Re: Transformer Ballasting

To: tesla-at-pupman-dot-com
Subject: Re: Transformer Ballasting
From: Tesla List <mod1-at-pupman-dot-com>
Date: Sun, 19 Oct 1997 21:38:54 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Sun, 19 Oct 1997 12:42:14 +0500
From: "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Transformer Ballasting 

On Thu, 16 Oct 1997 19:43:35 +0100 Gwyn Zucca
<gwyn-at-tcbod.demon.co.uk> wrote;

> Hello All,
> 
> I have tried searching the list archives for anything on the subject of
> current limiting power transformers, but I did not find exactly what I
> was looking for. The problem seems to be limiting the short out current
> without reducing the output voltage of the transformer. Obviously any
> resistance in circuit with the xfrm primary is going to develop a volt
> drop across it, and so the primary voltage will be lower than the rated
> output. The use of an inductive ballast, is going to have a similar
> effect. I have been experimenting with various arrangements, but have
> not yet achieved a satisfactory solution.
> 
> Any thoughts, experiences on this subject would be welcome.

Your observations are correct in that any resistive method of current 
limiting a transformer is going to cause IR^2 losses. The traditional 
approach is to use an inductance or choke to current limit the transformer. 
Many of us use arc welders with the outputs shorted to control pole pigs. 
On commercial bombarder transformers they use either a variable choke ( a 
bar of iron laminations that slides in and out of a large coil) or they use 
a saturable reactor. A saturable reactor is essentialy a transformer with 
its primary and secondary in series and a third winding is added on the 
center leg that is fed with D.C.  Effectively as more D.C. is applied 
the effect of the center leg of the transformer is neutralized and the 
inductance of the primary and secondary windings goes down. Presently 
saturable reactors or magnetic amplifiers as they are also sometimes called 
are a cut and try affair.

                               Sincerely

                                \\\|///
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                           Alfred A. Skrocki
                   Alfred.Skrocki-at-CyberNetworking-dot-com
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