Low, Medium, High GF levels

[ptonsparky]

Customer with relabeled VFDs on vacuum pumps that trip often enough with an Earth Fault code. The Dairy tech usually works on these until he is stumped. We went up and megged the motor & the VFD load side conductors. No faults. The tech always says its the POCO giving bad voltage. OK.

We figured out the drives are ABB and came across the parameter that allows us to disable the GF while the drive is not in operation. Enabled which is the default may cause false positives. We can also set the level of detection. Low for American, Medium for European or HIgh.

What are these levels? 5ma, 30ma, 120ma? (IDK, I just picked #s.)

 

[Jraef]

Nothing in ABB's literature says what those levels are, but I guarantee you they are not related to the typical values you think of for "GFPE". In VFDs, GF detection (current out of one side of the DC bus, but not back through the other side) is ONLY for the output and is mostly there to protect the transistors from being damaged by a high rate of rise in current when there is low or no impedance, as in a ground fault on the output. So the GF detection/protection must be super fast and is usually done with totally separate systems than what are used for everything else; they don't want to wait for a microprocessor to finish some other task.

The Low, Med and High trip levels that ABB provides are supposedly to allow some moderate filtering of possile causes of nuisance GF trips, for example excessive cable capacitance on the output. If your cable length exceeds the maximum recommended distance, the cables start to act like capacitors and the charging current of those 'capacitors" looks a lot like GF current flow. There are other possible issues like that too, especially if your source power is Delta. It should be left at Low and moved to Med only to experiment enough to see if it holds in, same then for the High setting. Even at the High setting, it's still low and fast enough to try to prevent damage to the IGBTs.

The ability to disable the GF protection is ONLY there for when you are getting GF trips while it is NOT running, so that you can try to troubleshoot the cause. You should NEVER disable it to run the motor, it will void the warranty on the drive. If it is tripping on GF while running, then its either a real GF situation that their megger didn't find (a lot of techs don't know they need to use at least a 1000V megger, not a 500V), or its something like the cable capacitance issue.

 

[ptonsparky]

Disabling the GF would void any warranties. Won’t happen via me.

We don’t know when they are tripping. We just know that Earth Fault were the most prevalent on both drives. Same setup for each that are manually alternated. I think daily but don’t know.

They used 1000 volt.. Distance is less than 10’. Not VFD cable. However I believe it is THHN. Hmmm...XHHW time?

 

[Jraef]

I would set them to Medium and see if that makes the problem go away.

But you said "Dairy tech"? Dairies and VFDs have a long history of touchy cohabitation, especially with respect to grounding issues. Might be worth a very thorough investigation.

 

[ptonsparky]

That part of the dairy has EGs. Four of the seven other building.. Nada. There used to be rods, ,but they are no longer connected.

 

[Cow]

Is there any chance someone put RFI filters on the load side of the drive by accident rather than the line side?

We do work for several different dairies that have or had AB, Telemecanique, Mitsubishi, Yaskawa, AC Tech and ABB drives on their vacuum pumps. I've never had an ongoing ground fault issue with those brands that I recall. Most of them now have TCI KDR line reactors and MTE RFI filters on the line side though, but we never had problems before those were installed either.

I'm not sure if a person at this point should try a 3% line reactor to help buffer the incoming utility voltage if you think it may be making the drive act wacky(they're never a bad thing), or if a person should try a different drive out of a different batch??

Have you tried ABB tech support?

 

[ptonsparky]

Is there any chance someone put RFI filters on the load side of the drive by accident rather than the line side?

We do work for several different dairies that have or had AB, Telemecanique, Mitsubishi, Yaskawa, AC Tech and ABB drives on their vacuum pumps. I've never had an ongoing ground fault issue with those brands that I recall. Most of them now have TCI KDR line reactors and MTE RFI filters on the line side though, but we never had problems before those were installed either.

I'm not sure if a person at this point should try a 3% line reactor to help buffer the incoming utility voltage if you think it may be making the drive act wacky(they're never a bad thing), or if a person should try a different drive out of a different batch??

Have you tried ABB tech support?

The pumps came as a complete system. No reactors line or load that I know of, but I will confirm. There are number of PFC associated with cooling compressors but no record of over-voltage errors. The POCO keeps very close tabs on this customer so troubles on the supply side are noticed and I am told when I ask.

Like I said before, the Dairy tech works with this equipment, via the equipment supplier. When I suggested changing the sensitivity levels, you could tell from there, it was not appreciated. We megged it, not much else I can do until the manager or owner steps in.