New: A Solution to Powerline-Sparked Wildfires: Over-Grounding

Gar Smith
Monday October 30, 2017 - 12:14:00 PM
Gar Smith

There is concern that PG&E's electric transmission lines may have played a role in Northern California's devastating wildfires. Many times in the past, falling branches and trees toppled by high winds have crashed into electric transmission lines triggering grassfires that have erupted into major blazes. (It's happened before: in 2015, a damaged PG&E powerline started a fire in Amador County that fire burned for 22 days, killed two people, destroyed 549 homes and blackened 70,868 acres.)

During October's winds, cellphone images captured transformers dramatically erupting along suburban streets, underscoring the ignition potential of powerpoles inside cities as well as in the wooded foothills surrounding them.

The obvious solution—practiced in most of the world's developed nations—is to relocate these risky overhanging electric lines by placing them underground.


For anyone who travels abroad (to countries where powerlines are secured underground and out-of-sight), it can be an embarrassment to return to the US and having to face the visual anachronism of our national power grid—still largely supported by millions of pine, cedar, and fir trees conscripted from our forests and turned into load-bearing wooden polls treated with toxic preservatives like creosote and pentachlorophenol. 

PG&E has considered the option of "undergrounding" its rural grid but has moved slowly citing the high costs of this alternative. While San Diego Gas & Electric has place 60 percent of its grid underground, PG&E has only managed to underground 30 miles a year. 

Undergrounding power lines can cost four to 14 times as much as hanging overhead wires. One reason is that the trenches need to be 10 feet deep and five feet wide. Underground lines are also more vulnerable to ground movements including earthquakes. 

Burying cables presents an added inconvenience when it comes to maintenance. Servicing buried powerlines is more time-consuming and expensive than responding to interruptions in a grid that is accessible without having to use backhoes and shovels. 

But there is another option to consider. 

The Affordable 'Half-way" Solution 

There is an alternative that avoids the risks of hanging wires and the cost of buriing cables underground. You could call it "Overgrounding." 

With this approach, powerlines are secured inside long lengths of metal or plastic piping held firmly in place by small, inexpensive-but-sturdy concrete pylons. 

Placed a few feet the surface of the land, these electric "pipelines" would not disrupt movements of wildlife or flowing water. At the same time, they would remain readily accessible to utility crews who could service the system on foot. There would no longer be a need to truck in vehicles with elaborate "cherry pickers" to raise workers 30 feet in the air to gain access to overhead power lines. 

More importantly, "overgrounding" would eliminate the risk that falling branches or toppling trees could snap exposed electric lines. 

While "overgrounding" would not be appropriate for urban settings, it should be ideal for rural locations. The pylons and pipelines could be quickly installed over existing transmission routes. Existing powerpoles are installed about 160 feet apart. On those occasions where the old overhead lines cross roads, rivers, or ravines, a simple "bridge" structure could briefly elevate the protected powerlines. 

One concern that arises is: "What about the threat of vandalism?" Simple answer: overgrounded power lines would be less susceptible to vandalism or "terrorist" attacks than existing overhead lines, held in place by wooden poles that could be chain-sawed or torched. (Such attacks do happen, but rarely). As a further deterrence, the Idaho National Laboratory has devised "inexpensive, easy to install, and minimal maintenance" surveillance devices that can detect and communicate signs of tampering in real-time. Powered by the transmission line itself and able to operate on their own stored power in the event of a line failure, these small monitors are so sensitive they can detect "the hand removal of a tower base support nut." 

Here is an artist's rendering of what a cheap, convenient, "overgrounding" system might look like.