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Synchronous Motors

Study 122 Electrical Engineering MCQs with correct answers and explanations.

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1Electrical EngineeringMedium

The synchronous motor is not inherently self-starting because________?

Aa rotating magnetic field does not have enough poles

Bthe force required to accelerate the rotor to the synchronous speed in an instant is absent

Cthe rotating magnetic field is produced by only 50 Hz frequency currents

Dthe starting device to accelerate the rotor to near synchronous speed is absent

Correct answer

B. the force required to accelerate the rotor to the synchronous speed in an instant is absent

Explanation

The correct answer is the force required to accelerate the rotor to the synchronous speed in an instant is absent.

2Electrical EngineeringMedium

For V-curves for a synchronous motor the graph is drawn between:________?

Aarmature current and power factor

Bterminal voltage and load factor

Cfield current and armature current

Dpower factor and field current

Correct answer

C. field current and armature current

Explanation

The correct answer is field current and armature current.

3Electrical EngineeringMedium

When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop________?

Asynchronous motor torque

Bd.c. motor toque

Cinduction generator torque

Dinductor motor torque

Enone of the above

Correct answer

C. induction generator torque

Explanation

The correct answer is induction generator torque.

4Electrical EngineeringMedium

When the field of a synchronous motor is under-excited, the power factor will be________?

Azero

Bunity

Clagging

Dleading

Correct answer

C. lagging

Explanation

The correct answer is lagging.

5Electrical EngineeringMedium

In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately

Aone-third

Bsix times

Cnine times

Dthrice

Etwice

Correct answer

D. thrice

Explanation

The correct answer is thrice.

6Electrical EngineeringMedium

In a synchronous motor, the breakdown torque is________?

Ainversely proportional to applied voltage

Bdirectly proportional to the square of the applied voltage

Cdirectly proportional to applied voltage

Dnone of the above

Correct answer

C. directly proportional to applied voltage

Explanation

The correct answer is directly proportional to applied voltage.

7Electrical EngineeringMedium

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by________?

Ainduction motor torque in damper winding

Binduction motor torque in field winding

Call of the above methods

DreHetance motor torque due to saliency of the rotor

Eeddy current and hysteresis torque in pole faces

Correct answer

C. all of the above methods

Explanation

The correct answer is all of the above methods.

8Electrical EngineeringMedium

A synchronous motor will always stop when:________?

Aexcitation winding gets disconnected

Bload in motor varies

Csupply voltage frequency changes

Dsupply voltage fluctuates

Correct answer

A. excitation winding gets disconnected

Explanation

The correct answer is excitation winding gets disconnected.

9Electrical EngineeringMedium

While starting a synchronous motor by induction motor action, field winding is usually________?

Akept open-circuited

Bconnected to D.C. supply

Cshort-circuited by low resistance

Dnone of the above

Correct answer

C. short-circuited by low resistance

Explanation

The correct answer is short-circuited by low resistance.

10Electrical EngineeringMedium

In which of the following motors the stator and rotor fields rotate simultaneously?

ASynchronous motor

BD.C. motor

CUniversal motor

DInduction motor

EReluctance motor

Correct answer

A. Synchronous motor

Explanation

The correct answer is Synchronous motor.

The synchronous motor is not inherently self-starting because________?

Aa rotating magnetic field does not have enough poles

Bthe force required to accelerate the rotor to the synchronous speed in an instant is absent

Cthe rotating magnetic field is produced by only 50 Hz frequency currents

Dthe starting device to accelerate the rotor to near synchronous speed is absent

Correct answer

B. the force required to accelerate the rotor to the synchronous speed in an instant is absent

Explanation

The correct answer is the force required to accelerate the rotor to the synchronous speed in an instant is absent.

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by________?

Ainduction motor torque in damper winding

Binduction motor torque in field winding

Call of the above methods

DreHetance motor torque due to saliency of the rotor

Eeddy current and hysteresis torque in pole faces

Correct answer

C. all of the above methods

Explanation

The correct answer is all of the above methods.