> > I've seen accounts of an extremely  substantial arc being drawn
> > between telephone exchange busbars fed from 50V N,000 Ah lead acid
> > batteries - probably 2000-3000 Ah.
> > In one case technicians had unbolted locating clamps while the busbars
> > were carrying telephone exchange current - probably hundreds of amp,
> > and did not realise that there were strong attractive forces present.
> > Oops. The circuit was eith unfused or the fuses were happy to sustain
> > the arc and it had to be extinguished by 'other means'.
> >
> > In another incident someone shorted between two busbars with a metal
> > vacuum cleaner suction tube. !
>=20
> That would be impressive.

Well, if we're going to start telling "fish stories" about arcs, I'll have
to share mine...

More years ago than I would like to count, I developed the software that ra=
n
the Niagara Falls Robert Moses hydroelectric plant. There were 13 units,
each 167MW, in the main plant. The units generated at 13KV, but the voltage
was immediately stepped up to 115KV by a transformer in a concrete enclosur=
e
with a large hole (for ventilation I suppose) in the concrete roof. A
maintenance worker was up on top of the enclosure and dragged an extension
cord across the roof, and it fell into the hole, directly onto the 115KV
line. I don't know how long an arc was sustained, but I do know the unit wa=
s
offline for month(s?) to repair the damage. The surge on the extension code
took out (vaporized, really) the entire length of the extension code, and
the wiring in the conduit leading to the outlet it was plugged into.
Amazingly, the maintenance worker survived, I believe without any permanent
damage.

-- Bob Ammerman
RAm Systems



--=20
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