Wind turbines are often struck by lightning because of their special shape, their tall structure and their beingplaced in the open air. Besides seriously damaging the blades, lightning results in accidents in which low-voltageand control circuit breakdowns frequently occur in many wind farms worldwide. Although some reports, such as IEC TR61400-24 and NREL SR-500-31115, have indicated a methodology for protection against such accidents, a standard solution to these problems remains to be established. The author, focusing on a method for protection of low-voltage and control circuits in a wind tower, proposed a new lightning protection system with two ring-shaped electrodes attached to the wind turbine. The proposed system has two ring-shaped electrodes of several meters diameter, one vertically attached to the nose cone and the other laterally placed at the top of the wind tower lying just below the nacelle. The pair of rings is arranged with a narrow gap of no more than 1 m in order to avoid mechanical friction during rotation of the blades and the nacelle’s circling. When lightning strikes a blade, the current reaches the upper ring from a receptor through a conductive wire. Then, the electric field between the two rings becomes high and finally sparks over and the lightning current flows downwards. The current propagates along the lower ring and the grounding wire, which is arranged outside of the wind tower rather than inside, and is safely led to a grounding electrode placed far enough away from the tower’s grounding system. In this paper, the author describes a basic experiment using a 1/100 downsized model, and also discusses the concept behind the present system. The result of the downsized experiment provides evidence of an effective advantage for lightning protection. 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
The installation of wind turbine has grown explosively worldwide; however, problems regarding interconnectivity to grids have arisen. It has also been pointed out that wind power generation facilities are exposed to lightning damage owing to their configurations, and so protective measures different from those needed for conventional generators are necessary. This problem has recently surfaced as an important issue [1–7].Japan, especially suffers from frequent and heavy lightning strikes, an example being the notorious ‘winter lightning’ found in coastal areas of the Sea of Japan. Indeed, many turbines in Japan have been hit by lightning, and winter lightning poses a specific threat due to its intense power and electric current which are much higher than the world average [7,9]. Although some of the above-mentioned reports describe these incidents and methods of protection, there appear to have been few investigations into insulation schemes, lightning protection design and transient analysis for the latest generation of apparatus. While blade protection has been relatively well discussed , the behavior of the wind turbine experiencing surge propagation during a lightning stroke has yet to be clarified.
There is room for more work to be done in this area. In general, lightning protection for wind power generation includes a lightning pole on a nacelle, an independent lightning pole tower and a receptor on the top end of a blade. But the lightning pole on the nacelle cannot obtain enough height owing to weight and wind pressure, and an independent lightning tower greatly increases the construction costs.
Though the third solution, the receptor on a blade, recommended in IEC61400-24 , appears the best solution for lightning protection, it is not a complete solution. Despite the existence of such receptors, dielectric accidents still occur on wind power turbines including blades, the generator, the transformer and lowvoltage circuits .
According to an IEC report , the most frequent accident is dielectric breakdown on low-voltage circuits including electric and telecommunication equipment. In general, electrical and electronic equipment for wind power generation are set up close to or inside a wind tower. Once lightning strikes the wind turbine, assuming that it hits a receptor of one of the blades, a lightning current surge propagates through a down-conductor in the blade, a carbon brush or arc horn near the bearings,and the grounding conductor inside a wind tower (or,in another case, the current may flow through the conductive tower itself). The low-voltage circuit in the wind turbine is easily broken by electromagnetic induction in such a situation. Considering the above, the author proposes a novel lightning protection system that has two ring-shaped electrodes. The principal concern of the proposed system is to prevent the lightning surge from affecting the wind turbine as well as the nacelle and the tower.
This paper discusses an impulse experiment utilizing the proposed system in a downsized wind tower accurately simulating an actual 2 MW wind turbine on a 1/100 scale. Attaching the proposed ring-shaped electrodes to the downsized wind turbine, the author demonstrates that the system provides effective lightning protection.