The worst of VFD's

[gcaudill]

Does anyone have any real life experience with VFD's that are bad in terms of dv/dt switching, and that are paticularly hard on motors. I ask because I am looking for a drive to test inverter duty magnet wire for inverter rated motors. The drive should be 575V and available in the USA. In the past we have used AC Tech. Any advise based on hands on experience would be great.

 

[afterhrs]

Maybe a stroll down memory lane may be of some help, I dont know of any indidviduals that use a VFD for that sole purpose.

thread 237-74246

Best regards,
Afterhrs

 

[DickDV]

In essence, what you really are looking for is a drive with a very high carrier frequency and no output signal conditioning. If a drive uses IGBT's, the switching speed for each pulse is going to be nearly the same since each manufacturer is looking for the fastest switch speed to minimize heat in the IGBT.

Mitsubishi has drives out there with an incredible 18-20KHz carrier. That's about as bad as it gets, in my opinion. Now just add 400 ft long motor lead lengths and you've got a real motor insulation tester, especially at 575VAC.

There are days when I would like to do this on purpose just once!!! Sounds like real fun!!!

 

[Marke]

Hello gcaudill

In addition to the comments above, the output switching patter used by different inverters is all different. In some inverters, the switching of positive and negative poles is synchronised and so the shaft currents are minimised without filtering. This will also have an impact on the insulation stress within the motor. Other drives use a totally non synchronised approach and this adds stress.

I would suggest that drives that exhibit poor shaft current performance would suit your needs well.

Mark Empson

http://www.lmphotonics.com