vfd motor

Yes and no! I've been proven wrong with an application with a 5 kV motor as to what I learned in a seminar. However, I believe there is a difference. Winding temperature that VFD motors account for insofar as longevity is concerned. I think that VFD cable should be used to afford for high frequency voltages. It is my opinion that you shoud apply a motor/cable to the application and in the case of VFD's, read the instructions. Some people are full of crap (or out of money), do it right the first time!

The harmonics that VFD's inject can degrade some dielectrics(insulation) and increase heating loss in windings and motor iron. Motors NOT rated for VFD operation may run hotter than normal and the insulation may break down prematurely. There is no way to predict IF or WHEN this will happen.

If a standard motor was over-built and conservatively rated, it could run fine off a VFD. It is also possible that a VFD could damage a lesser built motor in a fairly short time.

Motors RATED for VFD operation have been specifically designed to handle VFD harmonics and should provide the most reliable long term operation.

Good information can be found here:

http://cr4.globalspec.com/thread/40051

- MS

As you know any VFD supplies fast transients (pulses) only to the motor. These fast dv/dt pulses impose a huge voltage stress on the motor winding insulation. So, many normal motors may not be insulated to withstand this kind of stress. An inverter duty motor has a special carona resistant insulation to withstand these pulses.

Besides you have to consider that certain VFD can produce Common mode currents thats flows trough the bearings damaging it. You can solve this using ceramic bearinngs, non conductive grease, special feeding cable etc.

Ya! Pal! That could be another problem! Thanks for the input.

High VFD switching frequencies do increase core losses. Main problem though is the ability to drive motor at lower than rated speed at not derated currents but dramaticaly decreased fan cooling capacity. That's the more common cause of failure in normal motors if this factor is not taken into account