rotate?

Answer 7

The rotating field induces a current in the copper bar of the rotor.
This current causes a magnetic field to be set up around the rotor.
The magnetic field set up opposite in polarity to the magnetic field in the stator.
The inter-action between the two magnetic field causes the rotor to ‘follow’ the rotating field.

Question 8

Why is there less maintenance on an AC motor?

Answer 8

There is no electrical connection to the rotor, therefore no requirement for brushes and slip ring.

Question 9

What do you think would happen to a running 3-phase AC motor, if it were to lose 1-phase of its input?

Answer 9

It would start to heat up, lose power, start to vibrate heavily, generate excessive noise

Question 10

If a shutdown 3-phase AC motor were to lose 1-phase of its input, what affect do you think this would have on starting?

Answer 10

It will not start.