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Effects Of Low Frequencies On 3phase Induction Motor Performance


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#1 ajid

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Posted 13 December 2008 - 09:43 AM

VFD can reduce the frequency. but,
is it any effects of low frequency on induction motor??
is there a minimum limit of frequency to keep motor performance??
is there any equations or formulas to get the minimum limit of frequency??
or if the frequency is too low, what will be happen on induction motor?? is it be off??

if the specification of motor:
744 kW, 6300V, 10 Poles, 600 rpm, 50 Hz

what is the minimum limit of frequency??

please response this topic on this forum or send me an email on akukiajid@yahoo.com

Thanks

#2 mariomaggi

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Posted 13 December 2008 - 09:44 PM

ajid,
[quote name='ajid' date='Dec 13 2008, 10:43 AM' post='9621']

> is it any effects of low frequency on induction motor??

no.

>is there a minimum limit of frequency to keep motor performance??
Performances are mainly due to inverter type and feedback control.

> is there any equations or formulas to get the minimum limit of frequency??
I don't think so. Minimum frequency should be also very low, near zero.


> or if the frequency is too low, what will be happen on induction motor?? is it be off??
Performances near zero speed are depending mainly from inverter vector or V/f control

> if the specification of motor:
> 744 kW, 6300V, 10 Poles, 600 rpm, 50 Hz
> what is the minimum limit of frequency??
Minimum speed is related mainly to the type of load (quadratic torque, constant torque, constant power)

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Mario

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#3 marke

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Posted 14 December 2008 - 05:53 PM

As you reduce the frequency applied to an induction motor, it slows down.
This reduces the cooling and therefore you must be careful not to overheat the motor, plus as the frequency reduces, the available power reduces. The torque remains constant, but speed times torque equals power so the power reduces.
At speeds below 10 Hz, the torque in practice will also drop, so if you need high torque, use a gear box to increase the speed of the motor relative to the shaft speed.

Best regards,
Mark.




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