VFDs and Slip Frequency. A question for the Gurus. 2

[waross]

I am wondering if the slip frequency in either RPM or Hz below synchronous speed has the same effect on motor performance regardless of the actual speed.

Put it another way: Starting with a speed/torque curve of an induction motor, If we label the speed axis as slip speed, either in RPM or Hz, (Not in percentage) and starting with zero at synchronous speed and increasing to 100% or 60 Hz at zero speed, can we then use the curve for any commanded speed?

eg: If full load current and torque occur at 40 RPM slip or 1.33 Hz, will we find full load torque at 40 RPM slip, rgardless of the output frequency of the VFD?

Is the slip frequency the primary cause of torque or are there other factors involved?

I think that this is so, but I would like confirmation.
My school days and my library predate VFDs by a few decades and I would like to be sure of my understanding.
On the other hand ask me something about Amplidynes. grin
Thanks

Bill
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"Why not the best?"
Jimmy Carter

 

[jraef]

Bill,
The winding insulation will be the same for 230V as 460V. The speed may become an issue with regard to balancing (vibration) and the speed rating of the bearings. But if you start with a 4 pole motor and go to 120Hz, you are at the speed of a 2 pole motor, so would the balancing and bearings be any different there either? 25 years ago, maybe, but not so much any more. Mfrs like to keep things simple by using the same inventory of component parts for multiple configurations. What I always tell people is to check with the motor manufacturer you are using (and get an answer in writing). That's where the real issues reside.

Where you get into more possible trouble is if you start off with a 2 pole motor and run it at 120Hz, because now your synch speed is 7200RPM, 2x the standard speed of a 2 pole motor.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden