by Nick Gromicko, CMI®
Wind turbines are tall, isolated towers composed of sensitive electronics, all of which are factors that make lightning a persistent and real threat. A properly installed lightning protection system, however, will intercept the lightning and effectively and safely conduct it to the earth without risking physical destruction to the wind turbine. This issue has become increasingly critical as wind turbine systems become more sophisticated and vulnerable to lightning. Lightning protection systems costs less than 1% of the total capital expenses while improving the cost-effectiveness and reliability of a wind turbine substantially.
First, a few facts to convey the danger that lightning poses to these power-producing windmills:
- According to a German study, lightning strikes accounted for 80% of wind turbine insurance claims.
- During its first full year of operation, 85% of the down time experienced by one southwestern commercial wind farm was lightning-related. Total lightning-related damage exceeded $250,000.
- The German electric power company Energieerzeugungswerke Helgoland GmbH shut down and dismantled their Helgoland Island wind power plant after being denied insurance against further lightning losses. They had been in operation three years and suffered more than $540,000 (USD) in lightning-related damage.
Wind Turbine Component Damage
The following systems, arranged in order from most to least vulnerable, may be damaged by lightning
- damage to the control system. These include sensors, actuators, and the motors for steering the equipment into the wind. According to the updated National Fire Protection Association handbook: “While physical blade damage is the most expensive and disruptive damage caused by lightning, by far the most common is damage to the control system”;
- damage to electronics. Wind turbines are deceptively complex, housing a transformer station, frequency converter, switchgear elements, and other expensive, sensitive equipment in a relatively small space;
- blade damage. A lightning strike to an unprotected blade will raise its temperature tremendously, perhaps as high as 54,000° F (30,000° C), and result in an explosive expansion of the air within the blade. This expansion can cause delamination, damage to the blade surface, melted glue, and cracking on the leading and trailing edges. Much of the damage may go undetected while significantly shortening the blade’s service life. One study found that wood epoxy blades are more lightning-resistant than GRP/glass epoxy blades;
- damage to generators; and
- batteries can be destroyed, or even detonated, by a lightning strike.
Note that lightning dangers increase with turbine height.
The National Lightning Safety Institute finds that lightning codes, in reference to the danger lightning poses to wind turbines, “provide more benefit to commercial vendors than to those seeking relief from lightning's effects” and that “devices that claim to offer absolute protection abound in the marketplace, confusing specifying architects, engineers, and facility managers.”
An article published in Solar Age Magazine offers the following recommendations for wind turbine lightning protection and inspection:
- Every wire that enters the electrical panel box should have a surge suppressor grounded to an existing ground rod. The installation should have only one ground rod, which should make “better contact with the moisture in the ground than do the tower footings.”
- Lightning rods are not likely to protect the windmill’s electronic equipment. Furthermore, lightning rods may obstruct the flow of wind around the turbine’s blades, reducing the system’s efficiency. This advice contrasts with that offered by Machine Design Magazine, which states that “Franklin-type lightning rods protect [wind turbines] against direct lightning strikes.”
In summary, wind turbines are extremely vulnerable to lightning, but the danger can be mitigated by lightning protection systems.