October 15, 2006 10:14pm
Article from: AAP

WORRIED Sydney householders inundated the fire service with emergency calls after a change in the weather caused power lines across the city to start sparking.

NSW Fire Brigades started receiving the calls about 5.30pm (AEST) today when the prolonged spell of dry weather gave way to light rainfall.

At one point this evening firefighters were dealing with a backlog of 50 calls from all over Sydney about electricity cables that were violently sparking and "scaring people to death", a spokesman said.

The effect – known as arcing – occurs when built-up dust and ash on power lines comes into contact with misty rain.

There is a bright flash, sometimes accompanied by a loud bang – but it is nothing to worry about, according to experts.

"There's nothing you can do about it. It's a matter either of the rain washing the dirt off or it burning off," the spokesman said. "Electricity and water don't mix – that's what it's about."

EnergyAustralia spokesman Anthony O'Brien said there had been no reports of major interruptions to the city's power supply.

"If you are sitting in your home, it (arcing) can sound quite alarming. But it is just like a circuit breaker going on and off," he said.
http://www.news.com.au/story/0,23599,20587302-1702,00.html

This reminds me of only a couple of years ago with the last lot of bushfires. Apparently some of the fires were underneath some of the main feeders for Sydney (132kV and the like) and the flames were high enough to reach the aerial conductors. Every so often at the peak of the fires in the afternoon, there was a momentary glitch in the supply for a few milliseconds.
The fact that flames are conductive doesn't seem to be well known these days, but the properties were known and used in the late 19th century for things such as experimental radio frequency detectors and microphones.

Flames are conductive Aussie ? That is interesting. How conductive are they compared to say; water. Are there any stats or test results around ? I suppose its difficult to get funding for that kind of research.

If flame is fairly conductive then that should have a bearing on HV substation design shouldn't it ? Or does it already ?

Hi kiwi,

Orange and yellow flames are certainly conductive and especially the smoke which is unburned fuel and mostly carbon.

Carbon is a good conductor and can trigger flasovers between phases or across insulators and possibly crack skirts off them.
Also a sustained arc may melt the actual conductor and break the areal conductor.
( like the old carbon rod lamps used in the old movieprojectors ).

If a flame is blue or even invisible, the fuel, air ratio is very good and complete burning is achieved with hardly any waste hence no colour in the flames.

The other factor to bear in mind when bush fires burn underneath transmission lines is the risk of sagging of the lines because of the heat from the fire.