# transformer feeding DC drives.



## mofos be cray (Nov 14, 2016)

Your writing is unclear. But I would suggest that,in principle, you should defer to a qualified tradesman with whom you have a contract.


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## John Valdes (May 17, 2007)

Never ever heard anything like this. And never heard of anyone wanting to bring a GEC to a transformer?


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## varmit (Apr 19, 2009)

What type of electric system is going from the transformer to the machine? Many (most) DC drives or VFDs will not tolerate a delta system either corner grounded or ungrounded. Generally. a wye type system with a center point ground is preferred on any electronic drive, either DC or VFD. 

Could this be a situation where the transformer is "stepping up" the voltage? If so, and a standard transformer is being used back fed, It can only be a delta output from the transformer.


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## MHElectric (Oct 14, 2011)

varmit said:


> What type of electric system is going from the transformer to the machine? Many (most) DC drives or VFDs will not tolerate a delta system either corner grounded or ungrounded. Generally. a wye type system with a center point ground is preferred on any electronic drive, either DC or VFD.
> 
> Could this be a situation where the transformer is "stepping up" the voltage? If so, and a standard transformer is being used back fed, It can only be a delta output from the transformer.


Wow...

This goes quite a bit deeper than my little brain can comprehend. But are you guys saying that bonding a transformer with a GEC (building steel/whatever) with a DC system will screw it up?? What?!!?! Why??


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## paulengr (Oct 8, 2017)

varmit said:


> What type of electric system is going from the transformer to the machine? Many (most) DC drives or VFDs will not tolerate a delta system either corner grounded or ungrounded. Generally. a wye type system with a center point ground is preferred on any electronic drive, either DC or VFD.
> 
> Could this be a situation where the transformer is "stepping up" the voltage? If so, and a standard transformer is being used back fed, It can only be a delta output from the transformer.


Not true at all. It’s just that the surge protection is different on wye vs delta and often there is an LC filter that has to be different, too. If your drive is unable to do it, time to upgrade! I can set you up. The only manufacturer I can think of that almost insists that ONLY grounded 4 wire wye feeds are acceptable and this is from a few years ago is ABB. I know for a fact that all TMEIC drives (Toshiba, GE, Schneider, Mitsubishi, many others), Benshaw, Franklin, LSIS, AB, Yaskawa, Sigma, Danfoss, and Westinghouse drives can do this. However some have a jumper or a switch that you MUST use to work on delta. Others are just configured for delta all the time.


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## paulengr (Oct 8, 2017)

MHElectric said:


> Wow...
> 
> This goes quite a bit deeper than my little brain can comprehend. But are you guys saying that bonding a transformer with a GEC (building steel/whatever) with a DC system will screw it up?? What?!!?! Why??


It’s not the PE input but the DC bus within the drive that is the issue.

Some drive designs split the capacitor bank in half and the midpoint voltage on the DC bus is connected to the neutral. In delta half of the rectifier isn’t firing so the other half is overloaded. Also if there are any LC filters they aren’t going to work correctly either. The solution is to not do this. Use a DC bus reactor for instance or delta connected filters. There are no good reasons to use wye connected components especially when a DC reactor also doubles as an output load reactor.

Also another common thing to do is use say 300 V surge arresters to ground on a 480 V drive instead of 550 V surge arresters phase to phase. It gives “better” protection but it’s a very minor improvement. A typical clamped voltage from a 300 V MOV might be 900-1000 V. On the 550 it might be 1200-1300 V on the exact same surge. Most low voltage IGBTs are rated 1500 V.

If you have a wye only drive on an ungrounded system it won’t last long but you may not realize why they are failing. On corner grounded delta it fails fast (minutes).


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## varmit (Apr 19, 2009)

I was referring to as out "of the box" settings, but I have run into many drives that were not adaptable to a delta system.


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## micromind (Aug 11, 2007)

varmit said:


> I was referring to as out "of the box" settings, but I have run into many drives that were not adaptable to a delta system.


 I've seen at least 2 of them blow up because they were connected to a 240 high-leg ∆ system without taking the appropriate measures. Both 15 HP, on the same job. I was called in to see what happened and to make the new drives not explode.


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