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Dan,
Saturable reactors are unusual beasts. If you look at a photo of an un
potted, un-enclosed one, you will see that there are three windings
which surround two separate cores.
If you look carefully, you will see that there is one outer winding
layer that goes through both cores. This it the control winding.
Closer to the cores, there are two separate anti-series connected
windings, each of which go only around one core. These carry the
current that is to be controlled.
A steady DC current through the control winding establishes a fixed
magnetic field in both of the cores.
When there is no DC control current, the cores exhibit their maximum
permeability, and therefore, a high reactance, like a welder with the
output leads disconnected (not shorted). Two cores are used, wired in
anti-series, so that the sum of the net voltages induced in the control
winding works out as close to zero as possible.
As increasing amounts of DC current are injected into the control
winding, the cores get closer to saturation, allowing increasing amounts
of current to flow through the power circuit. This would be analogous
to inserting progressively smaller resistances between the welding
electrodes, until the maximum rated amount of control DC is achieved,
and you have essentially no resistance in the welding electrode circuit
-- you have simply shorted the leads.
A saturable reactor gets you to the same place as a shorted welder, but
allow readily variable control of the current, instead of an all-or-none
option.
All of the saturable reactors I have ever seen to not do any voltage
transformation, only current limitation. I suppose it might be possible
to construct a combined HV transformer and saturable reactor, but the
cost would be prohibitive unless you were planning to buy 10,000 of them.
You can make your own saturable reactors if you have an ample supply of
matched microwave oven transformers. The transformers have to be
matched, or you will induce unwanted voltages in the control windings.
You drive out the magnetic shunts from each unit, and connect the
original primary windings in series. The connections would be like
circuit arrangement "B" in the reference above.
The original HV windings become the control windings and are connected
in anti-series. The primaries have to be phased correctly so that the
AC output from the HV windings is in the opposite phase and cancels out.
You then apply your DC control voltage to the former HV windings. As
the applied DC current increases, the amount of current permitted
through the primaries will increase as well. Probably not big enough to
power a pole pig, but enough to experiment with for a small TC.
Dave
On 6/6/2018 11:13 AM, Daniel Kunkel wrote:
Dave,
Wow those commercial saturable reactors are beasts! I wonder if it would be
possible to build in current limiting into the pole pig itself (much like
an NST)? You could you add shims into the cores of the pig itself (of
course you loose real time adjustments on a running system). Or perhaps by
removing the pig's core and transplanting into a different case that had an
adjustment knob/wheel/lever to raise and lower the core would be better.
~Dan