Study On Lightning Transient Effects Protection Of Wind Turbines

It is highly possible for wind turbines being struck by lightning due to their geographic position, the height of their blades and others. After lightning stroke, the weak current control system of wind turbines are invaded by powerful lightning current which could result in failure of electronic equipment in wind tower. In addition, the most of wind turbines are operated in parallel model in which transmission lines and the grounding system of the wind turbines are connected to each other,so other wind turbines will be affected by lightning current if a wind turbine is struck by lightning. Therefore, proper lightning protection is important to ensure the safety of wind farm.In order to provide better lightning protection for the wind turbines, the electromagnetic transient effects of wind turbines struck by lightning are researched in the following four aspects: analyzing the present situation of lightning protection for wind turbines and its shortcomings; discussing the lightning transient effect of single wind turbine; studying the back-flow lightning surges in the wind farm;simulating lightning transient characteristics of wind turbines grounding system.In the first place, lightning hazards and the present protective conditions of the wind turbines are introduced, transient effects of wind turbines including transient uplift, lightning electromagnetic interference and back-flow lightning surges are also analyzed. In order to improve the lightning protection for the yaw bearing, shunt experiment of the telescopic equipotential bonding copper and the traditional brush was carried out. The protection effect of telescopic equipotential bonding copper is superior to the traditional brush which may be applied to the protection of the yaw bearing.In the second place, parameters of electric models for wind turbines are calculated according to the relevant formula. A complete model includes blade model, tower model, cable model, grounding device model, transformer model,lightning arrester model, which are established in EMTP to analyze lightning transient overvoltage and overcurrent in wind turbines. Simulation results show that:the overvoltage on the blade could reach the MV level, and the air-termination system and under wire are required; the overvoltage amplitude at both sides of the transmission line is higher which is prone to breakdown. Both sides of the transmission line need to install SPD. Counterattack is easy to occur when lightning strikes the lightning rod on the cabin,so it is necessary to increase the size of the lightning rod and so on. A secondary combination SPD could also be installed in the load side of the power supply circuit near the lightning rod.In the third place, the back-flow lightning surges in the wind farm are analyzed.The amplitude waveform of the high and low voltage side on the wind turbine's transformer which is near the lightning strike point are analyzed. Failure probabilities of lightning arrester are also calculated. Simulation results show that:the higher ground resistance, the higher failure probability of lightning arrester.At last, the influences of different factors on the grounding system of wind turbines are researched by means of frequency domain - time domain hybrid analysis method. The research results indicate that the ground potential increases with the increasing soil resistivity. In the case of typical double-layer soil, the ground potential is affected by the thickness of the top layer. Increasing of the size of the grounding device and installing additional horizontal grounding device will improve the lightning protection performance of the wind turbines.