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EEE :: Synchronous Motors

  1. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by

  2. A.

     induction motor torque in field winding

    B.

     induction motor torque in damper winding

    C.

     eddy current and hysteresis torque in pole faces

    D.

     reHetance motor torque due to saliency of the rotor

    E.

     all of the above methods

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  3. If one-phase of a 3-phase synchronous motor is short-circuited, motor

  4. A.

     will refuse to start

    B.

     will overheat in spots

    C.

     will not come upto speed

    D.

     will fail to pull into step

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  5. The net armature voltage of a synchronous motor is equal to the

  6. 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

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  7. The back e.m.f. of a synchronous motor depends on

  8. A.

     speed

    B.

     load

    C.

     load angle

    D.

     all of the above

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  9. The back e.m.f. in the stator of a synchronous motor depends on

  10. A.

     number of poles

    B.

     flux density

    C.

     rotor speed

    D.

     rotor excitation

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  11. The shaft of synchronous motor is made of

  12. A.

     mild steel

    B.

     chrome steel

    C.

     alnico

    D.

     stainless steel

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  13. A synchronous motor can develop synchronous torque

  14. A.

     when under loaded

    B.

     while over-excited

    C.

     only at synchronous speed

    D.

     below or above synchronous speed

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  15. When the field of a synchronous motor is under-excited, the power factor will be

  16. A.

     leading

    B.

     lagging

    C.

     unity

    D.

     zero

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  17. The induced e.m.f. in a synchronous motor working on leading power factor will be

  18. A.

     more than the supply voltage

    B.

     less than the supply voltage

    C.

     equal to the supply voltage

    D.

     none of the above

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  19. If the field of a synchronous motor is underexcited, the power factor will be

  20. A.

     zero

    B.

     unity

    C.

     lagging

    D.

     leading

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