Jules wrote:
On Wed, 14 Oct 2009 17:30:15 -0400, daestrom wrote:

Jules wrote:
On Tue, 13 Oct 2009 19:51:24 -0700, Don Kelly wrote:
Other
hazards such as arcing at switches or poor contacts, worse with DC, were
ignored.
I recall the breakers at one site I was working at fed compressed air
through the breaker upon opening, just to extinguish any arc that may have
formed (that was a 400V DC setup) - I think that's typical on higher power
DC stuff. The breakers were about the size of a lunchbox.

Hi voltage AC breakers still do use compressed air in some. The 'blast'
is aimed between the arcing contacts to literally blow out the arc.

Lower voltage DC (up to 350VDC) that we used on submarines just used
blow-out coils to create a magnetic field that 'pushed' the
arc-conducting gases up into chutes lined with alternating metal and
insulating plates that would cool and stretch the arc.

Interesting - not seen those before. 'ours' were WWII-vintage, and there
was compressed air in the same room as part of the air-start system for
the generators, so I suppose it was no big deal to route it to the
electrical switchboard too.

But I've seen enough stuff that I know I haven't seen everything :-)

:-) I'm sure there were all sorts of ways and means of extinguishing
arcs, though - some of which may have worked better than others!

It'd be interesting to know what larger power stations etc. did, too. Had
some friends in NZ with a smaller plant (2,500 kVA) but I've not talked to
them in quite a while, and I don't recall anything obviously resembling
breakers on the site, although I assume they were there somewhere!


Another variant that I worked with was spring to open and the bottom
side of the mechanism pushed a plunger in a cylinder to make a 'gush' of
air that was directed from below the contacts, up between them into the
arc chute. Of course it was just a short burst of air, but the idea was
to blow the hot gases up into the chute where the plates would
separate and cool them.

daestrom