Ugly ? - add another transformer and you have true 100% power 3 phase.

With two - and that two gave you three phase and split 220 as well.

So it used the center tap on the right side If split 22O came from
the house on the underground - and the three phase from the pad
transformer, then only three secondary wires are used.

The Military and police/fire all use Three Phase. Delta-Delta.

The idea - overrate the transformer by at least 1/3 but normally 1/2.
Then if or when worse comes to worse, and an input leg is lost, or
a winding is lost (bullet...) the secondary can continue at ~66% e.g.
100% of wanted (due to overrate.) They could take a hit on the primary
and secondary and still stay alive.

Martin

On 10/26/2010 3:42 PM, Jim Stewart wrote:
john wrote:
Jim Stewart wrote:
John wrote:

With 208 single phase two pole transformers were needed, and if three
phase were required you needed to install three transformers to obtain
the star or wye configuration. By using the center-tapped transformer
neutral transformer it eliminated a second transformer. If three phase
was required it was necessary to add only one more transformer rather
than two, except when higher power rating were required and a third
transformer is used. That was the difference between open leg delta and
a full delta secondary. A lot of people are confused by seeing only two
high voltage primary wires and getting fed with three phase into their
building but that is very common.

Do you mean 2 high voltage wires or 2 transformers?

Three phase is possible with 2 transformers, but not
with 2 high voltage lines.



Three phase can be had off of two hi voltage primary wires.
It is just that you have no choice but to go open delta on the lv.

Yuck. You're right. But you do have to have
a neutral referenced to the hv wires.

http://blog.allshookup.org/wp-conten...-schematic.png


What an ugly kludge. I'm surprised anyone
would use such a thing.