Zig-zag 60 degree phase shifting transformer

[stevenal]

The situation: Neighboring utility uses the the same voltage wye grounded system as we do, but is shifted from us by 60 degrees. In order to allow a closed transition transfer, our neighbor is proposing to use a delta/zig-zag phase shifting transformer. I know zig-zags are used for grounding, but fail to see how ground currents would pass to the delta side without getting trapped in the delta connection. Can anyone explain?

 

[cranky108]

No, because you will not pass ground currents. But you need a zero sequence source or your ground relays will not work.

 

[stevenal]

Thanks. The connection will also not have a ground reference on the delta side. Once the normal wye source is removed, voltages will be all over the place due to normal unbalance. Agreed?

 

[waross]

How about a wye/delta transformer with one set of connections reversed?


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[davidbeach]

Can't get 60 degrees out of a wye/delta no matter how hard you try. Need another cup of coffee Bill? ;-)

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

"Need another cup of coffee Bill?" Probably a good idea David.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[cranky108]

You can get a 60 degree shift out of a Y-Y. But only if you shift the leads on one side from neutral to bushing.
That would avoid a zig zag.

 

[stevenal]

Thanks cranky. I think you mean a YNyn6 connection? That's what I determined, it will allow unbalanced load currents when feeding in either direction. This realization led to my next question regarding the need for a tertiary.

 

[cranky108]

We use phantom tertiary's in larger auto transformers, as it make the protection of such easer. But buried tertiaries, is not that bad either. But either one will add a zero sequence source. The question might be if you need another ground source.

 

[stevenal]

Cranky,
I'd love to here more about this, since we have some auto-transformers coming up also. For continuity, let's continue in the other thread thread238-514665. I believe the zz/delta is off the table.