Lightning knocked out two wind turbines and sent a massive tower blade crashing to the ground at the Judith Gap Wind Farm last month, the company said Wednesday.

Repairs began earlier this month and will continue into September, said Susan Dennison, an Invenergy spokeswoman.

No workers were on the site at the time of the accident, which occurred at 6:20 p.m., she said.

"There are lightning strikes on a regular basis," Dennison said. "This one just happened to be pretty severe."

The 90 towers at the 135-megawatt wind farm, located on 8,300 acres of private and public land 125 miles southeast of Great Falls, are 262 feet tall. The blades are 127 feet long.

Lightning struck Turbine No. 88's three blades, and one disengaged and fell to the ground, Dennison said. The blade struck and dented the steel tower during the drop, she said.

All three of the tower's blades and its rotor will need to be replaced, Dennison said.

Technicians with General Electric Co., which manufactured the towers for wind farm owner Invenergy, began working on the repairs July 10. On Wednesday, the technicians were preparing to remove the rotor with the help of a large crane, she said.

Judith Gap began upgrading its lightning protection system for each tower last winter, but the system hadn't been installed in No. 88 at the time of the storm, Dennison said.

Turbine No. 7 also was struck by lightning, but had the new protections. Damage was minor, Dennison said.

No cost estimate of the repair work was available, she said. The $180 million wind farm opened for business in January 2006.

Each wind tower can produce a maximum of 1.5 megawatts for a total potential output of 135 megawatts. Since the storm, both towers have been idle, Dennison said.

After the strike, a computer monitoring system alerted employees, who showed up to secure the area and notify host landowners.

Invenergy leases private land from area farmers and ranchers and from school trust land managed by the state Department of Natural Resources and Conservation.