Re: Three phase rectifiers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Greg Leyh by way of Terry Fritz <twftesla-at-uswest-dot-net>" <lod-at-pacbell-dot-net>

>     I have worked out the wiring for my 3 phase rectifier design. I am
> going for a design voltage of 12kv at 1 amp. I would like some feedback
> on the best way to go about choosing the diodes. I am going for the 12
> pulse recifier design shown here (scroll down the page)
> http://ham.te.hik.se/homepage/sm5bsz/supply.htm


Yes, it's a good idea to get them all from one batch.  Each
diode should have an RC snubber ckt around it, as well.  I'd
splurge for the 3A diodes though, since there will be a lot
of current spikes from parasitic effects at those voltages,
and from the unballasted filter cap shown, at startup.

A 12-pulse system would be very nice, indeed.  A 6-pulse set
produces too much ripple, I assume?  I'm totally envious of
the /standard/ 3-phase mains, that European households enjoy!

One item that might be problematic in the circuit is the 
wye-connected primary set.  Normally, 3ph power xfmrs are
connected delta-delta or delta-wye, since wye primaries have
a tendency to launch heavy 3rd harmonics onto the neutral... 
especially when there is an un-ballasted cap right after 
the diodes.  There is also the possibility in a wye-primary
of intermittent core saturation events, unless the neutral 
has a /very/ low impedance.  This will be evidenced by the 
main breaker tripping randomly when power is applied, and 
substantial overvoltage spikes at the DC output.

You mentioned that there are two types of xfmrs in the 
circuit.  I assume that means they have different turns
ratios... one for the delta, and one for the wye?
---


-GL
www.lod-dot-org