Research On Lightning Protection Of Off-shore Wind Turbine Generators

With the increasing of offshore wind turbine unit capacity and the height becoming higher, the risk of wind turbine in the marine environment being struck by lightning is greatly increasing. Due to high operation and maintenance costs of offshore wind turbine, it puts forward a higher requirement on the reliability. Offshore wind turbine lightning protection is an important issue to be concerned, related research having important theoretical and practical significance for the offshore wind farm design and safe operation.This paper carried out studies from characteristics of the offshore wind farm collection system lightning overvoltage, grounding technology of wind turbines, and lightning attachment characteristics of wind turbine blades, summarizing the main developments as follows:For lightning damage phenomenon of the wind farm collection system arrester and the WTG step-up transformer, collection system lightning overvoltage numerical calculation was carried out, consisting of a single wind turbine or multi wind turbines and submarine line connected, and distinguished three kind of types layout including the WTG step-up transformer being arranged in the tower and tower bottom. Studying the lightning current amplitude, the lightning current waveform, impulse grounding resistance of the wind turbine as well as the cable sheath grounding and other factors affecting offshore wind farm collection system lightning overvoltage, the damage mechanism of lightning arrester of the wind farm collector system caused by lightning stroke was revealed, the offshore wind farm collection system lightning overvoltage protection wiring way, arrester configuration and recommended values of the nominal discharge current as well as suggestions of insulation coordination were proposed.Offshore wind turbine foundation is restricted by terrain conditions, as well as the difficulty of construction. Whether the grounding performance meeting the system fault and lightning protection requirements is an important question need to answer for designing. In this paper, aimed at three basic forms of wind turbines including single pile foundation, three footing foundation and gravity type foundation which were most often used in the intertidal zone and offshore wind farm, the calculation model considering the seawater, clay and gravel layer structure was established, the numerical calculation of the offshore wind turbine grounding device of power frequency parameters and impulse parameters were carryed out, the influencing factors of offshore wind turbines grounding features such as the water depth, soil resistivity and thickness of clay layer, gravel layer soil resistivity and basic structure size parameters were analyzed, the key mechanism of seawater effect was revealed, and the offshore wind turbine grounding safety was evaluated. The research results provide the basis for offshore wind turbine generator grounding design.Discrete lightning receptors are usually arranged on blades in modern wind turbines, lightning damage to wind turbine blades is the common accident in the wind farm, and design of the lightning receptors is different for different wind power equipment manufacturers due to lack of standard rules. The effect of lightning receptor arrangement on the lightning attachment characteristics and lightning probability is the basis issues worthy of study. In this paper, lightning attachment characteristics test method of the typical structure of offshore wind turbine blade was proposed, lightning attachment characteristics test respectively on 40m and 70m scale models were carried out, quantitative data about the receptors arrangement forms, number of lightning receptors on blade lightning attachment and lightning probability were achieved, and optimization method of lightning receptors arrangement on wind turbine blades was proposd.