This video clip was captured by the maintenance foreman at the 500 kV Eldorado Substation near Boulder City, Nevada. It shows a three-phase motorized air disconnect switcher attempting to open high voltage being supplied to a large three phase shunt line reactor.
The arc stretches upward, driven by rising hot gases and writhing from small air currents, until it easily exceeds 100 feet in length. Switching arcs usually terminate long before reaching this size since they normally flash over to an adjacent phase or to ground.
… As impressive as this huge arc may be, the air break switch was really NOT disconnecting a real load. This arc was “only” carrying the relatively low (about 100 amps) magnetizing current associated with the line reactor. The 94 mile long transmission line associated with the above circuit normally carries over 1,000 megawatts (MW) of power between Boulder City, Nevada (from the generators at Hoover Dam) to the Lugo substation near Los Angeles, California. A break under load conditions (~2,000 amps) would have created a MUCH hotter and extremely destructive arc.