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Transformer vector groups

Transformer vector groups

Transformer vector groups

(OP)
Hi,
We have 4 off 132/11kV YNd1 transformers on site but are replacing two of them due to age. We witnessed the factory tests last week but were told that a request had been made to chenge the vector group of the 2 new transformers to YNd11. Apparently this is because there has been a c**k up on the design and the HV connection to the HV bushings is now to be BYR rather than the conventional RYB (in old money). Can anyone explain how changing the vector group to YNd11  and then changing the HV phasing to BYR convert the output of the transformer back to the require phase rotation?  

RE: Transformer vector groups

Black magic.  A few threads down there is reference to a paper on the Basler web site about transformer vectors and connections.

RE: Transformer vector groups

Interchange R& B  incoming line connections to transformer on both primary and secondary sides.

RE: Transformer vector groups

(OP)
Hi, the 'experts' are proposing to swap the primary side L1 and L3 phases only on the YNd11 transformers. We on site are objecting this as we can't work out how this will allow the YNd1 and YNd11 transformers to be operated in parallel.

RE: Transformer vector groups

Why not, did you read the paper on the Basler site?  There is a bit more to it than just a single swap, but any YNd can be reconnected as any other YNd, all six of them.

RE: Transformer vector groups

As this comes up occasionally I thought I'd write a quick note on how changing the connection on a transformer can change the vector group.

RE: Transformer vector groups

(OP)
Thanks for all the advice. So finally, as the Red and Blue (L1 and L3) phases have been swapped on the primary and secondary sides of the transformer, this will have no effect on phase rotation etc on any existing motors? Wouldn't like to think that all the 3 phase drives fed from the 11kV boards and lower would start to operate in reverse.

RE: Transformer vector groups

sibeen,
I don't understand your diagrams.  The Winding 1 voltage should be in phase with Winding 4.  On a Dyn1 transformer, the secondary line-to-neutral voltage r-n lags the primary line-to-neutral voltage R-n.  Your diagram shows r-n in phase with R-n.
 

RE: Transformer vector groups

sibeen,
I don't understand your diagrams.


jghrist, the only possible reason I can see for you not understanding the diagrams is because they were a complete cock-up, incorrect, wrong, mistaken and erroneous.

*please insert an embarrassed emoticon at this point*

I can only throw myself on the mercy of the court and claim that I was arguing with the wife, yelling at the kids, kicking the dog and drinking way too much beer at the time.

I have inserted a changed drawing.


 

RE: Transformer vector groups

(OP)
Hi all, thanks for all of the replies. The proverbial penny has finally dropped (at last).

Is it common for transformers with varying vector groups to be connected in parallel and the external connections changed to compensate for this? I am not in a utilities industry but even after talking to other more experienced power engineers they have never come across this either. I always thought the basics for transformers in parallel were: same vector group, similar/same impedance, similar/same rating etc etc.

RE: Transformer vector groups

The standard vector arrangement used in the generating utility that I worked for in New Zealand was Ynd3, which is relatively uncommon.  When purchasing second hand transformers, we would often need to swap the phases to get correct vector group.  Why Ynd3, I have no idea... tradition, I guess!

RE: Transformer vector groups

William, what you need to do, and why I never provided more than a reference, is that you need to do the vector analysis yourself and convince yourself that you have it right.

A hint: the transformer itself knows nothing about vector groups.  The nameplate shows what the factory thought as the most probable vector group, but any Dy or Yd transformer can have any of the odd numbered vector groups.   What is important is that you see how it works.  Draw out the diagrams and thoroughly understand it for yourself.  Don't proceed further based on anything from the internet, but know for yourself that it is correct.

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