Chapter 19- AC motors

Starting of induction motor under reduce voltage will Reduce the starting torque Increase the starting torque Have no effect on the starting torque Increase the horsepower

Reduce starting torque

On a three phase motor, the stater windings are arranged to produce A rotating magnetic field An oscillating magnetic field Fluctuating magnetic field A stationary magnetic field

Rotating magnetic field

The synchronous speed of an induction motor refers to the speed of the Rotor Armature Rotating magnetic field Rotor flux

Rotor

Repultion motor is a three phase motor Single phase motor DC motor Universal motor

Single phase motor

Shaded pole motors can be used to drive Compressors Printing presses Small fans Pumps

Small fans

A squirrel cage rotor has windings that consist of Copper wire wound on a core similar to a DC shunt motor Copper bars placed in slots around the surface of a cylinder Projecting Poles similar to an AC alternator Either a or B

Copper bars placed in slots around the surface of a cylinder

High frequency motors are used to obtain Greater speeds then are available from 60 Hz Lower speed then are available from 60 Hz More torque per horsepower Greater horsepower

Greater speeds then or available from 60 Hz

The starting current of an induction motor is Equal to the full load current Less than a full load current Greater than the full load current 1/2 of the full load current

Greater than the full load current

The direction of rotation of the rotor of a three phase induction motor is determined by the Frequency Phase sequence Number of stator poles Number of phases

Phase sequence

A three phase ,two pole induction motor operating from the 60 Hz supply will produce a synchronous, speed in revolutions per minute, of 3600 1800 2400 1200

3,600 revolutions per min

Universal motor is designed to operate from An AC single phase supply A DC supply Both A and B A three phase supply

Both A and B

A polyphase synchronous motor requires Both AC and DC Two values of voltage Only AC Only DC

Both AC and DC

A synchronous motor is frequently used To improve the power factor To drive variable, speed loads To maintain a steady frequency None of the above

To maintain a steady frequency

The speed of a squirrel cage motor can be varied by Varying the voltage Using a specially manufactured motor with multiple winding connections Varying the current Varying the wattage

Usually a specially manufactured motor with multiple winding connections