Back in December, a Wyoming rancher described to me the terrifying fireworks that ensue when a bolt of lightning hits a wind turbine.
“It will explode those blades, and they’ll throw chunks of blade several hundred feet,” said Ralph Brokaw, whose ranch accommodates both turbines and cows.
After I wrote the post, I got an e-mail message from Kim Loehr of the Lightning Protection Institute. She wrote to tell me that the National Fire Protection Association has updated its handbook on installing lightning protection systems to include a new section on wind machines.
Due to the proliferation of wind farms and the increasing heights of the turbines – some of them more than 250 feet tall – there is, she noted, a rising number of lightning-related incidents.
Now that the thunderstorm season is rolling around (central Texans were roiled by lightning shows over the weekend), I thought I would share a few pointers.
According to the handbook, wind turbines are particularly complicated to protect because they have so many different components – including non-conducting composite materials like glass-reinforced plastic. Any lightning protection system must therefore be sufficiently comprehensive to take account for all of the parts.
“While physical blade damage is the most expensive and disruptive damage caused by lightning,” the handbook states, “by far the most common is damage to the control system.”
The massive blades will often have a receptor at the tip, which can channel the lightning into the proper wires and onward to the ground. Two receptors might be necessary for larger blades.
“Protecting wind turbine blades against lightning is not about avoiding strikes, but attracting them,” states LM Glasfiber, a global blade manufacturer, on a section of its Web site devoted to lightning. “This makes it possible to direct the flow of the lightning and ensure that the components exposed to its effects can withstand the forces involved.”
The company says that it meets certification standards requiring blades to be capable of withstanding 98 percent of lightning strikes.
Without the system, though, it’s not pretty: “A lightning strike on an unprotected blade can lead to temperature increases of up to 30,000 degrees Celsius, and result in an explosive expansion of the air within the blade,” LM Glasfiber states.
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