In this presentation Methods of speed control of 3 phase induction motors are presented. Speed of three phase induction motor can be controlled from 1) Stator Side or from 2) Rotor Side

1. Speed Control of Three Phase
Induction Motor
Induction motors are popular due to the
following advantages
• Simple and rugged in construction
• Cheaper in cost
• Maintenance free
• Can be operated in polluted and explosive
environments
• Self starting

2. Speed Control of Three Phase
Induction Motor
One of the main disadvantages of induction
motors is that speed control of induction motors are
difficult. Hence for fine speed control applications dc
motors are used in place of induction motors. Due to
advance in power electronics, variable frequency
drives using induction motors are used
in industries for speed control now a days.

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4. Speed Control of Three Phase
Induction Motor
As induction motors are widely being used, their
speed control may be required in many applications
Speed Control
Speed control for stator side
Speed control for rotor side

5. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V

6. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V
• Applied voltage can be varied by using a three phase auto transformer
• Auto transformer also helps in safe starting

7. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V
• Applied voltage can be varied by using a Rheostat in each input line
conductor
• Also helps in safe starting of motor
• Very inefficient method

8. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V

9. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V

10. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Voltage
V

11. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Frequency
F

12. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Frequency
F
• Constant V/F Control
Frequency of applied voltage cannot be varied
alone otherwise it will change the flux density in
the core and lead to the wastage of energy.
Voltage is varied inversely to the frequency so
that flux density in the motor core remain
maintained and the magnetic material of the
motor get fully utilized.

13. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Frequency
F

14. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By Changing The Applied Frequency
F

15. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By changing the number of stator poles
F
120*50/4 = 1500 RPM
120*50/6 = 1000 RPM
120*50/2 = 3000 RPM

16. Speed Control of Three Phase
Induction Motor
Speed Control From Stator Side
Speed control for stator side
o By changing the number of stator poles
F

17. Speed Control of Three Phase
Induction Motor
Speed Control From Rotor Side

18. Speed Control of Three Phase
Induction Motor
Speed Control From Rotor Side

19. Speed Control of Three Phase
Induction Motor
Speed Control From Rotor Side
o Rotor resistance control

20. Speed Control of Three Phase
Induction Motor
Speed Control From Rotor Side
o Cascaded control
1) When only motor A works, N = 120f/P1
2) When only motor B works, N = 120f/P2
3) When A and B work in same direction,
N = 120f/(P1 + P2)
4) When A and B work in opposite direction,
N = 120f/(P1 - P2)