RE: SUCCESS with Saturable Reactor from MOT's (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Thu, 2 Mar 2006 10:30:44 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: RE: SUCCESS with Saturable Reactor from MOT's (fwd)

Hi Malcom,

We have found this very interesting since it was first suggested by
another list member.  We have since found that this idea is quite old,
having been written and published through multiple sources in the public
domain years ago.  Yet another list member was kind enough to forward
some old industrial spec sheets that depict the different magnetic
arrangements that can be used for these 'parametric transformers,' as
they are called, including the 2-core type used here.

This type is called a saturable reactor with **voltage** cancellation as
opposed to a saturable reactor with **flux** cancellation, which is the
more familiar type involving a single core.  Please forgive if you
already know this.  The point is that you are exactly right in that
phasing is all that is involved with this type of 2-core arrangement.
With the secondaries connected in opposing series, the primaries must be
connected in such a way (either series or parallel) that the secondary
voltage is cancelled.  If the phasing is not marked on the transformer,
one simply tries one type of primary connection and tests to see if
there is voltage in the secondary series.  If not, you are done.  If so,
then one pair of primary leads is swapped to effect the cancellation.  

The 'correctness' of a given drawing is actually based on the winding
'sense' of the transformers involved, and as such, it may be of lesser
importance than noting on the drawing that wiring should be preformed
such that the secondary voltages will cancel and carrying out the
necessary testing to insure that this happens.

Carl Litton



-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Wednesday, March 01, 2006 3:39 PM
To: hvlist
Subject: Re: SUCCESS with Saturable Reactor from MOT's (fwd)

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 1 Mar 2006 16:47:56 +1300
From: m.j.watts@xxxxxxxxxxxx
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: SUCCESS with Saturable Reactor from MOT's (fwd)

I have to admit I'm struggling to see the difference between the two 
circuits. As long as each pair of transformers have the control 
windings oppositely phased it should work shouldn't it? A nice idea 
indeed. Reminds me of hybrid telephony circuits in a way.

Malcolm

On 28 Feb 2006, at 7:30, High Voltage list wrote:

> Original poster: Steven Roys <sroys@xxxxxxxxxx>
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Fri, 24 Feb 2006 07:17:48 +0100
> From: Finn Hammer <f-h@xxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: SUCCESS with Saturable Reactor from MOT's (fwd)
> 
> Carl,
> 
> Congratulations, this may be the most important discovery in quite
some 
> time.
> 
> I may be wrong, but from the schematic, it would appear that you have 
> the secondaries wired in parallel pairs of opposing series, as you
describe.
> However, since the primaries are wired in pairs of opposing parallel,
it 
> would appear to me, that the effect is canseled, and you would in fact

> get voltage on the secondaries/controll windings.
> Therefore I suggest that the schematic does not faithfully record the 
> setup as you describe.
> Perhaps this is more what is intended?
> http://home5.inet.tele.dk/f-hammer/satur.jpeg
> 
> However, a very clever idea. I have never seen anyone taking the 
> controll winding out on 2 separate cores.
> 
> Cheers, Finn Hammer
> 
> High Voltage list wrote:
> 
> >Original poster: Steven Roys <sroys@xxxxxxxxxx>
> >
> >
> >
> >---------- Forwarded message ----------
> >Date: Wed, 22 Feb 2006 08:55:34 -0600
> >From: Carl Litton <Carl_Litton@xxxxxxxxxx>
> >To: High Voltage list <hvlist@xxxxxxxxxx>
> >Subject: SUCCESS with Saturable Reactor from MOT's
> >
> >The following is cross-posted between the 2 lists since we think it
will be germane in both arenas:
> >
> >
> >In our research into different types of ballast to control current
demand on various projects, w
e found that it is often useful to be able to vary the current
independently of the voltage if a si
ngle power supply is to be used for multiple projects with different V
and I requirements. In the p
rocess, we ran across the concept of the Saturable Core Reactor.  The
idea is simple.  Introduction
 of a small variable DC voltage into a separate winding on an iron frame
inductor will bring the co
re to saturation, opposing the inductance of the power winding.  The
closer to saturation the core 
becomes, the lower the inductance of the reactor and the larger the
current that is allowed to flow
.   We find this concept intriguing because it offers infinitely
variable control of large currents
 by way of a low power control circuit.  We have conducted several
experiments on this subject and 
will publish a comprehensive article when all of the data is in.
However, our most recent experime
ntal configuration has given such remarkable results that we find it
worthy of being reported separ
ately.  
> >
> >One of the major drawbacks to creating a saturable reactor from
scratch is the requirement that 
the control winding consist of 10-100 times the number of turns as the
power winding in order to pe
rmit control of the power winding with low current DC.  If the power and
control windings have the 
same number of turns, then it will require 100 Amps in the control
winding to regulate 100 Amps in 
the power winding.  This is hardly efficient.  With 10 times the number
of turns, control of 100 Am
ps would require only 10 Amps DC and with 100 times the number of turns,
only 1 Amp would be necess
ary.  The winding of several thousand turns on a transformer is daunting
to say the least.  We have
 therefore been looking into the use of transformers with configurations
that would require the lea
st amount of modification.  In the process, we have worked with several
core types: round, EI, figu
re 8, etc.  A recent post to the HV list by Aaron Holmes suggested the
possibility of using two sep
arate transformers.  Having a huge supply of MOT's many of which are
identical in brand and model n
umber, we decided to test this concept.  We are pleased to report a very
successful result.
> >
> >Two pairs of MOT's were selected.  Each MOT was of the older stouter
design type, weighing aroun
d 15 lbs. and possessing heavy gauge primary windings.  For each pair,
the primaries were wired tog
ether in parallel.  The secondaries were placed in series by connecting
the HV tab of each unit and
 connecting a wire to the frame of each by means of a bolt run through
one of the mounting hotels i
n the frame.  These output wires were connected to the HV side of a
125:1 NST to which a DMM was co
nnected to the LV side.  0-145 VAC was introduced into the parallel MOT
primaries while monitoring 
the DMM for voltage.  If no voltage registered, the DMM was moved to the
HV side of the NST and the
 procedure was repeated.  A value of 30 Volts or less indicated a
successful series connection in t
he 'opposing' sense and confirmed that the transformers chosen were
close enough to identical to pr
oceed.  If the first test had indicated significant high voltage output,
one pair of wires in the p
arallel primary connection was swapped and the test repeated to confirm
that the seriesed secondari
es no longer registered significant voltage.
> >
> >Direct measurement of the inductance of the paralleled primaries was
then performed with an amme
ter in series with the input supply circuit set at 35 VAC.  The ammeter
registered about ? Amp, ind
icating a baseline inductive reactance of around 60 Ohms.  The ends of
the seriesed secondary circu
it were the wires attached to the frame of each transformer.  This
series forms the DC control wind
ing. These wires were attached to the rectified output of a small
Variac.  The introduction of 0-82
 VDC into the control caused the reading on the ammeter to increase
smoothly over the range to a fi
nal value of 16.9 Amps.  We did not push this further due to the 20 Amp
limitation of the ammeter, 
but this corresponds to an inductive reactance of slightly over 2 Ohms,
making the test a resoundin
g success.  With cooling, this pair could reasonably be expected to
handle 40 or 50 Amps as ballast
 and the other pair gave a very similar test result.
> >
> >The question then became whether the two pairs could be successfully
paralleled for higher curre
nt handling capability.  To this end, shunt wires were run to connect
two sets of paralleled primar
ies.  Then, the two sets of seriesed secondaries were connected in
parallel with respect to each ot
her.  A brief power test was performed just to insure that no voltage
was induced into the control.
  At this point, the inductance/saturation testing was repeated on the
combination of all 4 MOTS.  
 The testing was also very successful and the results very similar to
those from the tests of the i
ndividual pairs with a couple of exceptions, which are as follows.
First, the baseline reactance w
as reduced to about ? of the value measured on the individual pairs - 30
Ohms instead of 60.  This 
was to be expected pursuant to the law of parallel inductors.  Second
and more surprising, there wa
s only required a total of 28 VDC in the control to reduce this value to
2 Ohms.  It would seem to 
follow that more pairs could be added with a corresponding increase in
current capability and decre
ase in baseline reactance.  The high end reactance drop should not
resent a problem since the usefu
l range of inductive reactance for most of our project work is about 2-8
Ohms.
> >
> >An admittedly poor but serviceable photo of the 4-MOT reactor stack
has been placed here:
> >
> >http://hvgroup.dawntreader.net/srmots.jpg
> >
> >The schematic is here:
> >
> >http://hvgroup.dawntreader.net/4motreactor.jpg
> >
> >
> >
> >We'd love to repeat this experiment with a pair of identical
transformers removed from 5 or 10 k
VA pole pigs, but alas, they are not a plentiful as MOT's around here.  
> >
> >
> >Questions/comments are welcome.
> >
> >
> >Carl Litton
> >Memphis HV Group
> >
> >
> >
> >
> >
> >  
> >
> 
> 
> 
> 
>