On Thu, 22 Dec 2005 03:10:59 GMT, Matt Whiting
wrote:

Roger wrote:
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.

The application I'm familiar with (well I was 10 years ago) was
electrically fired glass melting units. The resistive load didn't much
care about cross phase interference. :-)

The ones I'm referring to were large ovens with, I'd presume,
resistive elements as well. I finally gave up and purchased a
comercial unit.

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

Matt