AC Motors

Question 1

An AC motor which rotates at the same speed as supply frequency is called.

Answer 1

a synchronous motor

Question 2

A three phase AC motor is running at speed on constant load. If one phase goes open circuit, the motor will run at.

Answer 2

same speed

Question 3

Shaded poles in an alternating current motor are intended to.

Answer 3

facilitate starting

Question 4

In a 3 phase motor, if 1 phase is lost, the motor.

Answer 4

remains at the same speed

Question 5

A three-phase motor has the windings.

Answer 5

120° apart

Question 6

To change the direction of a 3-phase induction motor you would.

Answer 6

swap two of the stator connections

Question 7

A capacitor in a single phase AC motor is to.

Answer 7

provide a phase shift

Question 8

The slip speed of an induction motor is.

Answer 8

stator speed-rotor speed

Question 9

An inductance/resistance motor is.

Answer 9

less efficient than a capacitance motor

Question 10

If a connection to a 3-phase AC motor is disconnected, the motor will.

Answer 10

continue to run

Question 11

The phases in supply to a 2 phase motor are electrically.

Answer 11

180 degrees apart from each other

Question 12

Calculate the speed of a 400 Hz, 4 pole machine.

Answer 12

12,000 rpm

Question 13

A capacitor in a single phase motor is to.

Answer 13

provide a phase shift

Question 14

Slip on a synchronous motor on start is.

Answer 14

100 %

Question 15

A shaded pole motor has shaded poles to.

Answer 15

create a rotating field

Question 16

In a 2 phase induction motor the control winding is fed with.

Answer 16

constant phase AC supply

Question 17

A 3 phase induction motor can be reversed by.

Answer 17

changing over any two phases

Question 18

The speed of an AC motor can be affected by the.

Answer 18

pairs of poles

Question 19

An AC motor which rotates at the same speed as the supply frequency is called.

Answer 19

a synchronous motor

Question 20

In a synchronous motor, when the motor is running the slip is.

Answer 20

0%

Question 21

In a two-phase induction motor there are.

Answer 21

4 poles

Question 22

The speed of a single phase induction motor is dependant on.

Answer 22

the number of pairs of poles

Question 23

Motor slip is.

Answer 23

the percentage of difference in speeds between the stator and rotor fields

Question 24

The principal characteristic of a synchronous motor is.

Answer 24

it rotates at a speed that is synchronised with the applied ac current

Question 25

A simple basic induction motor has.

Answer 25

poor starting torque, good running torque

Question 26

Which of the following applications would require a ‘continuously rated’ motor?.

Answer 26

Fuel pump motor

Question 27

A centrifugal speed switch is used.

Answer 27

to cut out the resistor/inductor circuit on an AC motor

Question 28

Disconnecting one of the phases from a 3-phase motor will cause the motor to.

Answer 28

run at the same speed

Question 29

The controlling phase on a two phase motor is of a.

Answer 29

variable amplitude

Question 30

The difference in speed between a synchronous motor’s rotor and stator is known as.

Answer 30

slip speed

Question 31

What is the purpose of the capacitor used in a single phase AC motor?.

Answer 31

Provides a high starting torque