Re: Three phase conversion In Rush current Concern.

["Tesla list" <tesla@xxxxxxxxxx>]

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