- Three-phase induction motors are commonly used in industry due to their simple and rugged design, low cost, easy maintenance, and ability to operate at a constant speed from no load to full load. However, they require a variable frequency drive for optimal variable speed control. - An induction motor has two main parts - a stationary stator and a revolving rotor. The stator contains windings and the rotor comes in either a squirrel cage or wound rotor design. - The motor operates based on electromagnetic induction between the stator and rotor magnetic fields. An equivalent circuit model and diagrams of power flow help explain the motor's operation and torque-speed characteristics. The maximum torque is determined by a formula involving slip

1. Induction Motors
- Mr. V. S. Wadkar
- Assistant Professor,
- Department of Electrical Engineering,
- SITCOE

2. INTRODUCTION
 Three-phase induction motors are the most
common and frequently encountered machines in
industry
 simple design, rugged, low-price, easy maintenance
 wide range of power ratings: fractional horsepower to 10
MW
 run essentially as constant speed from zero to full load
 speed is power source frequency dependent
 not easy to have variable speed control
 requires a variable-frequency power-electronic drive for
optimal speed control

3. CONSTRUCTION
 An induction motor has two main parts
 Stationary Stator
 consisting of a steel frame that supports a core
 core, constructed from stacked laminations providing the space for the
stator winding
Stator of IM

4. CONSTRUCTION
 Revolving Rotor
 composed of punched laminations, stacked to create a series of rotor
slots, providing space for the rotor winding
 Two basic design types depending on the rotor design
 squirrel-cage
 wound-rotor
Squirrel cage rotor

5. CONSTRUCTION
Wound rotor
slip rings

6. MOTOR OPERATION

7. EQUIVALENT CIRCUIT

8. POWER FLOW IN INDUCTION MOTOR

9. TORQUE-SPEED CHARACTERISTICS
Typical torque-speed characteristics of induction motor

10. MAXIMUM TORQUE
 The corresponding maximum torque of an induction
motor equals
 The slip at maximum torque is directly proportional to the
rotor resistance R2
 The maximum torque is independent of R2
2
max 2 2
2
1
2 ( )
eq
s eq eq eq
V
T
R R X X
 
 
    

11. MAXIMUM TORQUE
Effect of rotor resistance on torque-speed characteristic