On Thu, 22 Dec 2005 20:36:17 GMT, "daestrom"
wrote:


"Roger" wrote in message
.. .
On Wed, 21 Dec 2005 14:29:00 GMT, Matt Whiting
wrote:

George Ghio wrote:

Tell us why anyone would modify a sine wave.

To vary the power delivered to a load. Chopping off part of a sine wave
cycle is a standard means of power control.


That makes three phase SCR (Silicon controlled rectifiers and not
saturable core reactors) interesting as chopping off part of the wave
form develops spikes and harmonics that tend to make the control of
one phase interact with the others.

I've built a lot of them for single phase control, but I never once
was able to build one for three phase that didn't interact. Turn one
up and maybe another would go up, Turn the second down and the other
two might go up or down. Twas interesting:-)) which is probably why
Saturable core reactors are so popular in industry. Now there is a
controller that is a tad on the weighty side.


Also, some old systems used self-saturating reactors (magnetic amplifiers,
'magamps') for instrumentation. Things could take some severe environments,
but calibration tended to drift a lot. Required fairly frequent 'trip &
cals' to keep them in spec.

For the small and large stuff we used solid state SCRs while the
intermediate still used saturable core reactors. 10 years ago I think
they still had some mag amps, but the ones we had were pretty stable.

They use larger SCRs now, but I have the silicon wafer out of one that
is over 1 1/2" in diameter. They operated up to 480 and 1000 Amps
and ran near maximum for many hours. The SCRs themselves were about
the size of a hockey puck or slightly larger.

Now there was some power and I'd guess they use much larger systems
now.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

daestrom