Re: Spawning a 12 pulser

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I think the advice is more aimed at distribution transformers, where you
don't have as much control over the load side.  Check the North report.. he
has a bunch of info about various rectifier schemes and distribution
problems or lack thereof.

The usual advice is that wye wye connections wind up with regulation (read
voltage drop) problems, because of unequal distribution of currents in the
legs.  They use a device called a "neutral forming" or "Z winding"
transformer to fix it (also can be used to form a Neutral on a delta
connection). 

Someone posted a link on power factor correction recently on the beowulf
list (in connection with running many PCs off three phase Y connected power
(120Y/208)) and that site had a great explanation of the source impedance,
harmonic current, and so forth, problems that arise feeding capacitive
input filter/rectifiers off three phase power.  It had a good discussion of
low and high harmonics, etc.


http://www.mirusinternational-dot-com/pages/q&a_fr.html is the link... 

Tesla list wrote:
> 
> Original poster: "Finn Hammer by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<f-h-at-c.dk>
> 
> Guys!
> 
> I decided that, since this is perhaps going to be the last transformer
> that I wind, (in these fast moving OLTC days :o)  ) I would be a
> complete a**, if I did not wind it to conform with a 12 pulse supply,
> even though I have quite a few questions about it. I`l take one at a
> time.
> 
> Looking at this link:
> 
> http://www.elec-toolbox-dot-com/usefulinfo/xfmr-3ph.htm
> 
> I am informed, that it is a bad thing to run a 3-phase transformer in
> WTE-WYE mode. That means connecting both the primary windings as well as
> the secondary windings in WYE, or "star" as we say overhere, due to
> problems with "harmonichs" and balancing.
> 
> The 12 pulser transformer has secondaries connected in both WYE as well
> as Delta, so taking the advise seriously would mean, that I am
> restricted to connecting the primary in Delta.
> 
> This is not a bad thing all together, but I would get a more versatile
> transformer, if I could also hook the primary in WYE, so I need to ask:
> 
> Does anybody here know, what these harmonic and balancing problems
> really mean, can it lead to runaway conditions, is it a serious problem
> or just some theoretical nitty gritty?
> 
> Cheers, Finn Hammer