VFD discussion related to non-inverter rated motors
VFD discussion related to non-inverter rated motors
(OP)
Hello folks,
Is there any thread here that discusses non-inverter rated motors being damaged by VFD's or any technical link that would help me understand how this is so?
Thanks
Is there any thread here that discusses non-inverter rated motors being damaged by VFD's or any technical link that would help me understand how this is so?
Thanks
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata





RE: VFD discussion related to non-inverter rated motors
Better would be a specific question. Can you be more specific? What size, voltage, application?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD discussion related to non-inverter rated motors
http
which has a lot of white papers on the subject of VFDs. Select "Installation Considerations for IGBT AC Drives" which is on page 2. There is considerable information on the reflected wave phenomena in this paper.
About six years ago I designed the power distribution for a winery bottling line. The bottling line equipment supplier supplied both the VFDs (which were A-B) and the motors (which were Reliance at the time a Rockwell company). For some reason the supplier furnished the cheapest basic Reliance motor which has insulation rated at 1000V. Within two weeks the motors started failing, starting with the furthest motor from the control panel. Within three more weeks all 28 VFD motors failed, the closest motor failed last.
I don't think that anyone supplies motors without 1600V pk to pk insulation nowdays. There still is a maximum motor lead length which I usually get from manufacturer's tables which bypasses any calculations.
This is no endorsement of A-B drives, but I am most familiar with them over the other major brands.
RE: VFD discussion related to non-inverter rated motors
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata
RE: VFD discussion related to non-inverter rated motors
Why don't you just use an electronic soft-start which is cheaper and does not have the dv/dt issues that a PWM drive has?
RE: VFD discussion related to non-inverter rated motors
At 460V, as a general rule Insulation Class B is not good enough. You need Class F Insulation.
At 575V, Class F is good enough only for the shortest of motor leads.
If you want to be safe, specify motors with a MG1 Part 31 endorsement. With that, at 460V, at 100hp, you can go out to 250 feet without additional apparatus. That number drops to 60 feet at 10hp. You can extrapolate linearly between those two points.
RE: VFD discussion related to non-inverter rated motors
I have attached a few pages from the A-B Powerflex 700 manual on motor lead length. I have followed the manufacturers length recommendations and never run into a problem. Interesting these tables have varied with the different VFD models of the same manufacturer and between manufacturers. I have always assumed that it had something to do with any output inductance, carrier frequency, IGBT type, and other factors that I don't know about. I always use the 1600V rated motors (NEMA MG1 Part 31) as DickDV mentioned. In these pages you can see the difference in allowable lead length with the different voltage ratings of the insulation (and with carrier frequency).
RE: VFD discussion related to non-inverter rated motors
But regardless of that there are many situations where it is possible to run a standard motor from an inverter without risk. The manual of the inverter should provide information on that.
If that is not feasible applying approbiate filters will provide a solution.
RE: VFD discussion related to non-inverter rated motors
http://www.gambica.org.uk/pdfs/Report2_2nd_ed.pdf
is very complete and contains "all you need to know" about VFD:s and motors.
There is just one little mistake in it; the common mode filters are NOT ferrite rings - they are iron powder toroid cores or wound tape amorph metal cores. Ferrites do not harm, but they do not help much either.
Also, the insulation system letter does not say that a motor can take the steep voltage edges . But most or all insulation systems with special "VFD hardened" insulation also have the higher letters (F and H).
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD discussion related to non-inverter rated motors
That is a great report and is very useful.
Also to expound a little on what electricuwe stated regarding output filters, the tables that I posted with maximum lead length show how some A-B VFD output filters and terminators affect maximum lead length so nightfox1925 can get an idea if they are feasible for his case. I always forget about these output solutions because I don't like to use them but they are useful if you don't have any other means to fix the situation.
RE: VFD discussion related to non-inverter rated motors
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata