Wye transformer phase shift

[bdn2004]

I am reading different specifications for the same 345 MVA, 20kV-145kV, delta(20kV), wye (145kV) step up transformer. One is from a recent purchase, the other is for a purchase we are to make within the next few weeks.

I notice that one calls for the lower voltage vector to lag the high voltage vector by a phase angle of 30 degrees. The other calls for the high voltage vector to lag the low voltage by 30 degrees - exactly opposite.

Do these specs match?

 

[davidbeach]

NO! ANSI standard is that high side leads low side. The IEC world doesn't seen to have a standard. The output of the two transformers will be 60 degrees out and certainly can not be paralleled.

 

[ScottyUK]

We don't have a standard? Isn't all the phase information included in the vector designation (e.g.) YNd1, Dyn11, etc? Lead or lag information is in the number. Do your clocks sometimes run backwards over there?

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If we learn from our mistakes I'm getting a great education!

 

[dpc]

Agree, but see this:

faq238-1154

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[bdn2004]

Thanks for the post. These transformers are stand alone units that will not ever be paralleled. One could replace the other however.

If the leads were swapped on the low voltage side what would that do to the phase angle? A-phase is connected to C, C to A?

 

[davidbeach]

What I meant, Scotty, is that we don't need no stinkin' vector designation, high leads low by 30[°]. Always. ;-) Except when it doesn't, and when it doesn't somebody had to have had a very good reason, or they just hooked a transformer up wrong.

On the other hand, as dpc's link leads to, you can take a DY transformer, either a DAB or a DAC, and get any odd multiple of 30[°] as your phase shift. Had a good reason once that I wanted the low side to lag by 90[°] rather than 30[°], so line crew and wiremen went to work swapping things around on both sides and a Dyn1 became a Dyn3. Good thing the core positive and negative sequence impedances are the same since the core went from an H1-H2-H3 rotation to an H1-H3-H2 rotation.

 

[ScottyUK]

"Always. Except when it doesn't" is the kind of logic my wife uses.

I'd forgotten about the FAQ dpc, thanks for the reminder.


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If we learn from our mistakes I'm getting a great education!

 

[dpc]

And thanks to stevenal for writing it.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg