Synchronous motors Archives

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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