AC Motor Test

Question 1

What is the principle of operation of all three phase motors?

Answer 1

Rotor flux caused by current induced by flux of stator

Question 2

The core of the stator and the rotor are laminated to reduce the effect of hysteresis.

Answer 2

False

Question 3

At 10% drop in supply frequency or clause the synchronous speed of a squirrel cage induction motor to blank

Answer 3

Decelerate at a linear rate

Question 4

What type of current flow produces flux in the rotor circuit of a three phase induction motor?

Answer 4

Induced AC current

Question 5

What is the synchronous speed of a three phase 5 hp 240 V 12 amp 60 Hz for pole motor?

Answer 5

1800 RPM

Question 6

A three phase induction motor will always have a rotor speed that is blank the stator synchronous speed

Answer 6

Less than

Question 7

Three phase 600 V 60 Hz four pole motor will induce four poles on it’s rotor

Answer 7

True

Question 8

How many poles must the stator of a three phase 600 V 60 Hz 10 hp 795 RPM motor contain?

Answer 8

Eight

Question 9

Using compressed air to clean dust from inside the motor is preferred maintenance procedure.

Answer 9

False

Question 10

What must be the duty cycle of the field resistors of a wound rotor motor shown below?

Answer 10

Continuous duty

Question 11

How do we reverse the direction of the wound rotor motor shown above?

Answer 11

Interchange any two stator leads

Question 12

Using a wound rotor motor what is the common position of the speed controller rheostats at start up?

Answer 12

Maximum resistance

Question 13

If we connected jumpers across the slip rings of the unloaded motor from question 12 what would be the starting characteristics of the motor?

Answer 13

Low torque high speed

Question 14

Leaving the starting resistors in the rotor circuit improve the running efficiency of the wound rotor motor circuit

Answer 14

False

Question 15

How does the wound rotor motor minimize a loss of starting torque?

Answer 15

By having a rotor power factor closer to unity

Question 16

As the wound rotor motor accelerates which of the following is true of the rotor circuit?

Answer 16

The rotor impedance is decreasing

Question 17

What current will flow in the amortisseur winding of the synchronous motor?

Answer 17

Induced AC current

Question 18

How is the field excitation supplied to a synchronous motor?

Answer 18

From a DC source

Question 19

What are the two main components of a brushless exciter for a synchronous motor?

Answer 19

Alternator and rectifier

Question 20

How is the excitation current applied to the road or in the case of synchronous motors with external converters?

Answer 20

With brushes on slip rings

Question 21

What type of excitation is needed for a synchronous condenser?

Answer 21

Over excitation