Studies of lightning protection design for wind power generation systems in Japan

SUMMARY Recently, wind power generation systems have drastically increased in Japan. As the increase of the wind power generation systems, outages of these systems by lightning have also increased and establishment of effective protection methods is strongly required. New Energy and Industrial Technology Development Organization (NEDO) in Japan has published a guideline for lightning protection of wind power generation systems based on the field observations and model experiments. Furthermore, many researchers in Japan have studied effective methods to reduce lightning damages of wind power generation systems. The results of these studies are summarized as follows. 1) Most of damage of wind turbine blades has been caused by lightning that occurs in the coastal area of the Sea of Japan in winter season, what we call ‘winter lightning’. 2) In the case of the winter lightning, charge transfer exceeding the value of 300 C, which is the maximum value shown in an IEC Technical Report on lightning protection of wind turbines, often occurs. 3) Model experiments of lightning attachment shows that though the disc-type receptor is one of effective methods to prevent the damage of wind turbine blades by lightning, discharges cannot be always intercepted by receptors. On some conditions, lightning hits the blade and causes damage. The breakage characteristics of wind turbine blades are also clarified from the large current experiment. 4) Surge analysis shows overvoltage characteristics inside the wind power generation systems when lightning strikes a wind turbine and effective protection methods and grounding systems to reduce the overvoltages are proposed. 5) A hazard map for wind power generation systems in Japan has been constructed and a cost-effective protection scheme has been proposed based on the concept of lightning risk management.