Document Type:Issues & Overviews
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Wind turbine systems have been advancing rapidly over the last several years, with many systems reaching or exceeding five megawatts (MW). These larger systems include wind turbine blades up to 200 feet (61 meters) long and weighing several tons. Maintenance costs for these wind turbines are high and the blades can be damaged by manufacturing and in-service defects, environmental degradation, fatigue, and lighting strikes. Many wind farm operators have been relying on inspection approaches that involve shutting down the wind system so that personnel can visually inspect the blades from scaffolding or hydraulic lifts or by rappelling down the blade surface. These inspections are challenging, expensive, highly labor intensive and may not provide reliable results since many structural defects in wind turbine blades are below the surface. If left undetected, these faults can degrade the blade to the point where it must be replaced at a cost of $300,000 to $700,000. In addition, shutting down one or more turbines for an uptower inspection or replacement reduces the net generating capacity of the wind farm.
EPRI has been conducting research on an advanced wind turbine blade inspection approach using non-destructive examination (NDE) techniques and was looking for a host site for field demonstrations. Since 2007, Duke Energy has been actively involved in growing its wind energy portfolio. Duke Energy Renewables owns and operates more than 1,600 MW of wind power and expects to bring another 250 MW online in 2015. The company hopes to grow its wind business to between 5 and 7% of its total generation. The company agreed to be the host site for field testing the SABRE™ Wind Turbine Inspection and Data Management System at its Los Vientos wind farm in southern Texas.
The SABRE™ system has several advantages over conventional inspection techniques for large wind turbine blades. The system inspects blades from the ground while the blades are operating. It includes a specialized, long wave infrared (IR) camera to detect slight IR emissions from structural anomalies in the rotating blades that show up as hot spots or cool spots. Acoustic spectral analysis technology uses broadband high sensitivity microphones to detect and locate lightning strike holes, cracks, and irregular surfaces. The system also includes phase imaging photography that can detect surface anomalies. The system is mounted on a sport-utility vehicle that can travel around a wind farm to inspect multiple blades and can usually inspect three blades on one turbine in less than 30 minutes.
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