Synchronous Motor Objective Questions - Set 02 - ObjectiveBooks

# Practice Test: Question Set - 02

1. The net armature voltage of a synchronous motor is equal to the
(A) Vector sum of Eb and V
(B) Arithmetic sum of Eb and V
(C) Arithmetic difference of Eb and V
(D) Vector difference of Eh and V

2. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value?
(A) By changing the supply frequency
(B) By interchanging any two phases
(C) By changing the applied voltage

3. If the field of a synchronous motor is under-excited, the power factor will be
(A) Zero
(B) Unity
(C) Lagging

4. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
(A) Pull-up torque
(B) Pull-in torque
(C) Pullout torque
(D) None of the above

5. The coupling angle or load angle of synchronous motor is defined as the angle between the
(A) Rotor and stator teeth
(B) Rotor and the stator poles of opposite polarity
(C) Rotor and the stator poles of the same polarity
(D) None of the above

6. Synchronous motors are generally not self-starting because
(A) The direction of rotation is not fixed
(B) The direction of instantaneous torque reverses after half cycle
(C) Starters cannot be used on these machines
(D) Starting winding is not provided on the machines

7. The power developed by a synchronous motor will be maximum when the load angle is
(A) Zero
(B) 45°
(C) 90°
(D) 120°

8. The working of a synchronous motor is similar to
(A) Gear train arrangement
(B) Transmission of mechanical power by shaft
(C) Distribution transformer
(D) Turbine

9. The oscillations in a synchronous motor can be damped out by
(A) Maintaining constant excitation
(B) Running the motor on leading power factors
(C) Providing damper bars in the rotor pole faces
(D) Oscillations cannot be damped

10. When load on an overexcited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is
(A) More
(B) Less
(C) Equal
(D) Twice

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