Speed Control for Induction Motors
Speed Control for Induction Motors
(OP)
Found this in an Electrical Engineering reference document.
All of Section 18 in the attached document seems poorly written. Second paragraph in Section 18 is very confusing to me. To change speed in an induction motor, I thought a VFD was required (PWM, etc) to change in the stator.
Any help with this explanation would be appreciated.
All of Section 18 in the attached document seems poorly written. Second paragraph in Section 18 is very confusing to me. To change speed in an induction motor, I thought a VFD was required (PWM, etc) to change in the stator.
Any help with this explanation would be appreciated.
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RE: Speed Control for Induction Motors
Your reference looks old. Older than me. VFDs are currently the best alternative 99% of the time for variable speed induction motors.
If you have a more specific question, let us know.
RE: Speed Control for Induction Motors
There are other ways of doing speed control than with a VFD. Stator voltage is a control variable that is commonly used for smaller fans, usually in the FHP range. But I have a couple of speed controllable motors with 1.5 and 2.2 kW. The trick is to have a high enough rotor resistance so that slip increases as voltage is taken down. The losses are kept within reasonable limits due to the fact that a fan needs less torque at lower speeds.
The other method, that gets mentioned in the text, is to change rotor resistance or changing the voltage seen by the slip rings. There are different methods and the cascade control method is mentioned. Both needs a WRIM.
The cascade can either use another machine or a solid state device. Usually a rectifier and a thyristor controller.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Speed Control for Induction Motors
Bill
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