Re: Three phase rectifiers

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

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

Bob
Just several cautionary notes...

The "Delta" connected transformers (3) will have a turns ratio 1.732 times
higher on the secondary winding then the "Wye" connected transformers.
The reason for this is the Delta-Wye transformation to keep the two
transformers balanced kVA load wise. Any other ratio and you may get
destructive bucking (can you say "Let's let the magic smoke out of our
diodes!!! "   :^)    )

Also, be aware that the kVA to DC kW conversion factor with a 12 pulse
rectifier is considerably less then 0.6 (ie you need about 1.6kVA 3 ph
for each 1.0kW DC output).  I speak this from experience, having to build
a very high power low voltage linear regulated power supply (4kW to load
at 22V) for a separate R&D group...

Cheers, and regards!
Dave Sharpe, TCBOR
Chesterfield, VA. USA



Tesla list wrote:

> Original poster: "bob golding by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>
>
> Hi all,
>     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
>
> This should keep the ripple low enough to not need any filter caps. This
> will be safer and cheaper. I like safe and cheap in the same sentence.
> What voltage should I aim for for the piv on the diodes? peak voltage
> will be 16968V. If I go for the old rule for caps of 2.5 peak this works
> out at 42420V. I am planning to use IN4007's this works out at 42 diodes
> per leg x 12= 504. As they are only 8 pence each this is not a great
> expense. Less than £50.00. Is there a problem with long strings of
> diodes. If I get them all at the same time there is a good chance they
> will be from the same batch. Should I go for 3 amp ones instead? I know
> it is a lot of soldering. If it works I can fully exploit my variable
> speed async gap.
> cheers
> bob golding