California Wildfires / Utility Power Lines

[saladhawks]

Several of the recent wildfires in California were caused by arcing from utility power lines. I have heard that Southern California Edison power lines caused the Malibu fire, while San Diego Gas and Electric power lines caused the big fire in North San Diego (lawsuits have already been filed by certain homeowners).

I have not been able to determine the exact cause (i.e. downed primary conductor, downed secondary conductor, tree branch in overhead conductors, etc.), but it does sound like it involved distribution class infrastructure in each case.

I was wondering if it is time to approach these events with some new ideas. Such as:

(1) Requiring primary tree wire for all distribution class infrastructures in "high risk" areas. Even go so far as to require 100% primary insulation in such "high risk" areas.

(2) Revised protective relaying schemes to detect downed primary distribution conductors.

(3) Require utilities to protect secondary conductors in "high risk" areas, as the service drop from an Overhead transformer to a customer service panel is not currently protected.

Any other thoughts????

 

[jghrist]

Of course, the first order of business would be to determine what lines caused the fires.

Primary tree wire costs a lot more than bare. If the fires were caused by intact wires touching trees, then tree wire may help. If it is because of downed lines, then it may hurt. Insulated wire burns down easier than bare wire because an arc is prevented from travelling along the conductor and the heat is concentrated on one spot.

Detecting downed conductors would be a good idea if this caused the fires. Several new relays proportedly can do this. It remains to be seen how successfully. Besides the cost, there is the question of reliability.

Secondary and service drops are mostly insulated. If they break and fall on dry brush or grass, they could cause a fire, I guess, by arcing from the cut end. Tripping for a high impedance fault on a service would be much more of a problem than for primary conductors, however. Putting a $4000 relay on each transformer would increase costs a bit.

 

[davidbeach]

The downed wire detection algorithms are all SLOW. None of them would do any good at preventing a downed wire from causing a fire; it is the arcing that is used to detect the downed wire and by then the fire would be roaring along.

 

[waross]

There was an instance about 15 or so years ago in North Vancouver, Canada.
It was one of the hotter days of the year. The heavy AC load on a 500KV transmission line coupled with the hot weather resulted in heat induced expansion of the conductors and greater than normal sags. One of the conductors flashed to ground where the line crossed a small ridge and started a bush fire. While the fire crews were extinguishing the fire, the line flashed again. I believe that a fire fighter was fatally injured by the second flash.
The cause of the flash-overs was not publicized. Possibly lightning strikes some distance away, but I don't know for sure.
respectfully