Does anybody know why 25Hz, anyway? 60 Hz you can sort of see from 60 seconds to
the minute. 50Hz gives some convenient motor speeds like 3000, 1500, and 750.
(2, 4 and 8 pole machines)
The 16-2/3Hz that Johan mentions is also used on Belgian railways, (possibly
others, too) although at 3300volts. I suspect there could be some sort of
relationship to the Ganz 3 phase system of railway electrification (2 overhead
wires and track return). It also provides a lower motor speed, requiring lower
gear ratios. At one time, I believe, London theatres had 25Hz and DC provided. I
can just about see why the DC, but not the 25Hz.
Considering the amount of iron needed, what was the advantage of the lower
frequency? Eddy current losses because laminations couldn't be made thin enough?
73
Peter G3RZP
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