SYNCHRONOUS MOTORS QUIZ

Small synchronous motors are started by _______

None of the listed here

Pony motor

Variable frequency source

Damper winding

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The back e.m.f. of a synchronous motor depends on

load

All of these

speed

load angle

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In a synchronous motor, the maximum power developed depends on all of the following except

supply voltage

maximum value of coupling angle

direction of rotation

rotor excitation

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A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have

no change of power factor

leading power factor with under-excitation

lagging power factor with over-excitation

leading power factor with over-excitation

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The power factor correction capability of a loaded synchronous motor _____ with the increases in mechanical load.

None of the listed here

Remains unchanged

Decreases

Increases

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Synchronous motors are generally used in application requiring _______

Infrequent starting

Frequent stopping

Sudden application of heavy loads

Variable speed

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The mechanical power developed by a synchronous motor is independent of _________.

Speed

Applied stator voltage

Field excitation

Torque angle

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A synchronous motor runs at speed ranging from ______

3600 to 6000 rpm

None of the listed here

150 to 1800 rpm

1800 to 3600 rpm

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A synchronous motor is cheaper than 3-phase induction motor for _____

High speed, high output

Low speed, high output

High speed, low output

None of the listed here

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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

eddy current and hysteresis torque in pole faces

induction motor torque in damper winding

All of the listed here

induction motor torque in field winding

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