In _________ method of staging three phase induction motors the starting voltage is not reduced.

For three-phase induction motors which of the following is the least efficient method of speed control?

A

Cascade control

B

Pole changing

C

Rheostat control

D

Combination of cascade and pole changing

In three-phase squirrel-cage induction motors

A

Rotor conductor ends are short-circuited through slip rings

B

Rotor conductors are short-circuited through end rings

C

Rotor conductors are kept open

D

Rotor conductors are connected to insulation

In three-phase induction motors sometimes copper bars are placed deep in the rotor to

A

Improve starting torque

B

Reduce copper losses

C

Improve efficiency

D

Improve power factor

DOL starting of induction motors is usually restricted to

A

Low horsepower motors

B

Variable speed motors

C

High horsepower motors

D

High speed motors

In squirrel cage induction motors which of the following methods of starting cannot be used?

A

Resistance in rotor circuit

B

Resistance in stator circuit

C

Autotransformer starting

D

Star-delta starting

__________ method of starting a three phase induction motor needs six terminals.

A

Star-delta

B

Resistance starting

C

Autotransformer

D

None of the above

Which of the following single-phase induction motors is generally used in time phonographs?

A

Resistance start

B

Capacitor start capacitor run

C

Shaded pole

D

Universal

Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors?

A

Low cost

B

Wide speed range

C

Stability

D

High starting torque

The starting torque of a three phase induction motor can be increased by

A

Increasing slip

B

Increasing current

C

Both (A) and (B)

D

None of the above

Which of the following single-phase motors has relatively poor starting torque ?

A

Universal motor

B

Repulsion motor

C

Capacitor motor

D

All single phase motors have zero starting torque

In _________ method of staging three phase induction motors the starting voltage is not reduced.

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