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induction motor supersynchronous speed control


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#1 rup_loc

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Posted 17 July 2002 - 04:59 AM

Is it possible to control the speed of a 4-pole 50 Hz induction motor over its synchronous speed. I need to run the motor between 1800 rpm and 2100 rpm.

#2 marke

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Posted 17 July 2002 - 05:34 AM

Hello yup_loc
Welcome to the forum.
Yes, you can certainly overspeed an induction motor using a variable speed drive. There are a few things to note however:
1] If you overspeed an induction motor, you can put more stress on the bearings. If you overspeed by a small amount, then there won't be a problem. If you overspeed by more than 50%, it would pay to check with the motor supplier incase the bearings are compromised.
2] Using a variable speed drive on an induction motor will control the frequency and the voltage. This is essential in order to prevent the motor from overheating at low speeds. When operating below the rated frequency, the motor and drive will produce the rated torque only- i.e. the power rating of the motor reduces with speed. When operating above rated frequency, the output voltage is limited to the supply voltage and so can not be increased with increasing frequency. This results in a reducing flux in the iron and consequently, a reducing torque capacity. This limits the power output to the motor rating above rated speed.
3] The torque of the driven load will often increase with increased speed, so it may be necessary to increase the size of motor to control the driven load at the higher speed.

Hope this helps,
Best regards,
Mark.
;e;

#3 rup_loc

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Posted 18 July 2002 - 04:24 PM

Thanks Marke

#4 Carl

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Posted 30 May 2005 - 07:32 PM

I've run motors in the past at speds above the base speed of the motor. You start loosing torque at frquencies above 50 Hz . If the load is large then regine could become a problem when slowing down. Most cemmercial inveters either have a "brake" resistor pre built or you can fit one externally .. if this poves to be a problem.




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