Learning outcomes
       By the end of this module, students will be able to:
       Unit 11.1: three-phase induction motors
        •Explain the operation of a three-phase induction motor
        •Describe and explain the operating characteristics of a three-phase squirrel-cage 
        and wound-rotor motor
        •Calculate the synchronous speed and slip of an induction motor
        •List losses that occur in an induction motor
        •List the factors affecting the performance of induction motors
        •Unit 11.2: Single-phase induction motors
        •draw and explain, with the aid of circuit diagrams, the operation of single-phase 
        AC motors.
        •Sketch the typical torque-speed characteristics of the AC motors in the range.
     Operating principles of three-phase AC induction 
     motors
     •When a three-phase stator windings of induction motor are fed by a 
      three-phase supply, a magnetic flux of constant magnitude, but 
      rotating at synchronous speed is set up. The flux passes through the 
      air-gap, sweeps past the rotor surface and so cuts the rotor conductors 
      which as yet, are stationary. Due to the relative speed between the 
      rotating flux and stationary rotor conductors, emf is induced in the 
      latter and thus current starts flowing through the rotor conductors and 
      produces a torque which tends to move the rotor in the same direction 
      as the rotating fields.
     Parts of three-phase induction motor are:
     •The stator
     •The rotor
     •The end shield supporting the bearings.
     •The stator
     - The main function of a stator is to produce the magnetic flux
     - It is the stationary electrical part of the motor.
     - The stator core is made up of several hundred thin laminations.
     •The rotor
     - Is the rotating part of the electromagnetic circuit.
     - The rotor consists of a stack of steel laminations with evenly spaced 
      conductor bars around the circumference.
     - The rotor core is formed by the stacked laminations.
     •The two types of rotor motors
     - A squirrel-cage rotor motor
     - A wound-rotor motor
     •Losses that occur in an induction motor
     - Core losses
     - Mechanical losses
     •Factors affecting the performance of induction motors
     - Supply voltage
     - Loading
     - Line frequency
     - Phasing
     •Tests on induction motors
     - no-load or open-circuit test
     - Blocked rotor or short-circuit test
        Unit 11.2: Single-phase induction 
        motors
        •Operating principles of single-phase induction motor
        The moving magnetic field is produced in a single-phase motor by simulating the effect of 
        two-phase induction motor.
        •Types of single-phase induction motors (page 221 – 228)
        - capacitor-start capacitor-run motors
        - Permanent-capacitor motors
        - Capacitor-start induction-run motors
        - Resistance-start induction-run motors
        - Induction-start induction-run motors
        - Universal motors
        - Shaded-pole motors