Re: Alternators Re: phase conversion

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: dave pierson <davep-at-quik-dot-com>
 >
 >  >>> why not just have a large electric or gas motor run a homemade 3 phase
 >
 > > > alternator? getting the rpm's right for 60 hz might be a bit tricky, but
 > > > it'd work even if ineffecient.
 > >
 > >It's a little more complicated than that.  I have already built such a 
unit.
 > >It's been nearly a year, so I don't remember the details, but it only put
 > >out something like 2 volts.  Something has to happen inside the alternator
 > >to get the magnetic field built up properly.  Someone told me to put a DC
 > >current over one of the legs for a minute or so to kick start the magnetic
 > >field, but that didn't work either.
 >
 >     ??
 >
 >     An alternator, as such, has a rotor, which must be powered with DC,
 >     or, for small, units, a permanent magnet rotor may be used.
 >
 >     'putting DC into one of the legs' is strange.
 >
 >     An _induction alternator_ is a separate beasty, which requires
 >     external AC excitation.
 >
 >     best
 >      dwp

	An induction generator will operate with a load of suffiently negative
power factor, but not sure how it gets "started" without external
excitation.  The common use is to have the generator across an operating
line and use it to supply power to that line, often for regenerative
braking.  I've been told by someone who should know that a number of
elevators have been operated that way.  When feeding a line which
already has power on it the lead angle of the generator takes the place
of the capacitive load.

Ed