Optical Current Sensing Technology For Lightning Current Measurement Of Transmission Line

Lightning current parameters are the basis of lightning protection design.Lightning current parameters can be used both in the big data statistics of the area to provide a basis for differentiated lightning protection,and can also be used to analyze the fault location of the lightning strike and to determine the type of fault,which can guide the maintenance of a single accident.The existing lightning current measurement structure has simple functions and the measurement devices have certain limitations in principle,making it difficult to obtain accurate and comprehensive lightning current parameters.This results in only a few statistical parameters such as lightning current amplitude and steepness being used in a large number of statistics,which is not conducive to formulating a perfect lightning protection scheme.For this situation,this paper uses the advantages of optical current sensing,natural insulation,no bandwidth limitation,and no magnetic saturation to study the key technology used in the measurement of transmission line lightning current.This paper study the optical current sensing technology from the three aspects of the lightning current distribution of transmission lines,the magnetic resistant method and the sensitivity optimization of the sensing unit in light of different lightning fault characteristics in combination with actual measurement requirement.In order to solve the problem that the existing sensor unit layout theory does not support the multifunctional lightning current measurement technology,the lightning current distribution characteristics of towers and lines is studied,a measurement structure with functions of accurate measurement of lightning current waveform,measurement of fault parameters,and judgment of typical lightning strike types is proposed.The structure is composed of a waveform sensing unit and a parameter sensing unit,and the two sensing units are arranged on the tower in their respective measurement forms.Considering that the tower itself interferes with the waveform measurement,a lightning current distribution model of the tower is established.The influence of the wave process of the tower on the lightning current measurement is studied,and a measurement form of the waveform sensing unit is proposed.According to the characteristics of the current distribution under different lightning conditions,a measurement form of the parameter sensing unit is proposed.It has the advantages of large measurement range and many parameters(including key parameters of line lightning current and flashover current).Combining the measurement form characteristics and response characteristics of the two sensing units,a judgment method of typical lightning strike types is proposed.The multiple shunt channels formed by the lightning strike transmission line will generate different magnetic fields,which will cause interference to the sensing units at different measurement positions.For this,this paper establishes the magnetic resistant model of the waveform sensing unit and the parameter sensing unit.According to the magnetic field characteristics of the tower lightning current and the response characteristics of the sensing unit,two spatial magnetic resistant methods of the sensing unit are proposed.A model of the magnetic field interference degree of the lightning current is established,and a method for evaluating the magnetic field interference of the sensing unit is proposed.The result of finite element magnetic field simulation shows that when the sensing unit adopts the magnetic resistant method to measure the lightning current,the anti-magnetic field interference ability can be significantly improved.Aiming at the problem of low sensitivity of point optical sensing structure,the sensitivity optimization scheme is proposed.According to the composition characteristics of the optical path of the sensor unit,the sensitivity model of the sensing unit is established,which revealed the influencing factors of the sensitivity of the sensing unit.For the lightning current measurement requirements of the waveform and the parameters sensing unit,the sensitivity optimization method of the sensing unit is proposed combined with temperature,light coupling efficiency and other influencing factors from three aspects: the size of the sensing unit,the spatial measurement position and the magneto optical material.The result of line magnetic field simulation verified the feasibility of the optimization scheme.The design schemes of the waveform sensing unit and the parameter sensing unit were formulated,and the sensing performance of the sensing unit was verified.The optical devices and corresponding parameters of sensing units were selected and designed.The experimental platforms of sensitivity,temperature,and impulse current experiments were built,and a response performance experimental analysis of the sensing unit was carried out.The results show that the two sensor units designed in this paper can meet the sensitivity and temperature stability requirements,the optical current sensing technology can accurately measure the key parameters such as the amplitude,steepness and waveform of the impulse current,that can provide effective support for the measurement of lightning current full waveform and lightning positioning of transmission lines.