AC Motors Flashcards
What are 4 advantages of an AC motor?
More compact
Less maintenance
Cheaper to build and maintain
More efficient than DC motors of the same size
What is the main disadvantage of an AC motor?
Difficult to vary its speed (extra, external equipment is required)
List the two main components of the AC motor.
Rotor
Stator
What causes movement in a 3-phase induction motor?
The rotating magnetic field generated by the stator
What is the most common type of AC motor used on HM Ships?
The squirrel cage induction motor
List the components of a squirrel cage rotor
Non-drive end bearing
Copper end ring x2
Drive end bearing
Copper bars
How does the rotating magnetic field from the stator cause rotor to rotate?
The rotating field induces a current in the copper bars of the rotor, This current causes a magnetic field to be set up around the rotor, The interaction between the two magnetic fields causes the rotor to “follow” the rotating field
Why is there less maintenance on an AC motor?
There is no electrical connection to the rotor, therefore no requirement for brushes and slip rings
What do you think would happen to a running 3-phase AC motor, if it were to lose 1-phase of its input?
It would keep running, It would lose power, It would start to vibrate heavily, It would start to heat up, It would start to generate excessive noise
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?
It will not start
What supply is used for most AC motors on board?
440 V, 60 Hz, 3 phase
When are AC motors not used on board?
Where close speed control is required.
What are the two ways of connecting motor windings?
Star and delta
What is the rotor made from in an AC rotor.
Thin strips of steel.
