Synchronous Motor MCQs with Answers

Synchronous Motor MCQs with answers: Following Multiple Choice Questions (MCQs) are based on “Synchronous Motor”. Specifically, following topics are included.

Topics: Construction, working principle, starting methods, effect of load, hunting, V-curve, synchronous condenser and applications of synchronous motors.

This syllabus is related with the subject Electrical Machines or Basic Electrical Engineering. This topic is mostly beneficial in the field of Electronics, Electrical and Mechanical Engineering.

These MCQs will be useful in various competitive examinations, entrance examinations, oral examination (Viva voce), certifications and interviews.

MCQ on Synchronous Motor

Que.1An electric motor in which both the rotor and stator fields rotates with the same speed is called __________ motor.
  1. d.c.
  2. servo
  3. synchronous
  4. stepper

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Option 3: synchronous

Que.2The direction of rotation of a synchronous motor can be reversed by reversing
  1. current to the field winding
  2. supply phase sequence
  3. polarity of rotor poles
  4. none of the above

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Option 2: supply phase sequence

Que.3In a synchronous motor, the magnitude of stator back e.m.f. depends on
  1. speed of the motor
  2. load on the motor
  3. both the speed and rotor flux
  4. d.c. excitation only

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Option 4: d.c. excitation only

Que.4Damper winding is provided in synchronous motor to
  1. stabilize rotor motion
  2. suppress rotor oscillations
  3. develop necessary starting torque
  4. both (ii) and (iii)

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Option 4: both (ii) and (iii)

Que.5The V-curves of a synchronous motor show relationship between
  1. field current and armature current.
  2. excitation current and back e.m.f.
  3. field current and supply voltage.
  4. armature current and supply voltage.

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Option 1: field current and armature current.

Que.6The angle between the synchronously-rotating stator flux and rotor poles of a synchronous motor is called _______ angle.
  1. short
  2. power factor
  3. slip
  4. torque

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Option 4: torque

Que.7The maximum value of torque angle a in a synchronous motor is ___.
  1. 45O
  2. less than 60O
  3. between 45O and 90O
  4. 90O

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Option 4: 90O

Que.8 Which of the following is most commonly used technique for starting synchronous motor?
  1. Using an induction motor
  2. By using a dc machine
  3. Using damper windings
  4. By using slip ring induction motor

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Option 3: Using damper windings

Que.9 Identify the correct statement/s.
i. When a synchronous motor is used for driving a varying load then the condition is called Hunting.
ii. Hunting may also be caused if supply frequency is pulsating.
  1. Only statement (i) is correct
  2. Both statements are correct
  3. Only statement (ii) is correct
  4. Both statements are wrong.

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Option 2: Both statements are correct

Causes of Hunting in Synchronous Motor
1. Sudden change in load.
2. Sudden change in field current.
3. A load containing harmonic torque.
4. Fault in supply system.
Que.10 Which of the following is an application of synchronous motor?
  1. Synchronous capacitor
  2. Voltage regulation
  3. Constant speed applications
  4. All of the above

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Option 4: All of the above

Que.11 If the field of a synchronous motor is under excited, the power factor will be _____.
  1. zero
  2. lagging
  3. leading
  4. unity

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Option 2: lagging

Que.12 When load on a normally-excited synchronous motor is increased, its power factor tends to
  1. remain unchanged
  2. become increasingly lagging
  3. become increasingly leading
  4. approach unity

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Option 2: become increasingly lagging

Que.13 Synchronous condenser is
  1. a static capacitor bank
  2. an over-excited synchronous motor driving mechanical load
  3. an over-excited synchronous motor running at no-load
  4. none of the above

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Option 3: an over-excited synchronous motor running at no-load

Que.14 Consider the following statements when using a synchronous motor as synchronous capacitor.
i. The main advantage of using synchronous motor is that the improvement of power factor is smooth.
ii. Another advantage of synchronous condenser is that the system is silent.
  1. Only statement (i) is correct
  2. Both statements are correct
  3. Both statements are wrong
  4. Only statement (ii) is correct

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Option 1: Only statement (i) is correct

Disadvantage of Synchronous condensor
The system is not silent since the synchronous motor has to rotate continuously.
Que.15In a synchronous machine when the rotor speed becomes more than the synchronous speed during hunting, the damping bars develop
  1. synchronous motor torque
  2. d.c. motor torque
  3. induction motor torque
  4. induction generator torque

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Option 4: induction generator torque

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