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Registered Member #1159
Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84
My 125 KV X-ray transformer is going back together soon & I'm looking for a way to current limit the primary side. I picked this up off ebay for cheap. It's a solenoid coil from a Cooper power systems oil circuit recloser. This inductor is rated at 100 amps @ 2.4 kv to 14.4 kv. It has an inductance of 60 uh & when I inserted a hollow steel tube, the inductance increased to about 73 uh. I'm thinking this is not enough inductance to current limit this transformer. Would a solid steel rod further increase inductance? I don't have the transformer back in oil yet, so experimenting with this is limited.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
You could probably get the inductance of that coil all the way up to 60mH if you constructed an E I core for it, not with a single rod though. I think your best bet would be to ditch that coil (being rated at 100A it is totally overkill anyway), and make a ballast from an MOT.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
You definitely want something in the low mH range, not uH. The MOT thing works great. I don't know about NY, but in Seattle I can usually find half a dozen MO's in the "free stuff" category on Craig's List. So, if you ignore gas (hard to do, I know), then there's probably a free MO just a mile or two away that could be dissected and made into a fine ballast.
When I first played with pole pigs, my pole pig "test kit" consisted of a little 1500W space heater. Worked great. My first PT and pig-powered coils used the two-500-foot-spools-of-wire ballast. Now I've got a 120V 45A Luxtrol variac. Unmodified, it passes about 20A with 2/3 of the windings engaged. Perfect for PTs and other smallish non-shunted transformers. In case you haven't got a variac and were looking for an excuse to get one...
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Current limiting ballast for X-Ray transformer
