Grounding practice on Medium Voltage systems

[MBfreak]

Hello to all.
At the tender age of 69 I am still working in the electrical power industry as consulting engineer.
In the 60/70s I worked in a large open cast iron ore mine, where much equipment was fed by 12/4,16 15 MVA YNd transformers. All equipment was GE and Westinghouse and engineered and manufactured in the US. The transformer d ( 4,16 kv) side was grounded thru a resistor that was connected to a midpoint tap on one of the legs in the d-winding.
This has come up a very attractive solution in a recent job. NOBODY has tried it in Europe. Ever . So, it´s a bit uphill to get it thru.
I am trying to find relevant documentation that describes this midpoint-grounded solution.
Can anybody please point me in the right direction. Trawling has not come up with any useful info, to me at least.

All help MUCH appreciated.

Ola

 

[cybrdyke]

You can try the tech line at Hammond Power Solutions. They are in Guelph Canada. They make the biggest transformers in the world. They might have knowledge of this.

 

[Chilliwack Murray]

Wow, that's way outta left field...

Anyway, typically (at least in Canadian mines) a zigzag transformer is used to create a reference point for protection when the system is a true delta or the starpoint cannot be resistance grounded.

Startco/Littlefuse are one of the more common systems... Google startco tn-rg12 for details. This document have probably the best explanation of this type of protection.

Another common relay and protection supplier is igard, these are more commonly used in datacenters rather than mining. You can also find info on the IEEE website or many of the transformer suppliers.

 

[alfredeneuman]

This may be of some help:

http://apps.geindustrial.com/publibrary/checkout/System NGR?TNR=White Papers|System NGR|generic

It compares the various methods of grounding with their pros and cons

 

[_Dock_]

Transformers of this size are out of my wheelhouse. I have worked with these folks on a few projects before and they have done some field inspections on equipment for my company before. They're not cheap but if anybody would know a solution to your problem its them.... If you cant find any advice for free they'd be worth a call.

http://cepower.net/

 

[wyliesdiesels]

Yeah transformers this size are out of my league too but Im always interested in grounding.

The highest voltage i work on is 480v...

 

[rockwithjason]

a search of "high resistance grounding" will turn up many papers on the subject as well as equipment catalogs

 

[foolishpride]

Although, I work with large transformers that are 138 KV Delta Primary, and 13.8 KV Secondary, the Neutral Resistors on these units are connected to the secondary neutral. Not familiar with your setup.

Try asking here:
http://www.eng-tips.com/threadminder.cfm?pid=238&page=1

There are many Power Systems Engineers around the world who frequent this message board.

 

[MBfreak]

The burden of being deep into engineering, ie facts and not opinions is something I gladly carry. Of course " Wow, that's way outta left field.." is true for the larger part of us GJers, but I have on several occasions got very relevant input from this excellent forum.

I managed to find a relevant paper at last. Thanks to a friend who is a technical paper hoarder and finds his way thru all of it!
Symmetrical Components for Power Systems Engineering
J Lewis Blackburn, Consultant, Bothell, Washington
Marcel Dekker Inc.

He treats the subject very well and this excellent paper I will use to see if I can get the subject off the ground with a very large European Utility.

Thanks a lot for all input.

Ola