The duration of sudden short-circuit test on a synchronous motor is usually about

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

While starting a synchronous motor by induction motor action, field winding is usually

A

connected to D.C. supply

B

short-circuited by low resistance

C

kept open-circuited

D

none of the above

A synchronous motor can be used as a synchronous capacitor when it is

A

under-loaded

B

over-loaded

C

under-excited

D

over-excited

A synchronous motor can develop synchronous torque

A

when under loaded

B

while over-excited

C

only at synchronous speed

D

below or above synchronous speed

The efficiency of a properly designed synchronous motor will usually fall in range

A

60 to 70%

B

75 to 80%

C

85 to 95%

D

99 to 99.5%

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

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because

A

synchronous motor has no slip

B

stator supply is not required to produce magnetic field

C

mechanical load on the rotor remains constant

D

synchronous motor has large airgap

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

A

stop

B

run as induction motor

C

function as static condenser

D

burn with dense smoke

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by

A

induction motor torque in field winding

B

induction motor torque in damper winding

C

eddy current and hysteresis torque in pole faces

D

reHetance motor torque due to saliency of the rotor

E

all of the above methods

In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will

A

Become unstable

B

Draw excessive armature current and may burn out

C

Fall out of synchronism and come to stand still

D

Run as induction motor

The duration of sudden short-circuit test on a synchronous motor is usually about

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