Martin H. Eastburn wrote:


Your one high voltage (really medium or somewhat low for service) is a
single phase
of a larger 3 phase system.
7200V phase to ground is one leg of a 3 phase 15KV system, which is
about normal. There is older 4160/2400 primary and there is also higher
voltage primary. We operate a 20.8KV system that's 12KV phase to ground.



It is used to drive a input of a transformer - the other side is earth
ground.

His 7200V transformer would be a phase to ground, but the other side
isn't just grounded, it is either hooked to a primary neutral or most
likely a common neutral. Both are metallic returns to the substation,
both are grounded at the substation. Common neutrals are common to the
primary and the secondary and have 3.5ohm grounds or less every 1000'
under the main line and at the end of all taps.


There are unique
transformers that
can generate twisted star voltages and phases but the are not at homes.
(Canning factories yes...).

Show me a twisted star. This one pegged my BS meter.




Martin

Don