AC Motors

Question 1

List 4 advantages of an AC motor.

Answer 1

1. More efficient
2. More compact
3. Less maintenance
4. Cheaper (to build and maintain)

Question 2

What is the main disadvantage of an AC motor?

Answer 2

Difficult to vary its speed (extra, external equipment is required)

Question 3

List the 2 main components of the AC motor

Answer 3

1. Stator
2. Rotor

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

The squirrel cage induction motor

Question 6

List the components of a squirrel cage rotor

Answer 6

• Drive end bearing
• Non drive end bearing
• Copper bars
• Copper end ring

Question 7

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

Answer 7

The interaction between the two magnetic fields 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 rings

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

• Keep running
• Lose power
• Vibrate heavily
• Heat up
• 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