🚀 go-pugleaf

In article <3186@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes about
his high-school experience of discharging a large HV oil-filled capacitor.
I too made a mistake in discharging a low inductance cap with a screwdriver.
I had a 16 uF, 4KV discharge capacitor (0.1 uH series inductance) charged to
600 volts when I used a screwdriver to short it.  After all, I had discharged
several hundred microfarads of electrolytics before with only a small spark.
Like Larry found out, the bang made my ears ring for an hour and the flash
blinded me for about 10 minutes.  It burned off 1/4 inch of the screwdriver.
I now have another discharge capacitor: 18 uF, 10 KV, 0.04 uH series.  A quick
calculation says at full charge, this will hold about 300 times the energy as
the 600 volt situation described.  Believe me, this thing is now kept with a
shorting bar permanently affixed across its terminals.  Dielectric absorption,
the bane of audio phreaks, can partially recharge these capacitors even after
they have been momentarily shorted.  While this effect is small in these oil-
filled capacitors, it can still be dangerous.

I don't know exactly what is lethal in terms of stored energy for these
capacitors.  I have recently been working with a HV power supply made by
Glassman High Voltage  (75 KV, 3 mA).  The Glassman engineers told me that
they consider 4 Joules to be fatal (although, of course, many people have
survived far more - but why take chances?).  At the higher voltages, skin
resistance offers virtually no protection at all.

Another thing to worry about with oil-filled HV capacitors is that until only
a few years ago, the filling oil was a polychlorinated biphenyl (PCB).  The
disposal of these capacitors can be a significant problem.  David Anthony
pointed this out to the net once about a problem he had with the capacitors in
an older broadcast transmitter.  The laws governing the transport and disposal
of PCB containing materials are quite strict.

My overall recommendation:  be careful!
                                                    Barry
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|  ___  ________  |
| |  / /        | |  Dr. Barry L. Ornitz  UUCP:..rutgers!rochester!kodak!ornitz
| | / /         | |  Eastman Kodak Company
| |< < K O D A K| |  Eastman Chemicals Division Research Laboratories
| | \ \         | |  P. O. Box 1972
| |__\ \________| |  Kingsport, TN  37662       615/229-4904
|                 |
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