Re: Saturable Reactors (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 23 Dec 2005 11:17:21
From: David Dameron <ddameron@xxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Saturable Reactors (fwd)

Hi Carl,
It is important to do the phasing. It can either be on the power or control
winding. It removes two problems:
1) The effect of AC being fed into the output of the DC control supply. Can
your DC supply handle this?
2) The DC supply acting as a short to the AC in the control winding, thus
reducing the power winding impedance or reactance.

One example is a E-I core with center leg 1.5 x 1.5 inches.
The laminations are interleaved.
On the center leg, 1000 turns No. 30 AWG. this is the control winding.
On each of the 2 outer legs: 100 turns No. 18 AWG. These are the power
winding and connected in series so the AC induction in the control winding =0.
The power winding is connected to 120VAC, 60 Hz and the load in series.
Draw the flux lines in the core to see how it works.

The "Electronics Engineers' Handbook" used to have a large section on
saturable reactors and magnetic amplifiers. Haven't gone through some of
the millions of Google responses.
-Dave D.


At 09:18 AM 12/23/05 -0700, you wrote:

>Does anyone (Doc, Peter, Jim, etc.) 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 thougts?
>
>Thank you,
>
>Carl Litton