A DIRTY war is raging across the globe. Enemy air strikes target our vast networks of power lines, transmission towers and substations. The grid was engineered to withstand the most ferocious lightning strikes, but struggles to resist these unrelenting assaults. For almost a century the network has been shaped by an arsenal of weaponry developed to counter this formidable foe: bird droppings.
The first major assault occurred in California in 1923, along transmission lines strung for 390 kilometres between the Big Creek hydroelectric plant and the power-thirsty city of Los Angeles. Southern California Edison was one of the first companies to upgrade its lines from 150 to 220 kilovolts. As soon as it did so, the network suffered a spate of blackouts. The problem was caused by “flashovers” – bolts of artificial lightning formed as electricity arcs from live power lines to earthed metal supports – tripping circuit breakers and frying parts of the network.
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There had always been one or two unexplained flashovers a month, but between June and August 1923, 31 occurred. This rate of disruption nearly forced the company to abandon high-voltage transmission and could have stymied its adoption worldwide, says Etienne Benson at the University of Pennsylvania, who has studied the crisis of ’23.
What was going on? Strange and desperate theories abounded. Then, by chance, a worker on the Big Creek line noticed an eagle squirt out a long string of liquid excrement as it took off from a transmission tower. When Harold Michener – an engineer who was also an amateur ornithologist – heard about this, he suspected that he had found the culprit. Bird faeces are electrically conductive, and other power companies had already found that, contrary to superstition, being hit by bird droppings isn’t lucky. Build-up of the stuff on power lines and substations had already resulted in power outages.
Proving his theory, however, would be difficult. If airborne strings of eagle excrement were causing the flashovers, the offending material would be vaporised by the current, leaving no evidence. The best way to find out would be to try and deter the birds, and see if that reduced the rate of flashovers.
Early attempts failed. Installing metal guards on one part of the power tower simply prompted the birds to perch elsewhere. But Michener and his colleagues persisted, adding more spikes to the perch-deterrents – along with eight-foot metal pans to catch falling bird droppings before they neared the live wires. It appeared to work. The rate of flashovers fell to tolerable levels. The engineers also added redundancy to the electricity grid, so that when one part failed, the rest could take over – features that other power companies swiftly adopted.
Today we understand a lot more about the relationship between flashovers and strings of bird excrement. The modern power industry calls these “streamers”, says Rick Harness, an outage troubleshooter at engineering firm EDM international in Fort Collins, Colorado. “Like all good pilots, a bird wants to get rid of unnecessary load, so it voids as it takes off,” he says. Golden eagles are among the most prolific, evacuating an extraordinary 2-metre white arc. The stuff doesn’t even have to touch metal to cause a flashover because high-voltage electricity can leap a fair distance through the air. That’s why boosting the voltage in 1923 invited more outages: the spark could bridge a bigger gap to passing streamers.
Engineers may have won the battle of Big Creek, but the war rumbles on. In the 21st century, bird droppings still fry equipment and cause blackouts. Harness is called in when power companies suspect foul play from birds or other animals. Sometimes a large bird will span parallel wires and cause a short-circuit with its wings, leaving behind a charred corpse as evidence. “But when you show up and there’s no dead bird, you have to sleuth it,” he says.
Blackouts can be costly. In one outage he investigated in South Africa, the power went out at a steel mill and molten steel cooled and fused to the rollers. Eventually it had to be cut away. And the fallout from a single incident can be huge. In 2004, one streamer led to outages across an area stretching from New Mexico to Canada, and .
Streamers may be the most dramatic way for bird excrement to take out the power supply, but they’re certainly not the only one. Roosting birds can also generate a slow build-up of dried-out droppings, and a light rain turns the poo into conducting goo. This is a serious problem for substations, which appeal to small birds, says Raji Sundararajan, an engineer at Purdue University in Indiana, who chairs a US national engineering task force charged with finding solutions to bird droppings. “When I saw it for the first time I was amazed,” she says. “The waste was like a little mountain.” In 2013, a heap of pigeon droppings a metre high caused a blackout in Japan. The only option was to wade in and clean it up.
But it’s not always that easy. Even when the stuff coats insulators on transmission lines 50 metres up, shutting off the power may not be acceptable. That’s when helicopter crews are sent in to blast bird droppings off live wires with a pressure-washer. To guard against the inevitable effects of mixing water and electricity, they use highly distilled water, which doesn’t conduct well. But there’s always the risk of a kaboom.
Some companies have tried shooing the birds away, deploying an arsenal of devices, including propane-powered guns, ultrasonic noise makers, chemical repellents, balloons, flashing lights and plastic owls. All of these methods work – for a little while. “They are just not effective in the long term,” says Harness. The birds get used to the disturbance and settle back in, bowels at the ready.
That’s why most power companies take a more defensive approach. Armour is one option, in the form of shields installed above or around the insulators. These can deflect incoming ordnance, but they are expensive. Many companies also put up spikes and other “perch discouragers”, but a perfect solution is elusive: plastic spikes are weakened by UV light, metal ones can injure birds. If a nesting or roosting bird is causing trouble, it might be tempting to pull out the shotgun and end the problem there – but many birds are protected by law.
Harness favours a tactical approach. “If you remove a nest, the bird will probably come back,” he says. “So instead we relocate it.” It works for serial perchers, too. “If you try to keep them completely off the structure, they just shift to the next structure; you’ll be chasing your tail.” So the trick is to tempt the birds away with a nice perch – either elsewhere on the tower, or on a separate pole – where they can excrete in peace.
If we are ever to win the war on faeces, though, perhaps the infrastructure needs redesigning. In 2014, engineers based in Tallinn, Estonia, suggested several options where conductors are held out to the side of a central pole by angled insulators, so the live wire isn’t underneath any perch. These include V-shapes strung between vertical poles, as well as the Christmas-tree-like “fir and double-fir configuration”. The team also sketched out hanging-basket-like designs that put more distance between perch and conductor.
With some similar features, sleek new T-shaped pylons designed in Denmark are being trialled by the UK’s National Grid. “I would not anticipate streamer outages on these lines,” says Harness. All these suggestions are also gentler on the eye than those old steel-lattice eyesores. If bird droppings bless us with a more aesthetically pleasing network than we have today, perhaps this formidable foe is good luck after all.
(Image: Spencer Wilson, Design Pics Inc/Alamy, Getty Images)
This article appeared in print under the headline “Electrical discharge”
