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EEE :: Synchronous Motors

  1. The percentage slip in case of a synchronous motor is

  2. A.

     1%

    B.

     100%

    C.

     0.5%

    D.

     zero

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  3. The maximum speed variation in a 3-phase synchronous motor is

  4. A.

     10 per cent

    B.

     6 per cent

    C.

     4 per cent

    D.

     2. per cent

    E.

     zero

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  5. The ratio of starting torque to running torque in a synchronous motor is

  6. A.

     zero

    B.

     one

    C.

     two

    D.

     infinity

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  7. When load on an over-excited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is

  8. A.

     more

    B.

     less

    C.

     equal

    D.

     twice

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  9. A synchronous motor can be made self starting by providing

  10. A.

     Damper winding on rotor poles

    B.

     Damper winding on stator

    C.

     Damper winding on stator as well as rotor poles

    D.

     None of the above

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  11. A synchronous machine with large air gap has

  12. A.

     a higher value of stability limit

    B.

     a small value of inherent regulation

    C.

     a higher synchronizing power which makes the machine less sensitive to load variations

    D.

     all of the above

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  13. In a synchronous motor, the maximum power developed depends on all of the following except

  14. A.

     rotor excitation

    B.

     maximum value of coupling angle

    C.

     direction of rotation

    D.

     supply voltage

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  15. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?

  16. A.

     By changing the supply frequency

    B.

     By interchanging any two phases

    C.

     By changing the applied voltage

    D.

     By changing the load

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  17. Hunting in a synchronous motor cannot be due to

  18. A.

     windage friction

    B.

     variable load

    C.

     variable frequency

    D.

     variable supply voltage

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  19. The duration of sudden short-circuit test on a synchronous motor is usually about

  20. A.

     one hour

    B.

     one minute

    C.

     one second

    D.

     none of the above

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