Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!cmcl2!phri!roy From: roy@phri.UUCP (Roy Smith) Newsgroups: comp.misc Subject: Re: IBM mainframe for sale (Really 400/416 Hz power for Crays) Message-ID: <2953@phri.UUCP> Date: Wed, 7-Oct-87 11:31:56 EDT Article-I.D.: phri.2953 Posted: Wed Oct 7 11:31:56 1987 Date-Received: Sat, 10-Oct-87 10:53:14 EDT References: <4673@nsc.nsc.com> <2944@phri.UUCP> <365@nuchat.UUCP> <2952@phri.UUCP> <6424@apple.UUCP> Reply-To: roy@phri.UUCP (Roy Smith) Organization: Public Health Research Inst. (NY, NY) Lines: 45 In article <6424@apple.UUCP> bldrnr@apple.UUCP (Brian Hurley) writes: > The reason for a Cray using 400/416 Hz power has to do with the source > more than weight considerations. The amout of power used is very large > ([...] it may fall into the hundreds of KW) the only 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! Hogwash. Except for a very very few (experimental?) DC links, and some telemetry-over-power, *everything* on The Grid is 60Hz. Also, for an industrial site, a few hundred kW is just not that much. Our building, for example, (a moderate size light-industrial building in Manhattan) has two 6000 Amp, 120-Volt, 3-phase feeders. The feeders are not so much wires as copper bus bars running maybe 50 feet to a transformer under the street, which I believe steps down from the 13.8 kV sub-distribution. I suspect that 13.8 kV (if not higher) is available in just about any industrial park in the country. > Design a motor that works on 400Hz and have it drive a 60Hz Generator. > If the design is mechanicly sound, the losses are comparable to a > transformer of comparable size. This is true. Good power transformers and good M-G sets both have efficiencies on the order of 95%. Not particularly germaine, but true. I suspect there may be some confusion going on. It is common to find 3-phase, 240 Volt wiring in industrial plants. The 240 Volt reading is in Y configuration -- each phase to neutral. In a Delta configuration (i.e. looking at the phase-to-phase voltage) you get 417 or 416 Volts (depending on how you like to round off). Cables and panel boxes with 416 in them tend to be prominently marked with stickers reading "240/416" to distinguish them from the more common 120/208. Could it be that somebody saw one of these stickers and thought the "416" referred to the frequency instead of the Delta voltage? Somebody suggested the the M-G sets are there for electrical isolation, to provide mechanical inertia to ride over line transients, and to provide a simple hookup for an alternate power source (put a diesel on the same shaft as the M-G set, for example). All of these are reasonable explanations; saving weight in the transforer cores is not, at least not by itself. -- Roy Smith, {allegra,cmcl2,philabs}!phri!roy System Administrator, Public Health Research Institute 455 First Avenue, New York, NY 10016