AC MOTORS

The back EMF of a synchronous motor depends on

• speed

• load

• load angle

• all of these

The oscillations in a synchronous motor can be damped out by

• maintaining constant excitation

• running the motor on leading power factors

• providing damper bars in the rotor pole faces

• All of these

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

• zero leading power factor

• unity power factor

• 0.707 lagging power factor

• 0.707 leading power factor

Hunting in a synchronous motor can be minimized by

• using damper bars

• using a flywheel

• designing the motor for adequate synchronizing power

• any of the above methods.

An over-excited synchronous motor takes

• leading current

• lagging current

• Both of these

• none of the above

The power developed by a synchronous motor will be maximum when the load angle is

• zero

• 45

• 90

• 145

A synchronous motor can be started by

• pony motor

• D.C. compound motor

• providing damper winding

• All of these

The reason for synchronous motors are generally not self-starting

• the direction of rotation is not fixed

• the direction of instantaneous torque reverses after half cycle

• starters cannot be used on these machines

• starting winding is not provided on the machines

In case of a 3 phase synchronous motor, maximum speed variation is

• 0.1

• 0.05

• 0.03

• 0

The slip of a synchronous motor is:

• zero

• positive

• negative

• cannot be determined without knowing the load