Autotransformers 2

[bxny]

Is there a phase shift through a wye-wye, 500kV-230kV autotransformer with a 'buried' delta tertiary? Or is it a zero phase shift, as is the case with two-winding, wyw-wye transformers?
Thanks, in advance, for the help.

 

[davidbeach]

0[°], 120[°], or 240[°] shift; depends on the connections.

 

[bxny]

Thanks, davidbeach. However, forgive me for being a little dense, but, would you mind expanding on what you mean by 'depends on the connections'?
Thanks!

 

[davidbeach]

A-H1, a-X1; B-H2, b-X2; C-H3, c-X3 is 0[°].
A-H1, c-X1; B-H2, a-X2; C-H3, b-X3 is high leads low by 120[°].

 

[bxny]

thanks, again, davidbeach.

 

[prc]

david, Have you ever seen the 120 degree lead connection that you mentioned in your mail being used in any EHV auto transformers? I have never seen it actually used. Where such an auto connection is used?

 

[davidbeach]

It is possible. If it is possible it exists somewhere. No, I've never seen it. But until I drew it up I'd never seen the connection that the standby transformer will have at one of our power plants so that the standby source lags the normal source by 30[°] instead of leading by 30[°] as it does now. Somewhere, sometime, somebody has needed that 120[°] shift and used it, I just don't know where, when, or why.

 

[waross]

David;
Isn't that more a matter of rolling or re-labeling the phases?
It seems to be something like calling one side of a center tapped transformer winding a 180 degree phase shift.
However, I agree with you that it has probably been done.
I seem to remember a circuit where tapped delta windings were used to develop a small phase shift. (Yes the voltage does drop as the phase is shifted).
I suppose that you could interconnect the "B" phase secondary with the "A" phase primary to develop a phase shift.
Now if you used such a transformer in parallel with a non phase shifting transformer on the ends of a pair of transmission lines, you may get a very interesting division of real power and reactive power.
The division of real power will be influenced by the phase shift, and the division of reactive power will be influenced by any voltage difference introduced.
As you said, somewhere, sometime.

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

 

[tinfoil]

@waross:
Have you ever looked up what happens in a phase-shifting xmfr (used at system intertie points)? It is essentially what you are outlining.

 

[prc]

tinfoil,you are right.Phase shifting transformers are used in Europe and US for intertie connection.There an OLTC is used in Zag winding to continuously adjust the angle of out put voltage.

In fact zig-zag earthing transformer is also such a connection eventhough the secondary is not taken out.In transformer engineers' bible- book by L F Blume etc- there is a chapter "Auto- transformer connections" by that GE Schenectedy guru A Boyajin.He is mentioning zig-zag,double zig-zag ,open zig-zag etc.Of course he is not mentioning phase shifting trfs because at that time the need for such a device was not there.

Normally with the connection mentioned by David with 1:2 voltage ratio the shift will be only +30 or -30 degrees depending on which phase is used as zag winding.How 120 lead will come?