"Leo Lichtman" wrote in message
...

"Robert Swinney" wrote: Leo, And your point is ?
^^^^^^^^^^^^^^^^^
If it's not clear, then I may be wrong about something. The OP was
proposing to raise power line frequency from 50 hz or 60 hz to 400 hz. It
looks to me like that would raise the inductive reactance and lower the
capacitive reactance of the network, both of which would be wasteful. If
that's not correct, straighten me out, please.



Regardless of the frequency, the laws of physics do not change. Power is
"consumed" (turned into heat, mostly) in a resistive load. And the IR
losses
will be the same (assuming the same voltage and current) regardless of the
frequency. There is no true loss due to reactance, only an opposition to
current flow. But, inductive and capacitive reactances are 180 degrees out
of phase with one another and, hence, if they are equal in magnitude,
cancel.
Thus, their contribution to the net impedence is zero; only the resistive
component has any effect on current flow and this effect is, of course,
minimized by using as high a voltage and low of current as practical. Now,
if the capacitive and inductive reactances are not equal, the dominant one
will twist the phase of the current with respect to the voltage and the
result
will be a loss of efficiency (a power factor of less than unity, to use the
buzz-
word...). So, the distributed inductance and capacitance of the
transmission
line become primary considerations of the engineer designing the line. And
the design will be different at different frequencies. But, in properly
designed
transmission lines, efficiency is independent of frequency.

This explanation is something of an over-simplification, of course. There
are
other things that come into play as the frequency goes up. But, at low
(power
line) frequencies, they can largely be neglected. (As one goes up into
radio
frequencies, things get complicated real fast...) And, of course, in the
trivial
case where the frequency is zero (DC), all of these concerns simply go away.

The bottom line is that, as the frequency goes up, the trickier the
transmission
line becomes.

Jerry