USA 34,5kV zig-zag grounding transformer Specification

[igg1966]

Hello.

Please, can anybody indicate wich are the specification(s) for a 34,5kV zig-zag grounding transformer for a Windfarm in Kansas ( KCP& L Electrical company )?

I guess that this equipment has to comply with IEEE 32 Std. , however I need to know the KCP&L requirements and/or approved manufacturers for this company of Kansas. Thank you in advance for your cooperation.

 

[rbulsara]

That is the type of work, you need to hire professionals and pay for it.

Rafiq Bulsara

http://www.srengineersct.com

 

[igg1966]

I am asking for criteria design and applicable standards that the Electrical Company can give as criteria design and withouth cost.

The electrical Companies usually have a list of approved vendor for each equipment and this is also free of charge.

I am not requiring conceptual design (neither detailed engineering)but only applicable standard for a defined equipment and as a favor.

Knowing the requirements I am able to develop the engineering.

In any case, thanks for your answer.

Best Regards.

 

[waross]

Have you tried asking KCP&L?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[igg1966]

No . I haven't tried it !. I have a companion that will contact them, but due to my responsability in my Company I have to find answers on my own way.

And I have to report to the Management separately from others.

I don't know if you mean on the side that I am...

Thanks for your suggestion.

Bye

 

[tem1234]

Look in IEEE C57 serie for transformer requirement.

Also Ansi C62.92.4 - Guide for the application of neutral grounding in distribution utility system

But there's a lot to look at, like bushing, current transformer... The best is asking to the utility or someone with experience.

 

[dpc]

I doubt that Kansas City Power & Light is going to have a specific standard for grounding transformers. They will probably want it built to applicable ANSI standards. The grounding transformer specs are based on the desired magnitude of ground fault current and the time duration, IIRC.

But isn't this installed on the wind farm's 34.5 kV system, and not the utility's system?



David Castor

http://www.cvoes.com

 

[alehman]

I agree with the above posts. I live and work in KCP&L's service area and my company handles wind projects. As far as I know, they have no such standards. If all else fails I can probably get you in touch with the appropriate engineers. Let me know.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[igg1966]

Good morning.

Thankyou very much tem1234, dpc and specialy for alehman for your help.

Maybe what I am looking for are the design criteria.

I know that the zig-zag grounding transformer is for the limitation of earth fault.

If in the 34.5kV collecting system the fault criteria is a current of 600 A and defining a time (i.e. 10 seconds) that the equipment has to support this current (in spite of protections trip will be shorter than it) and according to applicable ANSI/IEEE Standards (for grounding transformer manufacturing as well as for construction/ installations) my doubt can be solved.

I work in Europe (under IEC Standards that don't usually match with ANSI, NEC, UL or others american codes)and what I am trying is to get an earth fault typical value as well as the design time ( 10 or 15 seconds - i.e.- ) for heat disipation value for the grounding transformer.

Thanks again for your cooperation and good attitude.

Best regards and have a good day.

 

[dpc]

I know that the zig-zag grounding transformer is for the limitation of earth fault

Actually, the grounding transformer is used to provide a source for the ground fault current, not to limit it. And it does not have to be a zig-zag winding. A conventional wye-delta will work also.

David Castor

http://www.cvoes.com

 

[igg1966]

Hi David.

Here in Europe we usually put a reactance (zig-zag configuration) for creating an artificial neutral point in a MV system where the connection of the winding transformer of this side is in delta. So with the help of the reactance we get a route to earth in the case that an earth fault occurs in this MV system.

The reactance is calculated for having an determined impedance which limit the fault current to an designed value ( i.e. 50 A , 300 A, 500 A ) and the heat disipation must be designed for a time around 10 seconds. Also another design value is the permanent current that the reactance can afford to ground: the 3 phases are not exactly the same and some unbalanced small current can go through the ground.

Of course a wye-delta transformer can be used for this goal. And I guess that the wye side are connected to ground...

For this reason I am in this forum, trying to understand the criteria that are usually taken for this matter in USA.

I don't want that anybody work free for me and I appreciate the help of people very friendly like you that doesn't expect anything from the others.

Thanks a lot for your support and your time.

Best Regards.

 

[tem1234]

Here in Canada it work exactly like you describe. We put Zig Zag transformer (or Ygd but it's rare here for this application)

The only thing i would say is that these system are generally solidly grounded here, so the ground fault current are more in the range of 4 - 6 kA, but i don't say it won't work with low reactance grounding.

 

[rcw retired EE]

Part of the criteria is how much ground fault current the utility will let the wind farm add to their system. There may be near-by substations where the equipment or the ground gird design is close to the maximum allowable. In that case, the wind farm would have to limit its contribution.

At the other end of the scale is the need for enough ground fault current to properly operate and coordinate the protective relaying.

In my experience, the utilites have requested a solidly grounded wye winding on the delta-wye step up transformer. We have not installed many grounding transformers,(two out of 50-60) but that could be due to the systems that the plants connected to.

 

[alehman]

What rcwilson said. Zig-zag transformers are fairly unusual in this part of the world (I've never had one on a project). Delta-wye would be the more common approach.

You said 34.5 is the collection voltage. Do you connect to KCP&L's 34.5 kV distribution or is there a dedicated substation? If so, that's what will matters most to them.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.