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In article <726@neoucom.UUCP>, wtm@neoucom.UUCP (Bill Mayhew) writes:
> I have done some work on power distruibution systems-- though not
> too much.  Most 400 Hz stuff is designed for use in mobile
> applications where saving weight and size is very important.

	Interestingly enough, frequencies higher than 400 Hz have been
used to power aircraft equipment.  While 400 Hz is now the standard,
much experimentation was conducted during World War II.
	Based upon the design and manufacturing capability that existed
during WW II, a weight savings of 50% in transformer "iron" could be
achieved by going from 60 Hz to 400 Hz.  While toroids represent an even
higher weight savings at 400 Hz, toroidal manufacturing was extremely
limited during WW II.
	Frequencies higher than 400 Hz were tried, but with diminishing
returns.  Going from 400 Hz to 800 Hz produced only 10% reduction in weight.
Nevertheless, 800 Hz was pretty much adopted as the standard frequency for
U.S. Navy aircraft during WW II.
	Stable power frequencies could only be produced by means of a DC
powered inverter; it is obviously impossible to produce a constant frequency
by an alternator that is directly driven by an aircraft engine.  However,
to "keep things simple", engine-driven alternators were indeed used on
some WW II aircraft; they produced a constant voltage (carbon pile regulators
no problem here), but a variable frequency.  Common frequency ranges used
were 400 to 800 Hz and 800 to 1,600 Hz for U.S. aircraft; the British went
one step further, they used alternators which went from 1,200 to 2,400 Hz.
That's right - 2,400 Hz 3-phase power!
	The philosphy with variable frequency AC power was to use small
inverters for frequency-critical power like servomechanisms.
	With some hindsight, there was probably no practical advantage
in using frequencies above 800 Hz, but a lot of "strange" things were
done during WW II.  Frequencies higher than 400 Hz did carry over into
the 1950's, but by the 1960's 400 Hz remained as the survivor.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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