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EEE :: Synchronous Motors

  1. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?

  2. A.

     Stator flux

    B.

     Pull in torque

    C.

     Both (A) and (B)

    D.

     None of the above


  3. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected

  4. A.

     the motor stops

    B.

     it runs as a reluctance motor at the same speed

    C.

     it runs as a reluctance motor at a lower speed

    D.

     none of the above


  5. The effect of increasing the load on a synchronous motor running with normal excitation is to

  6. A.

     decrease both armature current and power factor

    B.

     decrease armature current but increase power factor

    C.

     increase armature current but decrease power factor

    D.

     increase both its armature current and power factor


  7. Synchronous motor always runs at

  8. A.

     the synchronous speed

    B.

     less than synchronous speed

    C.

     more than synchronous speed

    D.

     none of the above


  9. A synchronous motor can operate at

  10. A.

     lagging power factor only

    B.

     leading power factor only

    C.

     unity power factor only

    D.

     lagging, leading and unity power factors


  11. A pony motor is basically a

  12. A.

     small induction motor

    B.

     D.C. series motor

    C.

     D.C. shunt motor

    D.

     double winding A.C./D.C. motor


  13. The maximum power developed in a synchronous motor will depend on

  14. A.

     the rotor excitation only

    B.

     the supply voltage only

    C.

     the rotor excitation and supply volt-age both

    D.

     the rotor excitation, supply voltage and maximum value of coupling angle (90°)


  15. Armature of a synchronous machine is

  16. A.

     Of reducing number of slip rings on the rotor

    B.

     Armature is associated with large power as compared to the field circuits

    C.

     Of difficulty of providing high voltage insulation on rotor

    D.

     All of the above reasons


  17. Synchronsizingpower of a synchronous machine is

  18. A.

     direcly proportional to the synchronous reactance

    B.

     inversely proportional to the synchronous reactance

    C.

     equal to the synchronous reactance

    D.

     none of the above


  19. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will

  20. A.

     remain same

    B.

     go down

    C.

     improve

    D.

     none of the above