Motor Temperatures of inverter duty rated vs non inverter duty rated

[KKADM]

Looking for some clarification....
I recently had a discussion involving motor surface temps.
I am under the impression that an inverter duty rated motor (per MG1 part 31) would not necessarily run cooler as far as surface temperature is concerned when compared to a non inverter duty rated motor. I realize there are several factors in motor design that would effect the surface temp. Lets assume we had two identical motors, one rewound for inverter duty and one not.

 

[djs]

I may be wrong, but I am under the impression that inverter duty motors have a higher voltage insulation level. This is due to the PMW wave forms causeing volatge spikes.

 

[thewaterman]

i have inspected lots of motors with a thermal camera, the enviroment is the key factor i'd say, most problems are the air supply in the cooling fan, dirt build up on the cowlings restricting air supply to the windings, tends to get neglected through lack of maint. not sure on your question. but would say the difference wont be great.

 

[itsmoked]

The temperature difference will not be significant. Remember that a system with a VFD is only a few percent less efficient and most of that is lost in the inverter not the motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

KKADM - The motor temperature depends on the quality of the VFD output i.e. how closer to the output is to sinusoidal.

The VFD duty motors fail more due to improper insulation (against high dv/dt) than due to temperature.

Muthu

http://www.edison.co.in

 

[DickDV]

And, if both are Class F motors, both are designed to the same max temp at 40 degrees C ambient and max temp rise due to load. So there shouldn't be much difference thermally.

 

[Skogsgurra]

This was an important consideration before PWM. But not now, anymore.
The early VFDs put out a crude 'square' wave that was very rich in harmonics. That square wave made the motor run with a high percentage of torque ripple, effectively accelerating/decelerating within every cycle. The repeated acc/decel heated the motor a lot more than a sinewave did,
So, that is why inverter motors were less efficient than DOL motors. But not these days.
Inverter duty motors is almost entirely about insulation. There may be some influence from lamination thickness and I think that most motors have thinner laminations today. Not quite sure about that. Muthu?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[edison123]

Gunnar

Today the core laminations have been reduced to just 2 thicknesses - 0.35 & 0.50 mm, with the lower thickness costing a bit more.

Muthu

http://www.edison.co.in

 

[Skogsgurra]

Thanks. That is probably to reduce eddy current losses.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[nate4067]

inverter duty(1000:1ct) motors have class h insulation 180c (356f)@ class b rise

non inverter duty motors (10:1vt 4:1ct) have class f insulation 155c (311f)

There are alot of Variables when selecting vfd motor combination

nathan