Wye-Wye Grounded Transformer Help

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?s falke

My former employer, AEP, often used wye-wye padmounted transformers. It was the "normal" three phase padmounted transformer configuration for wye services (120/208 and 277/480). Every transformer connection has positive and negative characteristics. What are you concerned about?

Charles Perry P.E.

There are a couple of instances I've heard of locally where the utility has used Y-Y solidly grounded for 24940/14400V:customer transformers. So maybe it's not "that bad"? One thing about Y-Y is that it would not stop the zero sequence components. Stopping zero-seq components would, I guess, be good for having less fields associated with your lines (lower field levels for public concerns, telephone interference, etc.), and as a bonus you filter a lot of your pesky 3rd and 9th etc. Maybe it's good under fault conditions, too, because I guess you could cause some grief if you ship 10kA of zero-seq

60Hz a few miles across town. Utilities may also be concerned about sequence impedances for their capacitor switching operations. Maybe they just generally prefer to run around with 3P 3W and avoid the cost of a fourth wire, so D-Y just makes sense. Can you call your local utility and ask to talk to someone in transmission&distribution engineering?

By the way, if that's your real email address you may want to 'disguise' it a bit when posting or you may be getting a lot of junk email.

Good night.

j

third harmonics. Often a Y-Y -delta is used (particularly for large transformers and autotransformers. The delta provides a 3rd harmonic current path so none flow in the lines.

Granted, but would you expect to see a tertiary on a low voltage transformer like that? A transmission service transformer, yes.

I would have expected to see DY 4W at that voltage - that would be going right into houses, wouldn't it?

This is interesting, because I'm learning about this, too.

HR

From what I can tell, Wye Wye is the most common connection for such transformers (medium voltage to low voltage).

Charles Perry P.E.

This will raise some disafreemtnent, but The choice of wyt over delta in MV>LV distribution transformers tends to be very regional. A better-than-average thread for distribution applications is

?s falke

Nice link. I don't disagree. The choice is regional. I would contend that in the US, Wye-Wye is probably more common (it is the standard for many of the larger utilities anyway).

Charles Perry P.E.

| Nice link. I don't disagree. The choice is regional. I would contend that | in the US, Wye-Wye is probably more common (it is the standard for many of | the larger utilities anyway).

All the commercial building pole pig banks around here (AEC) I see are YY. But I have no idea whether it's done that way because the engineers want it that way, or because the pin heads want it that way.

Hello, all. The most widely used MV/LV power distribution system in the U.S. appears to be the 4-wire multigrounded common neutral system. Among other things you only need to have one MV primary bushing, one lightning arrestor, and one fuse/fuse cutout rather than two on each distribution transformer. For commercial (non-residential) applications, the 120/208 (secondary side) wye-wye connection using three transformers is the most common. Sincerely,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337

| On Wed, 26 Jan 2005 10:28:48 -0500 Charles Perry wrote: | | | Nice link. I don't disagree. The choice is regional. I would contend that | | in the US, Wye-Wye is probably more common (it is the standard for many of | | the larger utilities anyway). | | All the commercial building pole pig banks around here (AEC) I see are YY. | But I have no idea whether it's done that way because the engineers want it | that way, or because the pin heads want it that way.

I take that back. I do see a few double bushing pole pigs around in three phase banks, and there are obvious bushing to bushing wires, so it looks very delta to me.

But what is the secondary connection?

Charles Perry P.E.

|> | On Wed, 26 Jan 2005 10:28:48 -0500 Charles Perry |> wrote: |> | |> | | Nice link. I don't disagree. The choice is regional. I would |> contend that |> | | in the US, Wye-Wye is probably more common (it is the standard for |> many of |> | | the larger utilities anyway). |> | |> | All the commercial building pole pig banks around here (AEC) I see are |> YY. |> | But I have no idea whether it's done that way because the engineers want |> it |> | that way, or because the pin heads want it that way. |>

|> I take that back. I do see a few double bushing pole pigs around in three |> phase banks, and there are obvious bushing to bushing wires, so it looks |> very delta to me. |>

| But what is the secondary connection?

I'll have to go look again. I'm seeing both wye and delta, but most of the delta seems to be on older services.

Around here most pigs are wired YY. One utility often wires the primary of 3 phase service delta even when single phase service is 1 bushing Y. Secondary is nearly always Y, with a few older delta. A few older circuits have every primary wired delta.

Aside: In several places I noticed that on older services with secondary wired delta the pigs are mounted side by side on crossarms rather than in a triangle on the pole. Was this some sort of industry practice to do this for some reason?