Simulation Of Lightning Electromagnetic Environment On Complex Ground And Lightning Induced Voltages On Overhead Transmission Lines

The damages of lightning electromagnetic impulse(LEMP)to the social electronic equipments, communication systems and power systems are getting worse. In consequence, looking into the LEMP’s transmission property in space and the coupling problem on the transmission line of LEMP is very important in the theories and practical application of lighting protection. Firstly, the paper studies the propagation characteristic of lighting return stroke under complex surfaces, discussing the influence of smooth and rough surface on the return stoke electromagnetic fields based on two-dimensional fractal rough model, meanwhile, on the basis of the soil model proposed by Scott, the paper analyzes the influence of lightning return stroke electromagnetic fields caused by the change of the electrical parameter owing to the different soil moisture. Then, we take advantage of the method of FDTD and the transmission line coupling model to analyze the induced over-voltage characteristic of lightning return stroke electromagnetic field sensor on the transmission line in case of ideal surface and vertical and horizontal stratification of the ground conductivity. The conclusions are as follows:(1)When the horizontal electric field from lightning spread along the rough land surface, it is of great influence to the electric field according to the surface roughness level. With the increase of the roughness, the negative peak in initial stage of horizontal electric field diminished; But when the horizontal electric filed from lighting spread along the complex surface in the land-sea connecting belt, the influence by the terrestrial part of the roughness is more obvious than the undulate of the waves as to horizontal electric field.(2)When the electromagnetic field spread along the surface with0.2%and10%of the soil moisture, the impact of the former one(0.2%of the soil moisture) is more obvious to the electromagnetic field, especially to the horizontal electric field from lightning, which reflected in the peak of the horizontal electric field is inversely proportional to the soil moisture. When the soil moisture increased from0.2%to10%, the rise of the vertical electric field and the horizontal magnetic field decreases with time; the impact of the influence to the peak of the vertical electric and magnetic fields is not obvious.(3) In case of an ideal ground, the induced overvoltage on overhead line increases with the increase of the speed of lightning return stroke and the altitude of the overvoltage on overhead line, decreases with the decrease of the distance from the overhead line to the point of strike. Different lightning return stroke models has little effect to the peak of the induced overvoltage, but mainly affect the rising and falling edge time of the voltage waveform, as that influences the attenuation speed.(4)In the vertical stratified conductivity situation, Inductive over-voltage values are affected by the conductivity of the smaller segment is more obvious. For the sake of the smaller the conductivity is, the greater the electromagnetic field attenuation, especially to the horizontal electric field. In the horizontal stratified conductivity situation, the lightning induced over-voltage is mainly affected by the upper conductivity, moreover, when the upper thickness is greater than15meters, the lower conductivity of the impact of over-voltage is gradually increasing.