Iberdrola SA (IBE), the world's biggest renewable energy producer, has found that falling blades from a Suzlon Energy Ltd. (SUEL) generator at a U.S. wind farm was a one-off accident unrelated to the turbine's history of cracked blades.
"This type of failure is a singular event," said an Iberdrola report, a copy of which was mailed by Suzlon to Bloomberg News, on a joint investigation by the two companies into the incident.
Iberdrola suspended operations at the 150-megawatt wind farm in Rugby, North Dakota after blades from a Suzlon S88 turbine fell from their mount, the company said on March 21. The same model suffered cracked blades starting in 2007, which had prompted a $100 million global retrofit program by India's largest maker of windmills for power production.
The accident at Rugby was caused by the failure of a bolt connecting the rotor assembly to the nacelle, the report said. Stress may have been put on the bolt because of a misalignment of the connecting surfaces between the rotor hub and mainshaft flange, it said.
All 70 turbines and 3,360 bolts were inspected and seven bolts replaced as a precaution before Iberdrola and Suzlon agreed the site was safe to return to service, it said.
"Suzlon, who is permanently onsite, will perform additional checks in conjunction with regular maintenance activities," it said.
Suzlon has more than 2,000 sets of S88 turbines operating worldwide and its global fleet are performing above industry standards, spending only 3 percent in downtime for maintenance, the company said in an e-mail.
Suzlon shares plummeted 83 percent between the time it announced the defect in January 2008 and completed retrofitting in October 2009 as customers, including Rosemead, California- based Edison International (EIX), canceled orders.
Ahmedabad-based Suzlon, which expects sales this fiscal year to return to record levels reached before the global financial crisis, advanced 1.7 percent to 52.15 rupees at 10:52 a.m. local time in Mumbai trading. The benchmark Sensitive Index of the Bombay Stock Exchange gained 0.1 percent.
