VFD drive incoming phase shorted to ground

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adam067

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Hey there, I was powering up a drive today and when i did so one of the wires on the incoming terminals has a strand sticking out of it which in turn caused Phase C to short to ground. I took out phase C fuse in the panel as well as tripped the breaker. My question is is this drive still good? or how can i test to make sure it is. I did not smell any burning diodes. It is a powerflex 700 drive (100hp). Thanks
 
adam067 said:
Hey there, I was powering up a drive today and when i did so one of the wires on the incoming terminals has a strand sticking out of it which in turn caused Phase C to short to ground. I took out phase C fuse in the panel as well as tripped the breaker. My question is is this drive still good? or how can i test to make sure it is. I did not smell any burning diodes. It is a powerflex 700 drive (100hp). Thanks
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What does a burning diode smell like?

As long as you did not short it out on the output side of the VFD it won't matter at all.

Power it up and see what happens. The drive will either work or it won't.
 
petersonra said:
What does a burning diode smell like?

As long as you did not short it out on the output side of the VFD it won't matter at all.

Power it up and see what happens. The drive will either work or it won't.
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Yep, I'd have to agree. If you did short the diodes connected to that phase, they would be conducting in both directions and the DC bus ripple would be off the charts, so the VFD would immediately shut down the output (inverter) section and display a fault #17. You might have that fault from the initial action and it should be able to reset, if not, the rectifier section is hurt.

If there is a steady red LED on the front and a fault code that is #900 and up, that is a fatal fault and your drive is toast.
 
petersonra said:
What does a burning diode smell like?

As long as you did not short it out on the output side of the VFD it won't matter at all.

Power it up and see what happens. The drive will either work or it won't.
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I have not not yet powered it back up. I did check the dc side with the diode check function and all readings are between 300 and 600 which is good according to the test you are supposed to preform, I am an electrician it's just when it comes to the guts of a vfd I'm lost. Thanks for the input I really hope it's alright.
 
You blew fuse and popped breaker simply because you shorted one of the 3 ph power supply lines to ground. This has NOTHING to do with the drive.

Put a fuse in series with a phase to ground from your plant it will pop. Same thing. Does not effect anything in the drive.

Know that all 3 phase inputs to your drive FLOAT with respect to ground; ie., they make a dc bus, of which neither plus or minus is referenced to ground.

So your drive is fine.
 
mike_kilroy said:
You blew fuse and popped breaker simply because you shorted one of the 3 ph power supply lines to ground. This has NOTHING to do with the drive.

Put a fuse in series with a phase to ground from your plant it will pop. Same thing. Does not effect anything in the drive.

Know that all 3 phase inputs to your drive FLOAT with respect to ground; ie., they make a dc bus, of which neither plus or minus is referenced to ground.

So your drive is fine.
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Well, on all PowerFlex drives there is a set of MOVs protecting the rectifier section, configured in a Wye to a ground reference. There is a jumper that is supposed to be removed (as per the instruction manual) if the supply is an ungrounded Delta (so that the MOVs don't try to become a Wye point for the the entire system). So depending on what he has and whether or not the installer read the manual (and understood it), there actually MAY be a ground reference to worry about.

literature.rockwellautomation.com/idc/groups/literature/documents/in/20b-in021_-en-p.pdf
 
You did not damage the vfd. What you did is no different than if you put a fuse and breaker in series with a wire from one of your supply phases directly to ground - it will blow the fuse and open the breaker. It has nothing to do with the drive - which is further downstream from your short.

NONE of your 3 phases of power input in your vfd are referenced to ground inside the vfd. They simply get rectified and make a dc bus, which also is not referenced to ground. So there is no path to ground in the vfd to cause harm.

You drive is fine.
 
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Since the fault was on the supply side it is not only same thing as others have mentioned, it is also the same thing as if there were a line to ground fault back at the service equipment or even at the power source. The drive was not a part of the fault current path and should not have suffered anything. The most the drive probably saw was reduced voltage on the line that faulted - but only for a few milliseconds that it took to open the overcurrent device, well if it was a fuse and the other two lines were unaffected I guess it saw reduced voltage until the fuse was restored, which still shouldn't hurt anything, if the drive were running a load it would still run with only two input lines, but the output capacity would be reduced.
 
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