Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?

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

A

pull-up torque

B

pull-in torque

C

pull-out torque

D

none of the above

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

The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as

A

slip torque

B

pull-out torque

C

breaking torque

D

synchronising torque

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

The length of a rectangular field F is 3 km greater than the side of a square field M , and the width of field F is 3 km less then the side of field M. If the area of field M is m2 square km, what is the area of field F?

A

m2 +6

B

6

C

m2 - 6

D

m2 +9

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

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

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

As the load is applied to a synchronous motor, the motor takes more armature current because

A

The increased load has to take more current

B

The rotor by shifting its phase backward causes motor to take more current

C

The back e.m.f. decreases causing an increase in motor current

D

The rotor strengthens the rotating field causing more motor current

Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?

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