Sparks

This is 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 line reactor is the huge gray transformer-like object behind the truck at the far right at the end of the clip. Line reactors are large iron core coils (inductors) which are used to counteract the effects of line capacitance on long Extra High Voltage (EHV) transmission lines. Internally, this line reactor has three coils, one for each phase in the three-phase system. Each coil within the reactor can provide 33.3 Million Volt Amperes of compensating inductive reactance (MVAR) at 290 kV between each phase to ground . The power company had previously encountered difficulty interrupting one of the three phases when trying to disconnect the line reactor. The substation maintenance crew set up a special test so that they could videotape the switching event, and they also made arrangements to "kill" the experiment, if necessary, by manually tripping upstream circuit breakers.

I don't understand everything in the above paragraph, but let me summarize the highlights:

• 500,000 Volts

I've heard that some places will keep a tank of compressed air on hand and use it to shoot a blast of air at the arc when they open the switch to "blow it out".

Update February 2018 replaced missing video.