On Fri, 24 Mar 2006 18:03:12 GMT, "Lloyd E. Sponenburgh"
wrote:


"Don Foreman" wrote in message
.. .
Copper loss increases as square of current, further axacerbated by
increased resistance due to temp rise as noted.
Peak core flux density changes very little with load; it actually
goes down a bit with load due to IR drop in the primary. It is
determined by primary voltage and frequency. It it isn't saturated
under noload condx then it won't saturate under load. Core loss may
change slightly with core temperature, not sure how that works with
silicon steel.

Don.

1) I know the I^2R law. I said "more or less directly" because there are
several things that can change it, among them being the frequency of AC
being transformed, and interwinding/inter-turn capacitance. Even though
it's usually lumped together as "copper loss", it's not usually _only_ the
DCR of the wire they're accounting for in power transformers. They break
all that stuff out when spec'ing audio and RF transformers, but seldom
50-400Hz stuff.

2) Many transformers operate in rectifier circuits, and may have some DC
component in the secondary, as well as AC. Increasing the DC can indeed
induce saturation of the core. You know that.

(Prototypeing lab supervisor, Florida Transformer corp., div of Transitron,
1968)

Good point about rectification. I did forget about that, and that
would indeed be load-dependent. Thanks.