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Jason's recent post
"A coworker and I once used a solid state relay to control the charging
transformer on a 1 kJ cap bank. While debugging the trigger system
(ignition coil plus light dimmer trick), EMI from the trigger
transformer was turning the stupid solid state relay on (this was a 3-32
VDC control 30A brick type SSR). This managed to charge the cap up to
lethal voltage without us knowing it (there is a shorting relay in the
permanent setup,but this was a lashup). When I poked the cap terminals
with a multimeter there was a loud bang and a dead meter. I was
incredibly lucky that it was the multimeter that was dead and not me!
We figured out what was happening and immediately replaced the SSR with
an old style contactor. Problem solved."
Note two things, which run through pretty much every exciting moment
I've had, as well.
lashup.. I'll bet more incidents in all sorts of situations have
occurred during temporary tests than during regular operation
(Chernobyl, TMI, etc.)
without us knowing it.. No independent check on voltage. Silent but
deadly isn't good with HV gear.
There's no substitute for clearly visible air gaps or shorting hooks.
That's why you leave the grounding hook on the HV, so it's connected to
ground, while you fool with the circuitry. Sure, the stick will
discharge the capacitor, but if you don't leave it hooked up, it might
become hot again.
BTW, even mechanical contactors do stick closed. And shorting relays
fail to operate.