On Thu, 12 May 2011 16:13 -0600, "Robert Rolf" wrote:

> I may be dense, but how does drawing current for only a half cycle=20
> result in DC in a transformer so as to shift the flux operating point to=
=20
> where is may saturate? I see it as being no different (flux wise) than=20
> running the transformer with current in both directions. The flux STILL=20
> gets to zero at twice the mains frequency. With half cycle use, it just=20
> never gets to see much reverse flux. So what?

If it is only once it isn't a problem. If you load it asymmetrically,
the loaded phase has lower flux density. The result is a net DC flux.
With cores that are not fabricated for any DC bias, you lose inductance
and the core saturates at a much lower flux. Plus the flux is higher on
the unloaded phase because the voltage will be unnaturally high.
=20
> Which goes back to my original question, why is 1/2 cycle power=20
> utilization a bad thing? How does it create problems in a transformer,=20
> given that it IS NOT steady state DC which would shift the flux=20
> operating point?

A little bit is OK. So the 250 watts a work light draws in "low" is fine
on a 200 kilowatt pole pig transformer. Too much will make heat, and
draw current with nasty power factor.

Cheers,

Bob

--=20
http://www.fastmail.fm - Choose from over 50 domains or use your own

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.