2.7 EM

In a three-phase induction motor, the rotating magnetic field is produced by:

• a) Stator windings

• b) Rotor windings

• c) Stator and rotor windings

• d) Permanent magnets

The slip of a three-phase induction motor is defined as:

• a) The difference between synchronous speed and rotor speed

• b) The difference between stator frequency and rotor frequency

• c) The difference between input power and output power

• d) The difference between rotor resistance and rotor reactance

The torque in a three-phase induction motor is directly proportional to:

• a) Slip

• b) Stator voltage

• c) Rotor resistance

• d) Rotor reactance

The type of rotor used in a squirrel cage induction motor is characterized by:

• a) Laminated iron cores

• b) Copper or aluminum bars shorted at the ends

• c) Wound rotor with slip rings

• d) Permanent magnets

The starting of a three-phase induction motor can be improved by:

• a) Decreasing the stator voltage

• b) Increasing the rotor resistance

• c) Using a soft starter

• d) Increasing the slip