AC Motors

Question 1

List 4 advantages of an AC motor.

Answer 1

Require less maintenance
More efficient
Cheaper
More compact

Question 2

What is the main disadvantage of the AC motor?

Answer 2

Very difficult to vary the speed.

Question 3

List the 2 main components of the AC motor.

Answer 3

The stator
The rotor

Question 4

What causes movement in a 3-phase induction motor?

Answer 4

The windings of the stator produce a rotating magnetic field.

Question 5

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

Answer 5

Squirrel cage induction motor

Question 6

List the components of a squirrel cage rotor.

Answer 6

Non-drive end bearing
Copper end ring
Copper bars
Drive and bearing
Copper end ring

Question 7

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

Answer 7

Rotating field induces a current in the copper bars of the rotor. Current causes a magnetic field to be det uo around the rotor. Magnetic field set up in the rotor is opposite in polarity to theagmetic field in the stator. Inter action between this field, the rotating field of the stator causes the rotor to ‘follow’ the rotating g field therefore giving you rotation.

Question 8

Why is there there less maintenance on an AC motor?

Answer 8

There is no electrical connection to the rotor and therefore no need for brushed and slip rings.

Question 9

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

Answer 9

It will keep rotating due to being connected in 2 ways star and delta.

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

The motor will continue to operate at a reduced speed and experience vibrations.