For a D.C. shunt motor if the excitation is changed

A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will

A

remain same

B

go down

C

improve

D

none of the above

If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

A

This will make armature to take heavy current, possibly burning it

B

This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

C

Nothing will happen to motor

D

Motor will come to stop

If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens

A

Nothing will happen to the motor

B

This will make armature to take heavy current, possibly burning it

C

This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

D

Motor will run at very slow speed

A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

A

power factor as well as armature current will decrease

B

power factor as well as armature current will increase

C

power factor will increase but armature current will decrease

D

power factor will decrease and armature current will increase

If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will

A

Increase

B

Decrease

C

Remain same

D

Become zero

If the field of a D.C. shunt motor gets opened while motor is running

A

The speed of motor will be reduced %

B

The armature current will reduce

C

The motor will attain dangerously high speed 1

D

The motor will continue to run at constant speed

If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to

A

increase in both armature current and power factor angle

B

increase in back e.m.f. but decrease in armature current

C

increase in both armature current and power factor which is lagging

D

increase in torque angle but decrease in back e.m.f.

In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately

A

One-third

B

Twice

C

Thrice

D

Six times

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

A

will become more

B

will become less

C

will remain unchanged

D

none of the above.

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

A

become more

B

become less

C

remain constant

D

none of the above

For a D.C. shunt motor if the excitation is changed

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