During the last few years damage to wind turbines due to lightning strokes has become an increasing problem. The increasing number and height of installed turbines have resulted in an incidence of lightning damage greater than anticipated with repair costs beyond acceptable levels. The influence of lightning faults on operational reliability becomes a concern as the capacity of individual wind turbines increases and turbines move offshore.
This is particularly the case when several large wind turbines are operated together in wind farm installations since the potential loss of multiple large production units due to one lightning flash is unacceptable.
Unlike other electrical installations, such as overhead lines, substations and power plants, where protective conductors can be arranged around or above the installation in question, wind turbines pose a different lightning protection problem due to their physical size and nature. Wind turbines typically have two or three blades with a diameter up to 100 m or more rotating 100 m above the ground. In addition, there is extensive use of insulating composite materials, such as glass fibre reinforced plastic, as load-carrying parts.
The lightning protection system has to be fully integrated into the different parts of the wind turbines to ensure that all parts likely to be lightning attachment points are able to withstand the impact of the lightning and that the lightning current may be conducted safely from the attachment points to the ground without unacceptable damage or disturbances to the systems.
To that end this report was developed to inform designers, purchasers, operators, certification agencies and installers of wind turbines on the state-of-the-art of lightning protection of wind turbines.
During the last few years, all major wind turbine manufacturers have made dedicated efforts towards developing adequate lightning protection systems, and the first experiences with these new designs are beginning to be seen. It is therefore reasonable at this time to consider and prepare for a standardization effort that will give both manufacturers and operators a common framework for appropriate lightning protection of wind turbines.
Prior to considering development of a full standard, the report looks at how to:
• Identify the generic problems involved in lightning protection for wind turbines
• Collect and systematize existing experience with both older and new designs of wind turbines
• Describe appropriate methods for evaluating the risk of lightning damage to wind turbines, thereby making reliable cost-benefit evaluations of lightning protection efforts possible
• Describe and outline appropriate methods for lightning protection of wind turbine components, considering the special nature of wind turbines and the extensive use of composite materials
• Compile a technical report outlining problems and solutions as seen today. The working group should identify and quantify areas where further research and proper standardization efforts are needed.
This technical report is structured as follows:
• Background on the current understanding on lightning phenomenology and its impact on wind turbines
• The lightning damage experience as extracted from the various national wind turbine databases
• Describes risk evaluation
• Discusses appropriate methods for protection against lightning damage
• Identifies areas for further research.