Lightning protection of wind turbine generation systems

The lightning damage poses a problem with global spread and enlargement of wind power generation systems. Especially a lightning stroke to the blades of a windmill does serious damages, such as an destruction and falling of a blade. The generating mechanism of damages and effective lightning protection methods are studied taking the lightning with abnormally large energy into consideration. Special attention should be also paid to outages of connecting lines to a windmill due to backflow currents from a windmill side.