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From: roy@phri.UUCP (Roy Smith)
Newsgroups: comp.misc
Subject: Re: IBM mainframe for sale (Really 400/416 Hz power for Crays)
Message-ID: <2952@phri.UUCP>
Date: Mon, 5-Oct-87 08:27:05 EDT
Article-I.D.: phri.2952
Posted: Mon Oct  5 08:27:05 1987
Date-Received: Thu, 8-Oct-87 05:47:49 EDT
References: <4673@nsc.nsc.com> <2944@phri.UUCP> <365@nuchat.UUCP>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 22

In article <365@nuchat.UUCP> jaym@nuchat.UUCP (Jay Maynard) writes:
> Have you considered just *how much* a Cray [...]  would weigh if they
> used 60 Hz power instead? Not to mention the hum from the massive
> transformer cores vibrating at 60 Hz, and the energy loss...

	Still doesn't make sense.  Surely the weight you get to save in the
cores is more than offset by the M-G set you need to turn 60 Hz into 400
(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.

	Aircraft use 400 Hz because saving weight is one of the most
important aspects of aircraft design.  They generate their own power, so
it's also no big deal to use a non-standard line frequency; they don't have
to interface to the power grid.  There must be something more than just
weight savings involved in the decision to use 400 Hz in a Cray.  For
Earth-bound machines, weight is just not that important; you can always
make the floor stronger.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016