Don Murray wrote:



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

Don -
Sounds like you are in the trade. Guess you didn't see the canning factories bit.
Motors are three or more phase there.

They are 7, 9, 12, 15 - strange stuff. What that is all about is this :

Take your 'normal' three phase WYE or star then part way out on the arms re-direct the phase angle
and then sometimes redirect again the re-direct.

These smaller windings out on the end of the winding (in the circuit) are for shading coils on the
motors, coils, and other controls.

They have their energy in a different time domain as the main line coil. Lead or lag, they are
effective push or pull or pre-initialize and the like.

I have a ton of books to go through to find a twisted design - I thought my Motor repair manual
would have it - but didn't see it, then both electricians and electrical engineers standard handbooks
a quick glance - not yet...

I doubt my steam boiler engineering book has it or my High speed signal propagation boo, has. But it
was extracted once for my college notes and aided an electric company service man (a friend as well)
understand 3 phase with these nasty phases - more wires and binding posts than most.
The instructions stated that a single mis-wire would jam the machine. The pressure was on.

Martin

--
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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