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From: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Newsgroups: comp.misc
Subject: Re: IBM mainframe for sale (Really 400/416 Hz power for Crays)
Message-ID: <4843@sdcrdcf.UUCP>
Date: Wed, 7-Oct-87 00:01:54 EDT
Article-I.D.: sdcrdcf.4843
Posted: Wed Oct  7 00:01:54 1987
Date-Received: Sat, 10-Oct-87 07:13:32 EDT
References: <4673@nsc.nsc.com> <2944@phri.UUCP> <365@nuchat.UUCP> <2952@phri.UUCP> <6424@apple.UUCP>
Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Organization: Unisys - System Development Group, Santa Monica
Lines: 35

In article <6424@apple.UUCP> bldrnr@apple.UUCP (Brian Hurley) writes:
>In article <2952@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>>(or, as Jay says, 416) Hz.  Ditto for the noise and energy loss.  There is
>>nothing inherently wrong with big 60 Hz transformers; just walk out to your
>>nearest power substation and take a look.
>
>fall into the hundreds of KW)  the olny source for this kind of power
>is a Sub-station feed.  Which is NOT 60Hz. If you transmitted even 100KW of
>power @ 440VAC that would result in a curennt flow of approx 318 AMPS!
>Copper ain't that cheap! If I remeber my basic transmission line math, the
>higher the AC frequency, the smaller the transmission line needs to be,
>    -Brian
>/  UUCP: bldrnr@apple.UUCP   CSNET: bldrnr@apple.CSNET                        \
>\  ARPA: bldrnr@apple.apple.COM            voice @ 408/973-6679               /

I'm going to stay away from the trade off between MG set to 400 Hz and
smaller power supplies vs direct conversion to low voltage, but I suspect
there are significant advantages either way which come down to a judgement 
call by a Cray engineer.

Almost all of the nationwide power grid does run on 60 Hz, only voltage is
varied in most cases.  Power is a function of voltage times current, and is
nearly independent of frequency.  Generally, higher voltages are used for
carrying large amounts of power long distances (and as voltage goes up, so
does tower height).  Some highlines run at over a million volts).  DC is
actually superior for long distance transmission, but until relatively
recently, there was no efficent and reliable way to convert between ultra
high voltage DC and 60 Hz AC compatible with the majority of the power grid.
The original choice of AC for the grid was because of the easy
transformation of voltages.

-- 
Darrel J. Van Buer, PhD; unisys; 2525 Colorado Ave; Santa Monica, CA 90406
(213)829-7511 x5449        KI6VY        darrel@CAM.UNISYS.COM   or
...{allegra,burdvax,cbosgd,hplabs,ihnp4,sdcsvax}!sdcrdcf!darrelj