Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!stiatl!rsiatl!jgd
From: jgd@rsiatl.UUCP (John G. De Armond)
Newsgroups: sci.electronics
Subject: Re: 50 Hz in Europe... Was the decision political?
Message-ID: <939@rsiatl.UUCP>
Date: 14 Dec 89 05:01:49 GMT
References: <2332@ektools.UUCP> <787@larry.sal.wisc.edu> <8973@cbmvax.commodore.com>
Reply-To: jgd@rsiatl.UUCP (John G. De Armond)
Organization: Radiation Systems, Inc. (a thinktank, motorcycle, car and gun works facility)
Lines: 38

In article <8973@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes:
>Actually, If I remember all this sillyness, for power equipment including
>motors and transformers lower frequencies are still cheaper because AC core
>losses (eddy current, hysteresis, etc), are lower allowing less complicated
>construction (thicker/few lamination) and less cooling. 
>
>Some of the major U.S. railroad electrification projects used 25 Hz for
>just this reason and were still using 25 Hz up to a few years ago, though
>the economies of custom power generation/converison had vanished with the
>advent of major power nets.
>
>Don't ask me why they didn't use 30 Hz...

Only true to a point.  True eddy current losses are less but because more
iron is necessary as frequency drops, the eddy current benefit is canceled.
When one cosiders that manufacturing trickery can reduce eddy current
loss to a very low value, the cost of increased iron is significant.
Another factor is that a larger core will require more copper for a given
amper-turns.  This will increase IR losses.  Nothing I can find in my 
library would indicate either frequency has a marked advantage.  Nor can
I find any reference to the use of 50 vs 60 hz.  I suspect that whatever
answer is postulated will contain a component of folklore.  It may
end up being something as simple as 50 hz sounds "metric" while 60 hz
sounds English.

25 hz electricity was used because slow speed motors can be build with
fewer poles than 60 hz.  This was important in railroad motors because
direct drive is considered important.  A much larger use is in steel
mills where VERY LARGE motors are constructed to run on 25 hz and to
drive rolling mill rollers directly.   There is a certain advantage
to eliminating gears on a 25,000 hp motor :-)

John

-- 
John De Armond, WD4OQC                     | The Fano Factor - 
Radiation Systems, Inc.     Atlanta, GA    | Where Theory meets Reality.
emory!rsiatl!jgd          **I am the NRA** |