Saturable Reactors Was: Strange Choke

To: tesla-at-pupman-dot-com
Subject: Saturable Reactors Was: Strange Choke
From: Tesla List <mod1-at-pupman-dot-com>
Date: Mon, 20 Oct 1997 09:50:17 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Mon, 20 Oct 1997 09:13:24 +0500
From: "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Saturable Reactors  Was: Strange Choke 

On Sun, 19 Oct 1997 13:25:56 +0100 Gwyn Zucca
<gwyn-at-tcbod.demon.co.uk> wrote;
> Hello All,
> 
> Thanks to those who replied to the mail I posted about current limiting
> power transformers. On the same subject I have been given a transformer
> unit which looks like it was designed as a variable choke. It has four
> terminals on the connection plate, two of these are marked AC and the
> other two DC. The unit is wound on a single bobbin, but the cores are
> double C cores and probably air gapped internally. I have not yet
> measured the inductance of the windings, I assume that these sort of
> units would use a DC current applied to the DC winding to vary the flux
> field, and so control the AC current flowing in the AC winding. As I
> have not seen one of these chokes before I wondered if any body else
> has, and if so does any one have any experience with them.

It sounds like you found yourself a saturable reactor or magnetic amplifier 
as they were sometimes called. See the ASCII drawing below.

                           D.C.
                            +
              ______________|________________
             |              |                |
   A.C______ |     ______   |    ______      | ______ A.C.
            )|    |      |  )   |      |     |(
            )|    |      |  )   |      |     |(
            )|    |      |  )   |      |     |(
            )|    |      |  )   |      |     |(
            )|    |      |  )   |      |     |(
            )|    |______|  |   |______|     |(
            ||______________|________________||
            |---------------|-----------------|
                            |
                            -
                           D.C.

Equal turns in the A.C. coils set up equal magnetic forces which cancel in 
the center leg. No A.C. voltage is induced in the D.C. coil, but D.C. flux 
flows in both outer legs. A change of current in the D.C. coil causes a 
change in total flux linkage in the A.C. coils and hence a change in 
inductance. Since the core has NO AIR GAP, wide changes of inductance are 
obtained. The A.C. coils may be connected in parallel instead of in series, 
provided equal turns in each coil and the flux polarity are maintained; for 
the same total number of turns the inductance is halved and the alternating 
current doubled.

                               Sincerely

                                \\\|///
                              \\  ~ ~  //
                               (  -at- -at-  )
                        -----o00o-(_)-o00o-----
                           Alfred A. Skrocki
                   Alfred.Skrocki-at-CyberNetworking-dot-com
                             .ooo0   0ooo.
                        -----(   )---(   )-----
                              \ (     ) /
                               \_)   (_/