D
Don Kelly
- Jan 1, 1970
- 0
-------------daestrom said: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.
High voltage air blast breakers for AC have been around since the late 40's.
They were/are modular with series sections and could then be extended to
higher voltage by adding sections. The contact opening in a section was
about 1 inch and 600psi air was driven through the arc, extending it towards
a vent but not actually interrupting the arc until the arc naturally
collapsed at current zero- then the arc products were blown out and the gap
filled with good dielectric (high pressure air). A two gap section was good
for 72KV and 2 of these in series for 161KV. Two gap sections could be
linked together and put on longer columns at higher voltages there was a
loud bang when they operated. The advantage of these breakers from Europe
was that they were smaller, lighter, faster and cheaper than the oil
breakers in use up to that time in North America.
There was a bit of a war of words going on in IEEE PAS regarding the
relative merits of bulk oil breakers and air blast breakers and air
breakers won out. Even the old circuit breakers at, say 15KV up whether
oil or air blast operated on the principle of removing arc products,
replacing them with good dielectric, when the current went through zero.
This principle is used for HV minimum oil and SF6 breakers (blast of oil or
SF6 through the gap).
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.
------------
At lower AC voltages- say 5-15KV such breakers are often used- You could
take one of these and derate it to about 400-500VDC and it would likely
work. That current zero every half cycle makes a big difference.
But I've seen enough stuff that I know I haven't seen everything
daestrom
Me too