HIGH MAINTENANCE

International crew’s high-wire act repairs lightning-damaged wind turbine blades

2009-09-13T00:30:00Z International crew’s high-wire act repairs lightning-damaged wind turbine bladesStory By TOM LUTEY Of The Gazette Staff The Billings Gazette
September 13, 2009 12:30 am  • 

JUDITH GAP - The winds that spin the blade tips at 217 mph at Invenergy's 90-turbine wind park also deliver lightning, which can shatter a windmill's 122-foot arms like a truck ramming a fence post.

A blade's outer edge, at the height of its rotation, is nearly 400 feet above ground, an easy bull's-eye for sizzling, fluorescent-blue darts traveling at 130,000 mph and packing a 54,000-degree punch.

When blades are damaged, Julio Moya and a special crew of technicians are summoned to scale the 260-foot towers at Judith Gap and make repairs.

They toil from a bare metal platform suspended 150 feet off the ground by cables strung from the windmill's head. One man stills the blade, which quivers in the breeze like the 6ƒ-ton fin of a wounded whale. Another man applies a poultice of epoxy and fiberglass. Two others, working on the ground, clutch a tether affixed to the platform overhead. They lean backward to counter the 20 mph winds that can bounce the dangling platform like a drunken puppeteer.

Moya stands 50 yards from the tower and supervises from the ground. He is the babel fish that keeps his multilingual crew communicating. He speaks Portuguese to communicate with blade technician Edimar Perida of Brazil, Spanish to talk with Jose Moreno of Mexico, and English for John Tristan and John Aguirre, who like Moya are Texans.

"I might have to learn Japanese," said Moya, with his neck craned upward as he watched Perida and Aguirre. His employer, WindCom, repairs windmills worldwide. Its crews are international.

Blade repairs are tricky, Moya said, because the weight and thickness of the repair materials have to be perfectly matched to the blade. Otherwise, a blade ends up lighter or heavier than the others on the windmill, causing the entire apparatus to wobble like an unbalanced tire and ultimately fall apart.

"We send images of the damage to our engineers in Houston. They send detailed blueprints back about what needs to be replaced," Moya said. "We use different types of fiberglass, different types of composites, determined by where the damage is on the blade."

Blade technicians make $70,000 to $80,000 a year. When conditions are too hazardous to go up in the platform for repairs, they're paid to wait. That's still less expensive than the $1.5 million cost of a new blade, said John Bacon, Invenergy operations manager at Judith Gap.

Windmill blades are designed to take some lightning, Bacon said. There's a tea-saucer-sized copper plate near the tip of each one. By design, the plate is supposed to take the lightning hit and deliver the current to an aluminum ribbon suspended inside the blade and running its length. The ribbon connects to a circuit breaker that grounds the current and shuts down the windmill to prevent any damage.

A lightning strike normally doesn't harm the blade, Bacon said, but if the aluminum ribbon touches the blade walls, there's trouble. There's a split blade too damaged to repair resting on the ground outside Bacon's shop.

The damage WindCom is repairing is from a storm that bombarded central Montana earlier this summer, Bacon said. This rolling grass range framed by the Crazy Mountains in the far south and the Little Belt Mountains to the northwest is the home of fierce wind, hot sun and winter days cold enough to crystallize a person's breath. Here, antelope outnumber people and the wind blows 40 percent of the time, two claims few places in America can match.

Most of the lightning that struck here in June wasn't strong enough to do damage, according to General Electric experts who use satellites to record each strike and measure its strength in joules.

Lighting repairs are fairly common, said Juan Borhez, WindCom composite project manager. Borhez is one of the engineers who design repair plans in Houston. What's unusual is making the repairs in the air. Other companies will do minor blade work in the air, but few, if any, will tackle jobs as technically demanding as lightning repair.

The platform the company uses is complex, Borhez said, designed to adjust to a wind tower's taper as it rolls up its side. A technician works the cable system that lifts the platform, and repositions it so the windmill blade eventually threads its center. There are also balancing weights that need constant adjustment to keep the platform level.

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