On Jan 27, 2:44*pm, Jules Richardson
wrote:
On Fri, 27 Jan 2012 09:56:12 -0800, DerbyDad03 wrote:
*We
grabbed another dead man stick and still got quite a bang out the cap
since it didn't completely discharge before blowing up the other dead
man stick.

Effect of dielectric absorption, possibly? You short it briefly, it
discharges, but then a small portion of the original charge level appears
to come back moments later...

(http://en.wikipedia.org/wiki/Dielectric_absorption)

cheers

Jules

I am familiar with that phenomenon, although in this situation, I'm
pretty sure it was the result of a partial discharge before the
grounding rod exploded. Obviously I can't proof it, that's just my
guess, based on prior experience with these large caps.

As part of our bi-weekly transmitter maintenance, we would ground the
caps prior to removing the bus bars to get them out of the stand-by
transmitter. Before they were even lifted out of the transmitter, we
always put a shorting cable on them to stop them from charging back up
due to both dielectric absorption and the strength of the signal from
the on-air transmitter.

On the rare occasions that we forgot to do this (newbies!) or noticed
a bad ground connection, we would use a dead man stick to short them
before grabbing them. Even after a few hours, the discharge was
minimal and we might get a little bit of a pop. In the case of the
training demo, which was done in a rather neutral environment (the
mess hall, a 1/4 mile from the transmitter building and tower) the
resulting discharge was quire substantial, much higher than anything
we'd seen in "real life".