Synchronous motors

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

voltage booster
phase advancer
noise generator
mechanical synchronizer

Detailed SolutionA synchronous motor working at leading power factor can be used as

2. A three-phase synchronous motor will have

no slip-rings
one slip-ring
two slip-rings
three slip-rings

Detailed SolutionA three-phase synchronous motor will have

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

flux density
horse power rating
speed
all of the above

Detailed SolutionThe size of a synchronous motor decreases with the increase in

4. In a synchronous motor, damper windings are provided on

stator frame
rotor shaft
pole faces
none of the above

Detailed SolutionIn a synchronous motor, damper windings are provided on

5. If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

will become more
will become less
will remain unchanged
none of the above.

Detailed SolutionIf in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

6. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as

pull-up torque
pull-in torque
pull-out torque
none of the above

Detailed SolutionThe maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as

7. Synchronous motor always runs at

the synchronous speed
less than synchronous speed
more than synchronous speed
none of the above

Detailed SolutionSynchronous motor always runs at

8. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

the stator current will be zero
the stator current will be very small
the stator current will be very high
the back e.m.f. will be more than the supply voltage

Detailed SolutionIf the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

9. For power factor correction, synchronous motors operate at

no-load and greatly over-excited fields
no-load and under-excited fields
normal load with minimum excitation
normal load with zero excitation

Detailed SolutionFor power factor correction, synchronous motors operate at

10. The synchronous motor is not inherently self-starting because

the force required to accelerate the rotor to the synchronous speed in an instant is absent
the starting device to accelerate the rotor to near synchronous speed is absent
a rotating magnetic field does not have enough poles
the rotating magnetic field is produced by only 50 Hz frequency currents

Detailed SolutionThe synchronous motor is not inherently self-starting because

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