SCADA (was Re: Help to identify a computer?)
ard at p850ug1.demon.co.uk
Sun Feb 18 20:07:25 CST 2007
> On Sun, 18 Feb 2007 22:46:57 -0800, Brent Hilpert wrote:
> >"In even later years, solid-state rectifiers of sufficient capacity for the
> >traction power industry were developed, and substations became no more
> >exciting than giant computer chips."
> Now there are fighting words. I expect this group would find a giant
> computer chip of great interest !
I don't find large chips to be of much interest. Now large boards of
small chips are a differnt story :-)
> Thanks for the subway link, and to keep things on topic, the IBM 370
> family of mainframes used a MG
> (motor genertaor) set to convert the 60hz power from the mains to 3
> phase at 400Hz to allow more efficent
> conversion of power in the internal supplies. Both smaller
> transformars and much smaller filter caps were
> needed to convert and smooth the 400hz to DC.
I believe (military?) aircraft used 400Hz-ish supplies because they could
then use smaller (and lighter) transformers and smoothing capacitors. It
can be a problem for the military radio enthusiasts who want to power up
such sets now.
And of course it's one advantage of the modern SMPSU. The transformer is
much smaller than a 50Hz (or 60Hz) transformer of the same output
ratings, and the smoothing capacitors are smaller too.
> In fear of sliding too far back on topic :-)
> I will point out that the telephone system uses 90v 30hz as the ring
> signal because it worked so well with
> the mechanical bells used in the early phones.
Over here I think it's officially 25Hz, but for much the same reason.
Medium and large telephone exchanges produced that supply using a
motor-generator set running from the (50V DC) lead-acid battery that
powered the rest of the exchange. Small private exchanges produced it
from the mains using a resonant transformer/capacitor circuit fed with
half-wave rectified mains (I have one of the ex-GPO converters somewhere).
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