An absolutely beautiful piece of high voltage geek material from itmustbelupe … who has the best taste in these things :).
So what’s going on here is actually pretty awesome. They’re testing a high voltage isolating switch
There is a 500kV long distance power transmission line off to the left. There is a large isolator switch in the middle to disconnect the wonderful little gizmo on the right. The gizmo on the right being a power factor corrector. It looks like, at the time they were doing the test, the transmission line was actually disconnected from load, so all the power factor corrector is doing is dealing with the capacitive effects from the line. Very little current flowing therefore.
If you look carefully at the video, you’ll see an arc skips across one of the horizontal tubes to the right of the switch as it starts to open. These two tubes are actually interrupters, filled with sulphur hexaflouride to quench the arc. They contain a pair of contacts which are moved apart to break the flow of current, drawing the arc as they do, until it’s extinguished by the dense gas filling the tube. There are two tubes on this switch, which operate simultaneously, in order to handle the high voltage.
Unfortunately, on this switch, one of the interrupters has a leak, and all the sulphur hexaflouride has leaked out. Ooops! That means when the contacts move apart, it just arcs internally, the ionised gas forming a near-zero resistance path for the current to flow along. That leaves the second interrupter all alone to break 500kV, which it does, except the distance along the outside, through the air, is too short for that to be effective, and it tracks along the surface instead. Again, ionising the air and forming a near-zero resistance path. You can see the arc extinguished after a short time, as the contacts close again, expecting the isolation to be in place.
Having suffered this complete failure of the interruptor, the isolator itself opens whilst one of the phases is still carrying current, forming this beautiful arc that climbs towards the sky as the heated air rises. Eventually, the line is isolated somewhere further upstream, cutting the display short.
