Content-Transfer-Encoding: base64Dan,
A shorted welding transformer stores energy in
an expanding magnetic field which is then
returned to the power circuit as the sine wave
of the input power waveform decays, kinda like
compressing a spring. When you relieve the
pressure on the spring, the spring pushes the energy back into your system.
If you use a resistor, the resistor converts the
energy to heat, which is lost, and not returned
to the system. This is much less efficient. It
would provide ballasting, at the expense of a
lot of waste heat. Any resistance in the
ballast components will generate waste heat, so
you want to minimize that as much as possible.
If you want an easily and infinitely adjustable
ballast, you would use a saturable
reactor. This is a special transformer which
would perform the same function as a shorted
welder, but in which the permitted current is
controllable by a small low voltage DC current
applied to a special set of control windings.
Saturable reactors provide nice control for TC
systems, but ones big enough to effectively
control a pole pig can easily weigh half a ton,
and are usually very expensive, unless you can find a surplus unit for cheap.
Last spring, I bought an assembly nearly
identical to the following one for $130 for the
copper scrap value, but it cost me $580 in
shipping fees to get it to my friend's factory
shipping dock. "Some day" I hope to build a coil
big enough to put it to effective use.
https://www.ebay.com/itm/40-KVA-20-AMP-460-VOLT-HUNTERDON-SATURABLE-CORE-REACTOR-TRANSFORMER-S-1207-1/292572873068
The reactor that was in it looks just like the
following one, but is mine "only" 52 KVA
rated. I think there is a typo in the
listing. The rating should be more like 60 KVA,
not 600. I would speculate that a 600 KVA core
would likely weigh several tons.
https://www.ebay.com/itm/NEW-Hunterdon-Saturable-Core-Reactor-Transformer-600KVA-60Hz-WE-1097-R-C98R2/282780054079
(I have no connection to either seller.)
You can buy a lot of welders to short out for $4,800 plus shipping.
To understand saturable reactors, look up "magnetic amplifiers" in Wikipedia.
Dave
On 6/5/2018 11:22 AM, Daniel Kunkel wrote:
As already pointed out, for a current limiting ballast transformer, the
secondary coil will be shorted out, and the primary will be in series with
HØY??£â?÷vWfW"Â??fR&VVâvöæFW ing what would happen if you put a (variable)
resistor on the secondary side of the ballast transformer (instead of a
dead short). I wonder if this would give you some degree of variable
Ý\??[?[Z][?Âg&öÒÆÂ×?&VF?ng, it seems like the best current
[Z][?È\Ù\È?Õ@nductance and resistance...so I wonder if resistance
Àcated in this location would work.
?[???×××××××××××××À_________________________________
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