On 07/07/2013 19:15, Andrew Mawson wrote:
wrote in message
...


You see a lot of 3 wire transmission lines across the countryside. The
lines are spaced about a meter apart and are supported by relatively
close-to-the-ground wooden poles which aren't dissimilar to telegraph
poles in appearance. You could reach them with a fishing rod they're
that low in some places. I saw some hapless tree surgeon lop off a
branch once that landed across two of these wires. Two little fires
ignited at the contact points. Didn't look anything special at first.
I expected an upstream breaker somewhere to activate and shut off the
current, but that didn't happen. The fires grew rapidly and within one
minute at the most there was the most *enormous* flash and ***BANG***
and everything then fell earily silent. It was one of the most
spectacular things I've ever witnessed. Turned out the power to a
couple of hundred thousand homes had been lost as a result. Would this
have been one of your 33,000V lines? The homes affected were as far
away as 35 miles from the incident, btw.

Almost certainly 11kV on lines as you describe

AWEM

Agreed, and certainly not serving 200,000 homes unless it caused a trip
in one of the much higher voltage lines, which I would have thought was
unlikely.

It went quiet because a breaker did operate, but only once there was
enough ionisation from the fire to allow an arc between phases or from
phase to ground. Perhaps a few hundred amps? Which is a few megawatts,
maybe 1000 homes?