11 Mar
2023
11 Mar
'23
6:40 p.m.
On Mar 10, 2023, at 6:26 PM, Sytse van Slooten via
cctalk <cctalk(a)classiccmp.org> wrote:
True. I remember that the house where I grew up in Holland had 3 phase service because we
were one of the (then unusual) households to have an electric cookstove. It was fed off
380 volt 3 phase power.
But apart from circular motion (i.e., feeding motors) there is a second reason to use
three phase power: reduced ripple. Full wave rectification of n Hz mains power gives you
a 2n Hz ripple; full wave rectification of 3-phase n Hz mains produces a 6 Hz ripple, and
tha amplitude is a lot less as well. So the filters are much smaller, which is a
non-trivial matter if you need to filter several hundred amps. That of course assumes
your power supplies are actually fed off the three phase mains, rather than being
individual single phase supplies spread over the phases. The former was certainly the
case with the CDC 6600, you can see it clearly in the schematics.
paul
On Fri, 10 Mar 2023, Kevin Anderson via cctalk wrote:
Which machines needed 3-phase?
None that I am aware of - even the very power hungry 9021 'mainframes' I
mentioned earlier could be powered from a single phase, if you wanted to. The power
company might have expressed a view, but that's a different subject. 3 phase is
relevant to circular motion, not to the amount of power you need - although lots of
electrical equipment tends to come in 3 phase versions, especially if the amount of power
goes up.