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Synchronous Motors

Study 122 Electrical Engineering MCQs with correct answers and explanations.

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71Electrical EngineeringMedium

A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

Apower factor as well as armature current will increase

Bpower factor as well as armature current will decrease

Cpower factor will decrease and armature current will increase

Dpower factor will increase but armature current will decrease

Correct answer

C. power factor will decrease and armature current will increase

Explanation

The correct answer is power factor will decrease and armature current will increase.

72Electrical EngineeringMedium

Hunting in a synchronous motor cannot be due to________?

Avariable load

Bwindage friction

Cvariable frequency

Dvariable supply voltage

Correct answer

B. windage friction

Explanation

The correct answer is windage friction.

73Electrical EngineeringMedium

Which of the following methods is used to start a synchronous motor?

ADamper winding

BResistance starter in the armature circuit

CStar-delta starter

DDamper winding in conjunction with star-delta starter

Correct answer

D. Damper winding in conjunction with star-delta starter

Explanation

The correct answer is Damper winding in conjunction with star-delta starter.

74Electrical EngineeringMedium

The armature current of the synchronous motor has higher values for________?

Anone of the above

Bboth A. and (b)

Clow excitation only

Dhigh excitation only

Correct answer

B. both A. and (b)

Explanation

The correct answer is both A. and (b).

75Electrical EngineeringMedium

The maximum speed variation in a 3-phase synchronous motor is________?

A4 per cent

B2. per cent

Czero

D6 per cent

E10 per cent

Correct answer

C. zero

Explanation

The correct answer is zero.

76Electrical EngineeringMedium

Slip-rings in a synchronous motor carry________?

Ano current

Bdirect current

Calternating current

Dall of the above

Correct answer

B. direct current

Explanation

The correct answer is direct current.

77Electrical EngineeringMedium

In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on________?

Anone of the above

Bboth the speed and rotor flux

Cload on the motor

Dd.c. excitation only

Correct answer

D. d.c. excitation only

Explanation

The correct answer is d.c. excitation only.

78Electrical EngineeringMedium

The back e.m.f. of a synchronous motor depends on________?

Aload

Bspeed

Cload angle

Dall of the above

Correct answer

C. load angle

Explanation

The correct answer is load angle.

79Electrical EngineeringMedium

A synchronous motor can be used as a synchronous capacitor when it is________?

Aunder-loaded

Bover-loaded

Cover-excited

Dunder-excited

Correct answer

C. over-excited

Explanation

The correct answer is over-excited.

80Electrical EngineeringMedium

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

Astator supply is not required to produce magnetic field

Bsynchronous motor has no slip

Cmechanical load on the rotor remains constant

Dsynchronous motor has large airgap

Correct answer

A. stator supply is not required to produce magnetic field

Explanation

The correct answer is stator supply is not required to produce magnetic field.

A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

Apower factor as well as armature current will increase

Bpower factor as well as armature current will decrease

Cpower factor will decrease and armature current will increase

Dpower factor will increase but armature current will decrease

Correct answer

C. power factor will decrease and armature current will increase

Explanation

The correct answer is power factor will decrease and armature current will increase.

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

Astator supply is not required to produce magnetic field

Bsynchronous motor has no slip

Cmechanical load on the rotor remains constant

Dsynchronous motor has large airgap

Correct answer

A. stator supply is not required to produce magnetic field

Explanation

The correct answer is stator supply is not required to produce magnetic field.