VFD motor frame size

[Arulkumar P]

We have the requirement of Sq.induction motor with S1 duty, F class insulation with temperature limted to B class, T3 and the same 50 % of motor start with DOL and 50% start with VFD.
Compare to DOL motor frame size, VFD motor frame size is one size higher than DOL motor frame size of same power rating.
why VFD start motor frame size is higher ???

Is there more insulation than DOL motor???

de-rating is considered for VFD motor???

 

[ozmosis]

What is a Sq.induction motor? Is it squirrel or Square frame?
There is generally no reason to increase the frame size for a VFD rated motor. Maybe it is a very low quality motor.
Perhaps you could be a little more specific on the type and frame size.
Why are you using multiple question marks? we tend to get the point that it is a question when you just use one.

 

[ScusaMe]

When heat is an issue, it is common practice to either force ventilate the motor ....

or


to over-frame-size it.

 

[electricpete]

I have never specified a motor for vfd, but here's my thoughts:

NEMA MG-1 Section 13.2 gives frame assignments based on horsepower and speed.

If you wanted a larger motor to accomodate some derating factors, you'd have to specify a larger horsepower. I don't think it would be standard (IAW MG-1) to specify same horsepower in larger frame size.

Just my thoughts... open to correction. Outside NEMA world is beyond my experience.


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(2B)+(2B)' ?

 

[electricpete]

Correction

NEMA MG-1 Section 13.2 gives frame assignments based on horsepower and speed.
should've been:
NEMA MG-1 Section 13.2 gives frame assignments based on horsepower and speed and enclosure type (ODP, TEFC,etc).





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(2B)+(2B)' ?

 

[ScusaMe]

working on a reply for you, Pete.

I've contacted NEMA for a better explication of 13.2

 

[ScusaMe]

Correction to previous:

I've contacted NEMA for a better explication of Section II, Part 13.