5. Study the following :  Theory of the induction motors (single and three phase).  Methods of speed control of induction motors.  Circuit diagram of equivalent of the induction motor.  Equations of the performance and curves of it.  Examples. Study the following :  Theory of the induction motors (single and three phase).  Methods of speed control of induction motors.  Circuit diagram of equivalent of the induction motor.  Equations of the performance and curves of it.  Examples.

8. Primarily, electric drives can be divided into two groups, dc drives and ac drives. Advantages and disadvantages of ac drives with respect to dc drives are as under : Advantages of ac drives (i)For the same rating, ac motor are lighter in weight as compared to dc motors. (ii)AC motor are less expensive as compared to equivalent dc motor. (iii)AC motor require low maintenance as compared to dc motor. (iv)AC motor can work in hazardous areas like chemical, petrochemical etc. whereas dc motor are unsuitable for such environments because of commutator sparking. Disadvantages of ac drives (i)Power converters for the control of ac motors are more complex. (ii)Power converters for ac drives more expensive. ( iii) power converters for ac drive generate harmonic in the supply system and load circuit. As result, ac motor get debated.

10. The stator winding are supply with balance three – phase AC voltage, which produce voltage in the rotor windings. It is possible to arrange the distribution of stator winding so that there is an effect of multiple poles, producing several cycle of magneto motive force (mmf) or field around the air gap.

11. Three –phase induction motor are more commonly employed in adjustable-speed drives than three–phase synchronous motors. Three–phase induction motor are of two type, squirrel-cage induction motors (SCIMs) and slip-ring (or wound-rotor)induction motors(SRIMs). Stator windings of both types carry three-phase winding. Rotor of SCIM is made of copper or aluminum bar short-circuited by two end rings. Rotor of SRIM carries three-phase winding connected to three slip rings on the rotor shaft. When 3-phase supply is connected to three-phase stator winding, rotating magnetic field is produce. The speed of this rotating field, called synchronous speed, is given by

14. X1X1 r1r1 XmXm V1V1 X2X2 E2E2 I1I1 I2I2 IeIe X1X1 r1r1 XmXm V1V1 X2X2 I2I2 IeIe I1I1 r1r1 r2r2 X1X1 X2X2

19. There are many ways to controlled on the speed of IM 1. Stator voltage control 2. Variable frequency control 3. Rotor resistance control 4. Slip energy recovery scheme We take the third way for example (Rotor voltage control ).

20. These resistors Rx are used to control motor starting and stopping anywhere from reduced voltage motors of low horsepower up to large motor applications such as materials handling, mine hoists, cranes etc.