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Synchronous Motors - section-1
Synchronous Motors - Section-2
  1. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is

    2. A.

     supplied with unbalanced voltage
    B.

     under-loaded
    C.

     over-loaded
    D.

     none of the above

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  2. As the load is applied to a synchronous motor, the motor takes more armature current because

    3. A.

     The increased load has to take more current
    B.

     The rotor by shifting its phase backward causes motor to take more current
    C.

     The back e.m.f. decreases causing an increase in motor current
    D.

     The rotor strengthens the rotating field causing more motor current

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  3. The power factor of a synchronous motor is better than that of induction motor because

    4. A.

     stator supply is relieved of responsibility of producing magnetic field
    B.

     mechanical load on the motor can be adjusted
    C.

     synchronous motor runs at synchronous speed
    D.

     synchronous motor has large air gap

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  4. An important advantage of a synchronous motor over wound round induction motor is that

    5. A.

     its power factor may be varied at will
    B.

     its speed is independent of supply frequency
    C.

     its speed may be controlled more easily
    D.

     none of the above

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  5. In case one phase of a three-phase synchronous motor is short-circuited the motor will

    6. A.

     not start
    B.

     run at 2/3 of synchronous speed
    C.

     run with excessive vibrations
    D.

     take less than the rated load

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  6. An over excited synchronous motor is used for

    7. A.

     Fluctuating loads
    B.

     Variable speed loads
    C.

     Low torque loads
    D.

     Power factor corrections

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  7. Riunting in a synchronous motor takes place

    8. A.

     When supply voltage fluctuates
    B.

     When load varies
    C.

     When power factor is unity
    D.

     Motor is under loaded

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  8. The rotor copper losses, in a synchronous motor, are met by

    9. A.

     d.c. source
    B.

     armature input
    C.

     motor input
    D.

     supply lines

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  9. For power factor correction, synchronous motors operate at

    10. A.

     no-load and greatly over-excited fields
    B.

     no-load and under-excited fields
    C.

     normal load with minimum excitation
    D.

     normal load with zero excitation

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  10. The size of a synchronous motor decreases with the increase in

    11. A.

     flux density
    B.

     horse power rating
    C.

     speed
    D.

     all of the above

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