On Mon, 2012-04-23 at 07:43 -0700, Jim Thomson wrote:
> ## This is why you don’t toss out old Orr books. In the 19th edition, he
> shows
> 3 x different configs of hv supplies, all using 3 phase. The best one is
> called a
> 6 phase bridge, and uses 6 x legs of diodes. With just a tiny choke in the
> output,and
> NO hv cap at all, the ripple current is 4.2 %. Ripple freq is 6F or
> 360 hz.
The only gotcha is that that the 6 phase bridge needs two transformers,
both with the same secondary voltage, but one setup for three phase star
and one for three phase delta primaries (The phase shift between the two
provides the 6 phase output).
Of course the iron can be rated for only half the current which helps
(Or, one transformer with both star and delta secondaries set up to
produce the same phase to phase voltage).
Interestingly you still see this technology used in things like large
motor drives, plating supplies and the like, there is sometimes
something to be said for crude but effective.
You sometimes see this sort of thing referred to as 6 pulse (ordinary
three phase full bridge), 12 pulse (6 phase) and even (rarely) 24 pulse
rectifiers.
There were all sorts of clever circuits using heavy current inductors
developed back when a high power inductor was simpler and more reliable
then a suitably butch capacitor.
I have a fascinating hardback set of early books on electrical (there
was no such thing as electronic) engineering, some **really** far out
methods.
I second the comments on old books, Orr, Langford Smith, Terman, and the
rest it is all good.
> A 3 Phase plate xfmr + a 6 x phase bridge, and one small filter cap
> would be the ideal ticket.
Better, two three phase plate transformers each rated for half the
power, one setup for 230V star connection, and the other for 400V
delta, and a 12 pulse rectifier, gets you 600hz ripple (and much less of
it).
But remember for most of Europe, full legal limit QRO is rather less
then 1500W, (400W limit here in the UK, measured at the feedpoint), and
that can be rather easily produced without needing broadcast site style
power supplies.
Regards, Dan.
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