Saturable Reactors as Ballast

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Original poster: "Carl Litton" <Carl_Litton@xxxxxxxxxx>


Does anyone on this list have any experience building saturable 
reactors for ballasting purposes?  I found some older notes in the 
archive suggesting that a second winding on an iron core inductor can 
be used to introduce a variable DC voltage that will give full range 
control of the inductance as the core approaches saturation.

I have been able to demonstrate the effect on a small scale with a 
simple step down transformer by putting the primary in series with a 
120 VAC ciruit and connecting the the secondary to the rectified out 
put of a Variac.  A 2.7 Henry inductor  was reduced to a little less 
than 1 Henry with 140 VDC in the control winding, allowing a small 
light bulb just enough current to give off some visible light 
(measured current 0.188 Amp with no DC control and no light to 0.42 
Amp with 140VDC control and visible soft glow from bulb).

However, all attempts to do this on any large (20 to 250 lbs.) 
inductors controlling a 240 volt circuit in the 30 to 150 Amp range 
have been not only fruitless but have almost instantly slagged the 25 
Amp bridge rectifier connected to the control winding.

I need to understand what I am missing here.  Any theory or 
especially winding diagrams of working reactors would be greatly 
appreciated.  I did find one article that suggested 2 AC power 
windings in series and in phase have to be used with 2 DC windings in 
series and "out of phase" with each other in order to cancel the 
effect of induced AC in the control winding.  But here again, no 
practical application, turns ratios, winding configurations, etc.

Any thoughts?

Thank you,

Carl Litton

Memphis HV Group