# PowerFlex 700S Failures



## baldtrician (Nov 13, 2012)

We have 4- 50hp drive controlled winch motors. The drive cabinets are in an exhaust drift in an underground mine, and are not in a controlled environment. Since install we have lost 6 drives- 2 because of the MOV jumpers, 1 because of contamination (those three were at commissioning), and the other 3 while during operation. Rockwell says there is indication of arcing between the AC and DC busses, but no root cause failure has been completed. All the drives are fed from the same 600V-400A splitter that is 1600 feet from the source. Each drive has a harmonic filter with a line reactor, as well as a load reactor. There is a resistor bank for the regen off the winches.
We have tryed to mitgate the contamination issue by pressurizing the drive cabinets, and we are leaning towards transients causing the failures. There are no over-voltage indications from the drive.
We are grasping at straws, right now. Is there any value in isolation transformers ahead of the filters, do we have a grounding issue?
Any thoughts, experience with mystery drive failures?


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## JRaef (Mar 23, 2009)

It might be a grounding issue, is your system 600V Delta or 600/347 Wye? Is it ungrounded, solidly grounded or resistance/reactance grounded? Did anyone at Rockwell ask you these questions already? Or are you only talking to salesmen?


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## baldtrician (Nov 13, 2012)

It is a 600V wye-system, resistance grounded. Yes we have given all the system specs and single lines to Rockwell, and we have talked to everyone and their dog at Rockwell- except someone who knows what is going on.


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## Jabberwoky (Sep 2, 2012)

Have you tried running without the load reactor? I was always told to never use load reactors with regen drives. There is probably a reason, I just never looked into the why.

I'd be interested in the fault history of the drives if you have that info.


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## baldtrician (Nov 13, 2012)

Jabberwoky said:


> Have you tried running without the load reactor? I was always told to never use load reactors with regen drives. There is probably a reason, I just never looked into the why.


 
The reactors were spec'ed by Rockwell, so no we haven't tryed without them, but I will bring it up in our next meeting.


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## Jabberwoky (Sep 2, 2012)

It may be just line regen drives and load reactors. I did not do many of the new drive installs so the advice may not be reliable. Rockwell has a document on Wiring and Grounding on their website. Try browsing that file and see if anything there gives you an idea. Also, did Rockwell tell you what exactly failed on the drives other than evidence of arcing? I'll check back here later tonight after work.


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## baldtrician (Nov 13, 2012)

They have noted a possible failure of an incoming diode, but nothing concrete so far.


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## JRaef (Mar 23, 2009)

Did anyone think to check to make sure the braking resistors are still good? If the Brake Transistor fires into a braking resistor bank that is not really there on not up to the task, then the DC bus voltage can build up really fast if you are expecting it to be there.


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## baldtrician (Nov 13, 2012)

The resistors were checked after the first failures. I will check with site to see if they are still operational, although we are not getting any over-voltage trips through the drive, thus the frustration in nailing down the issue.


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## varmit (Apr 19, 2009)

What type of mine? If it is coal, coal dust can be conductive. What is the type and condition of the load cables/conductors? Is there separation between load cables? I would assume that the cable is some sort of rubber jacketed multi conductor in a very wet environment. Have you megged the cables? What is the peak line voltage? If this is a 600 volt system, there is not a huge input over voltage tolerance. 

As with most things, there is probably not not one fatal problem, but some combination of minor problems that cause the failures. I assume that you have now removed all of the MOV jumpers? A PF700 has three of these.


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## Mr.C (Dec 20, 2009)

Sounds like a service trip is in order, where is this mine?


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## baldtrician (Nov 13, 2012)

We have had one of our guys go up there, just after Christmas, with a power quality monitor, so hopefully I'll have more details in the next little while. It is not a coal mine, it is gold, but we are sinking a shaft so it has been subject to blast smoke and diesel eshaust. 
Like I said more details to come.


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## Mr.C (Dec 20, 2009)

What kind of mine hoist are you using?


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## Mr.C (Dec 20, 2009)

You mention arcing from the AC to the DC bus? Interesting. Conductive contamination could possibly contribute to this and also high voltage potential. But it does take 10,000 volts to ionize 1 inch of atmosphere so if there is arcing between the busses atmospheric contamination may play a part in your problem as it would decrease the resistance of the medium 'atmosphere' between the busses and therefor reduce the amount of potential needed to arc 'establish a ionization path' across the busses. During regen, quadrant 4 lowering you are generating voltages that may be higher than your bus voltage and if the DB is not connected correctly, uh oh.
Here is a very good link to a web page that covers almost all of the basis, it's a very good quick read http://motionsystemdesign.com/mag/feed_vfd_right/
Let us know what you find, Good luck!


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## Peewee0413 (Oct 18, 2012)

Can't hurt to remove the reactors for a test ...


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## baldtrician (Nov 13, 2012)

Just had a meeting with the tech that we sent to site. It looks like conductive contamination is the main culprit. Very dirty inside the cabinet. We are in the process of adding Vortex coolers to the cabinets to pressurize them and try and keep the dust out. Thanks for all the advice and ideas, I will post any more results if the coolers are successful.


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## Peewee0413 (Oct 18, 2012)

I've done work in a copper mine. Full of fine silica dust and high humidity, and never had one fail from contamination.. I would like to see if that was the culprit.


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