I dropped out of college for a couple of years (ran out of money)
and went to work at a capacitor factory (which will remain unnamed
to protect the guilty) as a Quality Control Tech on the production
The owner of the place was a MSEE, and the company specialized in VERY high voltage capacitors, and high voltage power supplies. We made a VERY good product, but the production line testing techniques were, to say the least, hair raising; I saw more than one tech quit after one day on the job.
Typical hipot test, on an 8 MFD, 5 KV capacitor; put it on a table with a grounded metal top. The tech grabs a pair of home built test prods, connected to a high voltage supply with a variac on it, and applies the prods to the cap terminals.
Specs called for charging the cap to 10 KV and holding it there for 1 minute.
If the cap doesn't fail, so far so good. If it fails, it does it in one of a couple of modes.
The GOOD failure mode; there is a sharp metallic click inside of the can as the sections arc inside of the oil and discharge.
The BAD failure mode; the solder seals blow and oil sprays all over the place!
What made it interesting every day... before starting work, we checked a wet bulb / dry bulb thermometer and using it's readings computed the humidity. If it was over 75%, we spent the day working on small, low voltage stuff. If you tried to charge anything big, sure as hell it would flash over to ground with a sound like a 12 gauge shotgun going off in your face!
Most of the line techs were habitually on sedatives and antacids because of the fear factor... and the Old Man in the corner office insisted that 10 KV was TOTALLY safe, and we had NOTHING to worry about!
Anyway... you now have a 5 KV cap sitting there charged to 10 KV. What do you do with it NOW?
VERY simple, Grasshopper.... there is a THIRD home made test probe.
This one is tied to a bank of resistors mounted on a sheet of plywood. You use it to discharge this nasty little beastie.
Not all that simple, really... it's an art that it took a couple of weeks to learn.
You approach the cap like you'd approach a cobra that you're trying to milk for venom. SLOWLY... CAREFULLY... you move in with the resistor probe. You DON'T move in too fast, or you get another chorus of the 12 gauge Remington Pump Sonata in your face as it ALL lets go at once, flashing over the resistor bank.
If you've done it RIGHT... about 6 inches from the terminal there is a beautiful purple streamer to the end of your probe, and a faint hiss as the juice goes to ground thru the resistor bank.
Once you have the dragon stuffed back in his cage, the FIRST thing you do is grab one of the MANY spools of uninsulated wire lying everywhere and your diagonal cutters, and slap a shorting wire across the monster... like RIGHT NOW!
Hairy procedure all around.
One day a new directive came around. There was a bottleneck in the plant on larger capacitors; they were piling up waiting for hipot testing. We had only ONE high voltage testing cage (it took caps up to 100 KV working!), so to increase production flow the Old Man in the Corner Office decreed that open air testing like I just described would now be done on caps up to 15 KVDC working... which meant using hand probes about a yard long to charge to 30 KV!
Two guys muttered obscenities along with the words "I Quit!" and stalked out the door. The rest of us said "No Way, Jose", and told the owner so in no uncertain terms!
He came around and told us we were all cowards, and told us something we hadn't known about him (and which explained a lot really)... he'd gotten the money to start his company in London at the end of WW2; he'd stayed after the war & worked at DEFUSING UNEXPLODED BOMBS for a living!
HE decided he'd show us how to do it, and he wanted no more bitching from the production line!
The old boy grabbed the probes and a 2 MFD, 15 KV cap and had at it himself. EVERYBODY backed up a few yards to watch as he hoisted this ten pound beast onto the table top.
You never saw such an exhibition of arcing and sparking in your life! Repeated shotgun blasts as that cap arced to probes, across insulators, and even to the steel beams that held up the building! Yard long test probes proved to be a good bit more awkward to handle than he'd thought they were.
He FINALLY got it to 30 KV... and then went in with the resistor bank probe.
Sometimes you just live right, or at least lucky. Before he got the probe to it the cap failed... in the BAD mode!
There was a muffled WHOOMP! and the entire top, six inch insulator and all, went flying into the air as the solder seals blew out! That was followed by a flying spray of mineral oil, and a billion bits of paper and aluminum foil as the capacitor sections shredded themselves. It was like a cherry bomb went off inside of that capacitor... absolutely BEAUTIFUL, and the Old Man was COVERED with the flying debris as most of us dove for cover!
Gathering up as much of his tattered dignity as he could he wiped off his oily glasses, put them back on, and a badly shaken MSEE walked away without a single word.
Within the hour a new directive came out returning us to the old open air testing limit of 5 KV caps.
Sometimes all it takes to restore sanity is for theory to meet reality head on...
Mr. T., W9LBB