Electrical Synchronous Motor MCQ - Set 08 - ObjectiveBooks

Electrical Synchronous Motor MCQ - Set 08

Practice Test: Question Set - 08

1. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
    (A) Increase in both armature current and power factor angle
    (B) Increase in back e.m.f. but decrease in armature current
    (C) Increase in both armature current and power factor which is lagging
    (D) Increase in torque angle but decrease in back e.m.f.

2. The armature current of the synchronous motor has higher values for
    (A) High excitation only
    (B) Low excitation only
    (C) Both (A) and (B)
    (D) None of the above

3. In a synchronous motor, the maximum power developed depends on all of the following except
    (A) Rotor excitation
    (B) Maximum value of coupling angle
    (C) Direction of rotation
    (D) Supply voltage

4. Hunting in a synchronous motor cannot be due to
    (A) Windage friction
    (B) Variable load
    (C) Variable frequency
    (D) Variable supply voltage

5. Which of the following losses is not dissipated by the stator core surface in a synchronous motor?
    (A) Eddy current losses in the conductors
    (B) Iron losses in the stator
    (C) Copper losses in the slot portion of the conductors
    (D) Windage losses

6. The maximum power developed in a synchronous motor will depend on
    (A) The rotor excitation only
    (B) The supply voltage only
    (C) The rotor excitation and supply voltage both
    (D) The rotor excitation, supply voltage and maximum value of coupling angle (90°)

7. A synchronous motor can be started by
    (A) Pony motor
    (B) D.C. compound motor
    (C) Providing damper winding
    (D) Any of the above

8. The shaft of synchronous motor is made of
    (A) Mild steel
    (B) Chrome steel
    (C) Alnico
    (D) Stainless steel

9. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
    (A) Synchronous motor has no slip
    (B) Stator supply is not required to produce magnetic field
    (C) Mechanical load on the rotor remains constant
    (D) Synchronous motor has large air-gap

10. Power factor of a synchronous motor is unity when
    (A) The armature current is maximum
    (B) The armature current is minimum
    (C) The armature current is zero
    (D) None of the above

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