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Chris,
I have asked the same question, without a satisfactory answer.
A couple of years ago, I had to replace exotic unobtanium
current-limited ex-mil-spec-radar power transformers on a vintage TC
that was originally built by Harry Goldman. The replacement transformer
that I hadfor the setup was a 9 KV monster plate transformer from
Hammond Engineering, rated for something near 500 mA full tilt, and most
definitely NOT current limited.
I used a beefy saturable reactor to control the current, and I think the
coil performed even better with this arrangement than it had with its
original transformers. The one odd thing that I noticed was that it took
about half a second for the TC discharge to stop after I shut off the
power to the reactor control windings. The TC discharge definitely
decayed perceptibly over something less than a second. There was no
capacitance in the control circuit. Not a fatal problem, but a definite
curiosity.
Last May, I scored a 55 KVA water cooled saturable reactor for the
princely sum of $130.00 (plus $550 for LTL freight shipping to my
friend's factory dock). As a bonus, it came in a 400# steel cabinet
with massive control relays, the DC power supply for the reactor, and a
1,000# low voltage, high current transformer rated for 12/15/17.5 volts
at 1,500 amps. The transformer has secondary windings that are 0.5" x
1" hollow copper water cooled rectangular bars. If I ever get my
4CW100,000 VTTC built, it will be the filament transformer.
The following assembly is nearly identical to what I purchased, but my
system was rated higher, and didn't have quite as many smaller
electronic components inside. It certainly came from the same manufacturer:
I only found my reactor after a multi-year standing search, and watched
that particular item as its price dropped incrementally from $2,995 down
to $130 over at least 18 months. I would speculate that few reactors
are used in amateur TC work because they are uncommon in the first
place, and usually pretty expensive when compared to the more common
technique of using a pair of 200 amp Lincoln stick welders with shorted
outputs, obtained used from the want ads or Craigslist.
Interestingly, on my reactor, and on a couple of the ones pictured on
eBay, there is a 30 watt wirewound resistor connected directly across
the control winding terminals. The resistor is thoroughly cooked on my
reactor, and I can't see a rating on it. I can't fathom what its
purpose was.
Dave
On 2/15/2018 11:18 AM, Chris Boden wrote:
Why is it that Saturable Reactors are so rarely used in HV Hobbyist
applications such as Tesla Coils?
We've been using Variacs for generations, we're great at Voltage control.
But when it comes to current limiting the hobby world tends to fall short
and go with some incredibly crude solutions.
Saturable Reactors seem to be the MiniDisc of the HV world. They work,
they're an elegant solution, but they're hard to find and weird so nobody
ever uses them.
Thoughts? Opinions? Wild conjecture?
I'm genuinely curious and hoping someone has some ideas on this.