GATE Synchronous Motor For Electrical Engineering

Test Preparation on GATE Synchronous Motor For Electrical Engineering

1.

Synchronous motors are generally not self-starting because

1the direction of rotation is not fixed
2the direction of instantaneous torque reverses after half cycle
3startes cannot be used on these machines
4starting winding is not provided on the machines

2.

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

1not start
2run at 2/3 of synchronous speed
3run with excessive vibrations
4take less than the rated load

3.

A pony motor is basically a

1small induction motor
2D.C. series motor
3D.C. shunt motor
4double winding A.C./D.C. motor

4.

An asynchronous motor can develop synchronous torque

1when under loaded
2while over-excited
3only at synchronous speed
4below or above synchronous speed

5.

A synchronous motor can be started by

1pony motor
2D.C. compound motor
3providing damper winding
4any of the above

6.

A three-phase synchronous motor will have

1no slip-rings
2one slip-ring
3two slip-rings
4three slip-rings

7.

Under which of the following conditions hunting of synchronous motor is likely to occur ?

1Periodic variation of load
2Over-excitation
3Over-loading for long periods
4Small and constant load

8.

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

1the motor stops
2it runs as a reluctance motor at the same speed
3it runs as a reluctance motor at a lower speed
4none of the above

9.

When V is the applied voltage, then the breakdown torque of a synchronous motor varies as

1V
2V312
3V2
41/V

10.

The power developed by a synchronous motor will be maximum when the load angle is

1zero
245?
390?
4120?

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