RE: Saturable Reactors (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 4 Jan 2006 11:45:21 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: RE: Saturable Reactors (fwd)

Thanks to you, Dave, and to all who responded on this question.  The
explanation makes perfect sense and was put to the test immediately.

A 20 lb 3-leg wide-window transformer was converted to a saturable
reactor in which the center leg was the power winding (278 mH) and the
outer two windings were the control windings, which were placed in
series such that no voltage was induced in them when the center winding
was energized.  0-25 VDC into the control winding series gave full range
control of the inductance of the power winding with no heat or other
negative effects!!!  Thank you!

We are now constructing a large S.R. (180 lbs.) in the opposite
configuration - 2 power windings in series on the outer legs and 1
control winding in the center.  This is being done using what was
originally a shut transformer that was built to handle over 200 Amps.
This should provide an extremely versatile adjustable ballast for almost
any project.  

[And in it's off-time, at 180+ lb, it would serve as one heck of a
doorstop!  Not all good things come in small packages.  SRR]

Thanks again,

Carl 

-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Tuesday, January 03, 2006 8:46 AM
To: hvlist
Subject: Re: Saturable Reactors (fwd)

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