Jim
Had a similar wake up call where I work as
a consultant. Come in one morning, one
compartment of a double ended 1000/1250kVA
substation is open and has a fan blowing on it.
Vacuum bottle contactor direct mounted to 1.6kA
bus ( main is OCPD). OL had been tripping
and reset multiple times, without finding
reason and correcting issue causing OL trip.
Called a plant meeting advising plants have
been destroyed and people killed or severely
injuried trying to restart into a fault.
OBTW the cal/cm^2 at 18" was 54 (no safety
PPE exists energized work prohibited). Motor
was "only" 350HP and 480v.
Does someone have a death wish out there?
On Thursday, September 11, 2014, Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:
> 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.
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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