Research On Lightning Transient Characteristics Of Vertical Axis Wind Turbines

As the energy problem becomes more serious,wind energy,as a clean and renewable energy source,has attracted worldwide attention.The objective conditions of wind turbines make it vulnerable to lightning accidents.Overvoltage and high current can threaten the normal operation of equipment and power supplies.Lightning strikes are an important factor threatening the safe operation of wind turbines.When lightning strikes the wind turbine,a large surge current flows through the fuselage,causing the transient potential of the wind turbine to rise.However,there are few researches on lightning protection of vertical axis wind turbines.In this paper,the representative Darrieus Φ-type wind turbine among vertical-axis wind turbines are the research object,and the modeling and lightning protection of vertical-axis wind turbines are deeply studied.First,a complete circuit model including blades,cables,struts,main shafts,towers,grounding devices,generators and converters was established.Taking into account the fluctuation characteristics of the lightning current,the segmentation processing is carried out when modeling the blades,towers,and grounding devices.In the calculation of blade electrical parameters,compared with traditional fan modeling that only considers power frequency or DC resistance,this article considers that the Darrieux Φ fan is a double convex blade type,which is divided twice according to the angle of the blade curve.The parameter algorithm uses the average potential method.The model of the tower fully considers its geometric shape and decomposes it into a series of horizontal and vertical multi-conductor systems.The coupling between the tower conductors is considered in the calculation.In the calculation of the grounding device,the ionization of the soil is equivalent to the increase of the radius of the grounding conductor,and the parameters are dynamically modified according to the current of each branch,which improves the calculation accuracy.Secondly,use ATP-EMTP software to analyze the lightning transient characteristics of blades,bearings,towers,and unit transformers.The modeling conditions include different lightning current waveforms,number of cables,ground resistivity,lightning strike points,and blade shapes.The calculation results show that the voltage rise of the vertical axis wind turbine is positively correlated with the change of the potential amplitude.When the lightning current amplitude remains unchanged,the shorter the lightning current wave front time,the more serious the waveform oscillation;the vertical axis wind turbine cable has a certain degree of Shunting effect.Appropriately increasing the number of cables can accelerate the discharge of lightning current;a good grounding system is conducive to reducing the overvoltage on the fan;the location of lightning strikes has a significant impact on the overvoltage of the fan,and the lightning protection of vertical axis fan blades should focus on the bulge of the blade position.Finally,some lightning protection measures for vertical axis wind turbines are proposed.This article proposes a method of installing ferrite magnetic ring devices on the blades,which can prevent the propagation of high-frequency lightning waves and effectively suppress the amplitude and steepness of the overvoltage on the blades.The influence of lightning transient overvoltage on wind turbines before and after the addition of the arrester is discussed.Through the simulation study on the protection distance of the arrester,the coordination curve of the protection distance of the arrester,the amplitude of the lightning current and the grounding resistance is obtained.The influence of common grounding and independent grounding on the potential of the wind turbine transformer and tower foundation is analyzed.Several methods to reduce grounding resistance are proposed,including appropriately increasing the number of cables,good grounding,and selection of grounding points.