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RE: Three phase conversion In Rush current Concern.



Original poster: "Leigh Copp" <Leigh.Copp@xxxxxxxxxxx>

And in fact this is a variation of an open delta configuration, which is
a documented method for using two single phase transformers for three
phase operation. A motor -is- a transformer after all.

Leigh

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: September 30, 2006 8:11 PM
To: tesla@xxxxxxxxxx
Subject: Re: Three phase conversion In Rush current Concern.

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Now, in reality, it's not quite that bad, because once the LOAD motor
come up to speed, it acts as a rotary converter itself.  In fact,
this is a real problem with fusing/overcurrent protection for three
phase motors.  Once running, you can disconnect one of the phases and
it happly keeps running as a single phase motor, but dissipating a
LOT more heat in the one remaining winding."

    When I was going to college one of my EE profs at the U of Mo
told a story from his days as a young engineer, not long after
WW1.  He was involved with a mine which ran a lot of stuff of a three
phase line and the bottom line to his story was that there was a very
big blower running from the power line and a lot of small loads.  One
day a truck knocked down a power pole and one of the three lines was
pulled in two.
When it was restored none of the motors would run.  Turned out the
explanation was that one of the other phases from the substation had
been open for a long time, probably many years, but the big motor had
been operating the other loads as a single phase to three phase
converter.  Restoring all three lines brought all back to normal and
it was noticed right away that all of the motors ran better!  Extreme
example of first sentence but probably has happened often enough.

Ed