Transformers with Multiple Grounding

Maybe your understanding is wrong.

Single point earthing means both transformer use the same earth.

This way you avoid build up of a potential in your earth system.

Are you really doing this work for money or are you just in for education?

Let me clarify some few points;
a) One transformer is grounded through NER, other is left open
b) Both transformer located at different substation.

You wrote, "Both transformer located at different substation."

They are physically distant from each other, do you mean, but otherwise in parallel as you described? (Bear with me, please. Just trying to get the full picture. Thanks).

Yes it is, both of transformers are to be operated in parallel, both are connected in the same bus.both substations belong to the customer in the same plant, I can say less than 100m.

Welcome to CR4, jackdaniel.

Have you discussed these points with your client? Is this practical/productive, or do you plan to after gathering more info? Possibly your client has a reason for wanting the configuration as specified?

I would ask them first and then come back here if you have further questions. We'll do our best to answer them.

For me, no issue, because transformer will operate parallel, either one of them must be grounded.

Follow your local codes. Somebody else will one day work on these transformers. They will expect them to be wired to your local codes. The codes are not written from a theoretical every thing is working as planned basis. The are written from a failure analysis to prevent failure or to fail safely.

Follow your local codes.

There is no local code, I just want to know the reason, my guess, is it the same concept as generator grounding?

No local code? How about, 'Any' code? A national code? Surely there is some kind of code in effect for the substation in question? Surely.

Sorry, there is no "guess" when you have,"Two transformers to be paralleled, 132/33kv and 11/33kv" and don't have a clue what you are doing.

When you guess, you get:

After looking back at all of your previous posts, I wonder how your other projects have gone.

You speak of a client, therefore you are doing this for money. You believe that it's ok to have an ungrounded 132kV transformer since "...grounding is not necessary except for the safety reason...", like safety is an afterthought. You believe that because they are physically located near each other, that they are also electrically near each other, and that the low-side voltages will match perfectly in magnitude and phase. You naively believe that paralleling is just a matter of connecting the low-sides together, without any mention of vector groups or phase shifts through the networks. You think that generators and transformers follow the same grounding philosophy; and that we're going to help you justify your "decision", and for free. You should tell your client that a bunch of anonymous strangers on the web said it was ok to do this during the inquiry that is sure to follow. You are an accident looking for a place to happen. Not on my watch...

Jackdaniel, it is possible we're losing something in the translation? I rather suspect that English is not your native tongue and so what you think you are saying is not we think you are saying? I must admit, I'm confused by your posts.

On the one hand you mention a 'client' who wants things done a certain way and, on the other hand, your interest seems to be purely casual; motivated by curiosity only and having nothing to do with clients and codes.

Are you simply curious about why your client requested this particular configuration? If so, then why not ask your client directly about their rationale for doing this?

Again, this may all be getting lost in the translation.

Here are some other offerings for JD. From these we may be able to discern some pattern in the translation. I am suspect.
NER for GTG
Differential Protection For Transformer And Generator
Transformer Body Earth & Neutral Ground Earth
Single Pole & Double Pole Voltage Transformer
Earthing Mesh Substation
NER Body Termination And Cable Sizing

The more I read the more I think he is an alien living in a substation.

Where on Earth would you, if you do not have a code, not follow one from another country, instead of inventing the wheel all over again?

Let me briefly recap what some of the plan was
There are 2 transformers to be paralleled, 132/33 & 11/33, both transformers are located at different substation & Y connection at secondary , the new transformer to be installed (11/33) at the same bus with 132/33, my client requested ungrounded system for the new transformer grounding, the reason is 132/33 is solidly ground to earth, single ground is enough for paralleling multiple transformers according to my client, but he couldn't give the technical reason, I have been searching in the google but I couldn't find the answer until now, hopefully somebody can give the technical answer.
I'm very clear about what is needed for 2 transformers or more to be paralleled, please do not mention about vector group, impedance, capacity, local code & etc.I want to know the reason why one of the transformer ground to be left opened.

You are a danger to society and everyone who comes in contact with your "work".

<unsubscribe>

Sorry, I don't agree with you, There are many information in the internet nowadays including IEEE & IEC technical papers, most people learn from books, technical papers & reliable information from internet. By using google, you can download many papers not limited to IEEE&IEC.

<...download many papers not limited to IEEE&IEC...>

That's a good idea. It would be better to do that than involve CR4 readers, really.

"my client requested ungrounded system for the new transformer grounding, the reason is 132/33 is solidly ground to earth, single ground is enough for paralleling multiple transformers according to my client, but he couldn't give the technical reason,"

1) Client requested ungrounded system for new transformer.

2) Client claimed single ground is enough for paralleling transformers.

3) Client could not give technical reason for point 2.

Logically:

4) Given the information in point 3, point 2 is unfounded.

5) If point 2 is unfounded, point 1 has no valid information supporting it.

Therefore:

The new transformer should be grounded for safety reasons, if the client does not want that, have the client provide the building code or other documentation to prove that the transformer should be ungrounded.

If you want to know why the client wants one transformer to be ungrounded, I can only speculate that the client is trying to save money by scrimping on safety. This is serious voltage you're dealing with, therefore assume lives are at stake. If the client refuses to allow the new transformer to be grounded, tell him you can not work on such an unsafe design and that you quit. Losing this job is less of a burden than dealing with the inquisitions and hearings after someone dies due to your unsafe practices. And to clarify 'I was only following orders' is not a defense, YOU are the Engineer, YOU are the one to tell the client when he is asking for something unsafe, you are not to build an unsafe design because 'the boss said to do it this way.'

That's like saying please do not mention about the oxygen and nitrogen and their requirement for human life...

...and saying...

...I just want to breathe

Jack, could you clear a couple of points:

What type are the transformers ∆Y, YY or Y autotransformer
The rating of the transformers
Is the 132KV on a common bus

Sorry for lack of information in my last question
Both transformers are fully capable to be paralleled,
a) Dyn11(132/33) & YNd11(33/11)b) 20MVA for both transformersc) I'm not sure, will check again
I want to know why not, both of transformer grounded to the earth, why only one?

Jack, you say the two transformers are a different locations and yet paralleled I assume on both the 33 and 11KV. How are they inter-connected? Baring in mind 20MVA @11KV = 1050A.
Maximum fault current would be getting me worried. Not so much Ph→E, this is limited by the NER's, Ph→Ph is going to be horrendous.

If the object of the exercise is to limit the overall Ph→E current would it be possible to use two NER's per transformer each with a let through of say 250A.
Normal parallel running one NER connected on each transformer, the overall Ph→E limited to 500A. Open bus two NER's per transformer. This would keep the Ph→E current consistent at 500A.
(Not sure this is even acceptable, it's not something that you get asked about everyday.)

I've worked on substations with multiple 20MVA 33/11KV transformers but they were normally open bus. Paralleling lasting a matter of seconds. To be honest we avoided it if we could, if forced in to it we were very twitchy about it.
To be honest I don't know why, how long does it take to close one switch and open another. The chances of a fault during the couple seconds paralleled were pretty remote.

Hi Tony,
Good Advice, From my experience, I haven't seen single ground system and the rest left floating for the parallel operation of transformers, my guess, the client trying to adapt the same concept with parallel generators grounding system, I'm not that level to explain what are differences between both systems ( Generator & Transformer grounding system) , why we can't adapt parallel generators grounding system?
Have you ever encountered this situation before?, have u ever seen multiple transformers operating in parallel with only one transformer grounded and the rest left open?

Sorry, me again. Just had another look at your post.

Have I read this right? The 33/11KV transformers are Y∆? If it is right you've opened a whole new can of worms.
The 11KV can't be earthed via NER's. A high impedance zig-zig earthing auxiliary transformer is needed at both locations.

You sure this isn't homework? It's giving me a headache.

11 at delta side, 33 at Y side, YNd11.
NER through Y is sufficient.

GA

ding ding ding...we have a winner!

I think I have found a good answer.

(A). In two numbers of delta-star, step-down 11/.433KV transformers, the two L.V panels are having a bus-coupler in between, but in your case where one step-down transformer 132/33KV, and one step-up transformer 11/33KV? (B). Each transformer is having a node or point or two which needs to be connected to ground. Like some one explained the single point earthing might mean the same earthing system where both have to be connected to. [P.S. I guess 100% correction, when O.P thanking one really counts...]

I'm aware of that ,but both transformers not connected to the same grounding bus.Each transformer located at different substation.

jackdaniel writes:

>I'm aware of that ,but both transformers not connected to the same grounding >bus.Each transformer located at different substation.

I don't want to argue:

1) A substation may include: 1) transformer (2) H.V panel (3) L.V panel (4) Cap. Bank? (5) Etc.

So, your each transformer is located at different substation? That means each substation comprising of a transformer room, H.V room, L.v room etc.

2) From the above, if you are having two different substations, in turn means two separate L.V or H.V panel's rooms?

3) distribution transformers or transmission transformers? And is it 132/33 K.v and 11/33 K.V as in the first posting? Where is the bus-coupler? If both panels are apart, how would you coupled them? If both panels from both transformers are in the same room, they can be coupled?

4) Both transformers need to be grounded (known as BODY GROUND)

5) Etc.

P.S where is my score? :) I have upload such a nice picture and expla...

Abasin,

Thanks for your questions,

1) Yes.

2) Yes, the distance between two substations approximately 100m, but the ground grids are interconnected.

3) Vector group YNd11, 33 Star, 11 delta, Outgoing cables from 11/33KV trans will be connected to bus at 132/33 substation.

My question was why my client requested single point earthing of transformer.

"My question was why my client requested single point earthing of transformer."

Ah, now we've had a change in terminology. 'single point' earthing is not the same as 'earthing a single transformer and leaving the other unearthed.'

'Single point earthing' beans to being all the earthing lines together to a single point, so when you look at the layout, the earthing forms a 'tree' topology, every earthing line can be traced to a single grounding point, and each line has one and only one path to follow to that point. This is done to avoid 'ground loops,' which are two (or more) earthed points in the system with multiple earthing paths.

When you have a ground loop, there exists the possibility for the loop to be carrying significant current without sending that current to the earthing point or tripping the 'ground fault' breaker. Ground loops are annoying in the recording industry, where a ground loop will put a 50/60Hz 'hum' into any recordings done on the equipment with the ground loop, but at the higher power levels (such as a substation) ground loops can be deadly.

Now, from what I remember from this thread, the situation is such:

1. There are two substations, approximately 100m apart.
2. One transformer is being installed at each substation.
3. The employer wants one transformer grounded, the other ungrounded.

Now I need do do some follow-up questions to solidify the picture.

Are the two substations bounded within the same enclosure? That is, are they on the same property with no features, such as a road or a fence running between them?

Is the equipment at each substation set up in Single Point Earthing, or is each piece earthed individually?

If the substations are using Single Point Earthing, and there is no feature separating the two, are they both earthing to the same point, or are the two substations each earthing to their own Single Point?

One final question, and one I'm afraid to ask, are the substations earthed in a consistent manner, or is the earthing somewhat haphazard, with some components earthed and some not?

I understand what it means by "single point earthing" in electrical term, do not misinterpret in this case, I apologize again for misunderstanding, in this context, single point is defined by earthing a single transformer and leaving the other unearthed or floating.

Okay, in that case, my original advice stands, ground both transformers, or walk away from the project and let some other fool take the fall for 'following the bosses orders' and setting up a dangerous situation that WILL kill someone down the road.

RAMConsult writes:
[This may be a case of misinterpretation. As written you said 132/33 and 11/33, then you changed it to 132/33 and 33/11, to an experienced power engineer there's a big difference. Exactly how are these transformers connected to each other and to the load?]
Exactly my point here...

Sorry, could be type error, I was rushing and I didn't type properly.
These transformers will be connected through the bus coupler 33KV. We have downstream transformers rated at 33/0.433 kv.

A picture is worth 1,000 words as the cliche says.

Perhaps including a schematic of your configuration might clarify things a bit.

You think?

i will post the single line diagram, I understand, without SLD, it's very hard to catch the picture!

But my point was about single point earthing in 2 parallel transformers