| Wind turbines are often located in open areas,the height of which can reach more than100 m,easy to be struck by lightning.Lightning is one of the important causes of fan failure.Accurate lightning current waveform data is an important basis for fan failure analysis and protection reform.Steel fan tower is the only channel for lightning discharge.Its diameter is up to 4m,so it is difficult to measure the current directly by means of Rochs coil.The non-contact current measurement technology based on magnetic sensor array has certain feasibility.It is of great theoretical significance and engineering value to study the measurement method of fan lightning current with simple structure and high inversion accuracy,and to develop a small volume and wide band inversion measurement system of fan lightning current.In this paper,the inversion measurement method of fan lightning current based on biaxial magnetic sensing array is studied,a biaxial tunnel reluctance sensing array measurement system is developed,and lightning current measurement experimental verification is carried out for the reduced fan model.The specific contents are as follows:(1)the fan for cylindrical thin shell structure,tower drum tower drum magnetic field distribution of lightning current can approximate to find the solution for long straight conductor line current,any two points outside the tower drum is analyzed the relationship between electromagnetic field and current tower drum,magnetic sensor array is proposed based on two-axis fan lightning current inversion method of the lightning current inversion formula is deduced,research the position sensing probe space layout of the effect of inversion error.(2)established the lightning transient calculation model of wind power generator,lightning location is studied and the lightning current waveform parameter of the transient magnetic field and current distribution around the fan characteristics,based on the inversion method proposed in this paper,the analysis of the magnetic field sensing probe layout deviation,the relationship between height and inversion results put forward the best installation location sensing probe,At the same time,the validity of the inversion calculation method is verified.(3)analyzed the principle and advantages and disadvantages of various magnetic resistance sensor,choose the appropriate tunnel magnetoresistance sensor element,the biaxial sensing probe design,design of signal conditioning circuit,power circuit design,completed the biaxial tunnel magnetoresistance sensor array based lightning magnetic field measurement system is developed,and the experimental measurement system performance test.(4)A 1:50 scale wind turbine lightning current measurement experimental platform was built,and the response characteristic experiments of the measurement system under different lightning current amplitudes were carried out,and the lightning current measurement error characteristics under different installation positions of the measuring probe relative to the tower cylinder were studied,which verified the accuracy and reliability of the measurement system.The results show that this method only needs a pair of biaxial tunneling magnetoresistance sensors to accurately invert the lightning current of the fan,and the inversion accuracy is less affected by the spatial location of the sensors.Under the reduced experimental conditions,the lightning current measured by the measuring system and the actual reference current are basically consistent in the wavefront time,half peak time and waveform steepness,which can meet the frequency response requirements of the lightning current measurement,and can realize the accurate measurement of the lightning current waveform.Under the condition that the distance between the two measuring probes is fixed,the measurement error of the amplitude of the system is less than 6.08% relative to the horizontal or vertical movement of ±15mm.The system has the advantages of simple structure,small volume,high precision,convenient installation and wide band,which can meet the requirements of lightning current measurement.The research provides an important theoretical basis and technical support for the wide application of the fan lightning lightning transient current measurement system. |
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