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EEE :: Synchronous Motors

  1. A synchronous motor will always stop when

  2. A.

     supply voltage fluctuates

    B.

     load in motor varies

    C.

     excitation winding gets disconnected

    D.

     supply voltage frequency changes

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  3. Which of the following motors will be used in electric clocks ?

  4. A.

     D.C. shunt motor

    B.

     D.C. series motor

    C.

     A.C. induction motor

    D.

     A.C. synchronous motor

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  5. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way

  6. A.

     augments it directly

    B.

     directly opposes it

    C.

     cross-magnetises it

    D.

     none of the above

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  7. In a synchronous motor, damper windings are provided on

  8. A.

     stator frame

    B.

     rotor shaft

    C.

     pole faces

    D.

     none of the above

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  9. In a synchronous motor, the damping winding is generally used to

  10. A.

     prevent hunting and provide the starting torque

    B.

     reduce the eddy currents

    C.

     provide starting torque only

    D.

     reduce noise level

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

  12. 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 airgap

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  13. Under which of the following conditions hunting of synchronous motor is likely to occur ?

  14. A.

     Periodic variation of load

    B.

     Over-excitation

    C.

     Over-loading for long periods

    D.

     Small and constant load

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  15. The torque angle, in a synchronous motor, is the angle between

  16. A.

     the supply voltage and the back e.m.f.

    B.

     magnetising current and back e.m.f.

    C.

     the rotating stator flux and rotor poles

    D.

     none of the above

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  17. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

  18. A.

     Speed of the motor is reduced

    B.

     Power factor is decreased

    C.

     Eb (back e.m.f.) becomes less than V (applied voltage)

    D.

     Er (net resultant voltage) in armature is increased

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  19. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

  20. A.

     stop

    B.

     run as induction motor

    C.

     function as static condenser

    D.

     burn with dense smoke

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