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EEE :: Synchronous Motors

  1. Power factor of a synchronous motor is unity when

  2. 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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  3. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be

  4. A.

     3000 r.p.m.

    B.

     1500 r.p.m.

    C.

     750 r.p.m.

    D.

     none of the above

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  5. Which of the following motors is non-self starting ?

  6. A.

     D.C. series motor

    B.

     synchronous motor

    C.

     Squirrel cage induction motor

    D.

     Wound round induction motor

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  7. Which of the following losses, in a synchronous motor, does not vary with load?

  8. A.

     Windage loss

    B.

     Copper losses

    C.

     Any of the above

    D.

     None of the above

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  9. Stability of a synchronous machine

  10. A.

     decreases with increase in its excitation

    B.

     increases with increase in its excitation

    C.

     remains unaffected with increase in excitation

    D.

     any of the above

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  11. Which of the following methods is used to start a synchronous motor ?

  12. A.

     Damper winding

    B.

     Star-delta starter

    C.

     Damper winding in conjunction with star-delta starter

    D.

     Resistance starter in the armature circuit

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  13. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?

  14. A.

     Phase to phase winding resistance

    B.

     Stator winding to earthed frame

    C.

     Rotor winding to earthed shaft

    D.

     All of the above

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  15. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?

  16. 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

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  17. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of

  18. A.

     zero degree

    B.

     two degrees

    C.

     five degrees

    D.

     ten degrees

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  19. A synchronous motor working at leading power factor can be used as

  20. A.

     voltage booster

    B.

     phase advancer

    C.

     noise generator

    D.

     mechanical synchronizer

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