SYNCHRONOUS MOTORS QUIZ

The magnitude of field flux in a 3-phase synchronous motor

Remains constant at all loads

Varies with the load

Varies with power factor

Varies with speed

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A synchronous motor runs at only one speed because it ______

Is a doubly fed machine

Has a damper winding

Has no losses

None of the listed here

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An over excited synchronous motor is used for

Fluctuating loads

Low torque loads

Power factor corrections

Variable speed loads

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In a 3-phase synchronous motor, the negative phase sequence exists when the motor is

supplied with unbalanced voltage

None of these

over-loaded

under-loaded

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

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

The rotor strengthens the rotating field causing more motor current

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

The increased load has to take more current

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

None of these

one minute

one hour

one second

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The minimum armature current of the synchronous motor corresponds to operation at

0.707 power factor lagging

unity power factor

zero power factor leading

0.707 power factor leading

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While running, a synchronous motor is compelled to run at synchronous speed because of _______

Magnetic locking between stator and rotor poles

Damper winding in its pole faces

Compulsion due to lenz's law

Induced emf in rotor field winding by stator flux

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Hunting in a synchronous motor cannot be due to

variable supply voltage

variable frequency

windage friction

variable load

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In a synchronous motor, the magnitude of stator back emf depends on _____

Dc excitation only

Load on the motor

Both the speed and rotor flux

Speed of the rotor

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