RE: Cat's meow and 3-phase question was: Silly question?

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Original poster: "David Dean by way of Terry Fritz <twftesla-at-qwest-dot-net>" <deano-at-corridor-dot-net>

Hi David

> Now, I have a question about utility three phase transformer
> service that is bothering me and I was hoping some of the re-
> sident engineers could answer it  for me. I've read that a wye/
> wye three phase transformer hookup is rarely used by the
> utility power companies because of harmonics and balancing
> problems. However, virtually all of the three phase pole pig
> banks that I see in my local area (Memphis, TN) are hooked
> up exactly this way (all three phases sharing a common
> ground return on both the primary and secondary sides of the
> transformer). I was wondering if anyone could shead light on
> this for me?
>
> Sparkin' in Memphis, TN, USA,
> David Rieben
>
>
In the case of three separate transformers the cores are not magnetically
coupled.

In the case of a three phase transformer (pad mount with the primary fed
from underground) all three windings are on the same core, hence coupled
magnetically. You will find that the primaries are connected in delta in
that case.

later

deano