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Tony Hwang

wrote:
In a current thread, gfretw told a poster that one
way to indentify 3 phase service is if it's connected
to two or three transformers. That brought back a
question that has stumped me for a very long time.

I know that it's possible to get 3 phase service with
just two transformers. Apparently that is used for cost
savings on lighter 3 phase loads. But what I don't
understand is how you can get true 3 phase with only
TWO transformers. Coming down the road you
have 3 high voltage lines. Each of those has an AC
waveform and each is 120deg off in phase from the
other. If you have three step-down transformers,
then you have one transformer connected to each
high voltage line and obviously you get 3 waveforms
out that have the same 120deg phase relation as
those on the high voltage side.

But how do you get 3 waveforms at 120deg shift
relative to each other with only two transformers
connected to only two of the 3 high voltage lines?

Hi,
I can see ut, it depends how the windings are wound and
how they are connected. I can visualize Delta 3-phase.