VFD & Accidental corner ground

[ptonsparky]

Customer has an ungrounded delta 240v system set up in their factory. No monitoring, nothing. Changing this just isn't going to happen.

We want to put VFDs on two submersible pump motors and of course the instructions say "though shalt not" install on corner grounded systems. Usually it isn't, but every now and again it is. The reason for the pump replacement. What happens to the drive when these faults occur?

 

[raider1]

With an ungrounded system such as you have described, when one of the phase conductors faults to ground you have now, in essence, created a grounded system. When a second phase faults to ground then the overcurrent device will trip.

Chris

 

[jim dungar]

Many drives have capacitors that are connected Line-Ground. If you install one of these on your balanced ungrounded system, you shouldn't have any problems. However if you system becomes grounded then the capacitor will be seeing L-L instead of L-G voltages, which will probably result in smoke and fried components. I know that the Schneider Electric Altivar drives have a 'switch' for removing the capacitor to ground connection.

 

[wirenut1980]

There could also be MOV's connected line to ground, I believe.

 

[ptonsparky]

I will be using an Altivar, if we get the job. Tech support said 240V grounded delta would be no problem as long as I disabled the filter as Jim described. Problem is at the 575V level.