Re: Saturable Reactor Ballast from MOT's

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

You should cut your schematic in half and add some
elipses in between the two pairs.  Really, the
fundamental unit here is a *pair* of MOTs.  The other
schematic to have would be the 240V "pig" version,
which would be a pair of MOTs on each 120V leg, same
control to each pair, neutral wired straight through.

I move that this be named the "MMSR" (for Multi-MOT
Saturable Reactor) ;-))

Regards,
Aaron Holmes, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: Finn Hammer <f-h@xxxx>
>
> 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
>
>
> Tesla list wrote:
>
> >Original poster: "Carl Litton"
> <Carl_Litton@xxxxxxxxxx>
> >
> >In our research into different types of ballast
> >to control current demand on various projects,
> >we found that it is often useful to be able to
> >vary the current independently of the voltage if
> >a single power supply is to be used for multiple
> >projects with different V and I requirements. In
> >the process, 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 core 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 experimental configuration has
> >given such remarkable results that we find it
> >worthy of being reported separately.
> >
> >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 permit 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 Amps
> >would require only 10 Amps DC and with 100 times
> >the number of turns, only 1 Amp would be
> >necessary.  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 least amount of
> >modification.  In the process, we have worked
> >with several core types: round, EI, figure 8,
> >etc.  A recent post to the HV list by Aaron
> >Holmes suggested the possibility of using two
> separate transformers.
> >Having a huge supply of MOT's many of which are
> >identical in brand and model number, 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
> >around 15 lbs. and possessing heavy gauge
> >primary windings.  For each pair, the primaries
> >were wired together 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 in the frame.  These
> >output wires were connected to the HV side of a
> >125:1 NST to which a DMM was connected 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
> >the 'opposing' sense and confirmed that the
> >transformers chosen were close enough to
> >identical to proceed.  If the first test had
> >indicated significant high voltage output, one
> >pair of wires in the parallel primary connection
> >was swapped and the test repeated to confirm
> >that the seriesed secondaries no longer registered
> significant voltage.
> >
> >Direct measurement of the inductance of the
> >paralleled primaries was then performed with an
> >ammeter in series with the input supply circuit
> >set at 35 VAC.  The ammeter registered about ½
> >Amp, indicating a baseline inductive reactance
> >of around 60 Ohms.  The ends of the seriesed
> >secondary circuit were the wires attached to the
> >frame of each transformer.  This series forms
> >the DC control winding. 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 final
> >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 resounding 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
> >current handling capability.  To this end, shunt
> >wires were run to connect two sets of paralleled
> >primaries.  Then, the two sets of seriesed
> >secondaries were connected in parallel with
> >respect to each other.  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
> >individual pairs with a couple of exceptions,
> >which are as follows.  First, the baseline
> >reactance was reduced to about ½ 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 was 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 decrease in baseline
> >reactance.  The high end reactance drop should
> >not resent a problem since the useful 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
> >
> >
> >We'd love to repeat this experiment with a pair
> >of identical transformers removed from 5 or 10
> >kVA pole pigs, but alas, they are not a plentiful
> as MOT's around here.
> >
> >
> >Questions/comments are welcome.
> >
> >
> >Carl Litton
> >Memphis HV Group
> >
> >
> >
>
>
>
>
>