AB 1336-IMPACT "GROUND FAULT"

[mkovac]

Hi All,

I have an AB 1336-IMPACT drive, 460v 3ph 10HP. It will run fine for various periods of time but then trips-out with a "ground fault" #12018. The vfd and the motor and wiring have all been checked numerous times and no ground has been found. Incoming power is fine and I have 5 other identical vfd's running the same type of machinery with no problems. Any ideas? Thanks.

Matt

[mike_Kilroy]

does your motor power cable move (like in a wiretrack)? If so, check again for a metal chip or frayed area that only shorts at a certain location of the track.... not uncommon....

another thing we have found is a loose screw on a terminal strip in series somewhere between the motor and drive, in case u may have any connections between the two....

lastly it is not uncommon if motor has a connector on it, to have it fill with cutting fluid, or have a short that comes and goes....

the bad news is that the vintage of that drive is such that if you don't find it soon you probably will be buying a replacement drive as the ground fault protection works like 60% of the time (60 times out of a hundred - that 61rst blows the output IGBTS), the good news is a lot of folks say you can buy this drive on ebay for $ 50 most anytime (in other forum threads on here).....

[mkovac]

Thanks for the reply. Unfortunately, our application of this drive is in a very dry environment, none of the cabling moves and this thing will trip out without the motor even connected. We use this drive to build coils for large power transformers. The really bad part is I just received the drive back from Rockwell Automation for repair at almost $2,000. I'll start watching ebay. Thanks again.

Matt

[Al_The_Man]

The vfd and the motor and wiring have all been checked numerous times and no ground has been found.
Matt

Has the motor been checked with an insulation Megger to ground?
This instrument places a high voltage on the stator in order to detect ground leakage that may not show up with a low voltage VOM.
Al.

[mkovac]

Our megger has been on loan but is due back this afternoon/tomorrow morning. Will definitely run this test upon arrival. Thanks.

Matt

[mike_Kilroy]

..... this thing will trip out without the motor even connected....
Matt

Matt, if it trips w/o the motor even hooked up, why megger the motor?

[Al_The_Man]

I missed that bit?
Al.

[mkovac]

Good point, but could a problem with the motor or wiring have caused another failure in the drive?.... Probably, but the the failure would not be intermittent, right? We will megger the motor this morning for piece of mind if nothing else. Thanks again.

Matt

[Al_The_Man]

There is also a possibility that one of the IGBT's in the drive output could have a weak insulation problem that flashes over due to the high harmonic spikes that are inherent in these type of drives.
Al.

[Foogl]

If you have identical drives, I would swap it with other one to see, what will happen. Same VFD will fail => bad VFD, VFD on same machine will fail => cables or motor.

[mkovac]

I did have an identical drive and we installed it in the machine once we were sure that the machine itself was ok. With this second drive installed we had no motor movement at all. Both of these drives are currently at Rockwell being re-evaluated. I hope to have an answer soon and will post the result to help anyone else who may run into this situation. a very long and frustrating process. Thanks for the input.

Matt

[mkovac]

Hi all,
The local Allen-Bradley Rep stopped by and personally verified the problems we are having. He gave us a completely different drive to replace the one with the ground fault problem. This machine is now up and running. The other drive was determined to have a weak onboard 10 vdc supply. This drive is being sent back to Rockwell for repair again. Thanks.

Matt