Simulation Of Lightning-Induced Voltages Over Stratified Conducting Ground

With the rapid development of urbanization and industrialization in modern social, lightning threats to the human activities are getting more serious, especially to the power system. Therefore, an in-depth research on the lightning-induced voltages on the overhead transmission lines has great theoretical significance and practical value. Based on the transmission line theory, the Agrawal coupling model has been derived. Then the lightning-induced voltages are calculated using the FDTD method. As a validation, the results of the LIOV program are applied and in a good accordance with the results of the FDTD method. Finally, the effect of return discharge parameters, transmission line parameters and the propagation path on the lightning-induced voltages has been discussed. Main conclusions are as follows:(1) The lightning-induced voltage is composed of the scattered voltage and the incident voltage. The incident voltage is always positive, while the scattered voltage maybe positive, bipolar or negative. With the observation point moving from the mid-point to the end-point, the contribution of the incident voltage to the total voltage is getting smaller.(2) In the lightning discharge parameters and the transmission line parameters, only four parameters have great influence on the mid-point voltage. They are the peak value of channel-base current, the velocity of return stroke, the height of transmission line and the distance between the line and the striking point. Besides these four parameters, the current rise time, the terminal resistance and the length of the transmission line also have great influence on the end-point voltage.(3) When the lightning electromagnetic wave propagation along homogeneous lossy ground, the lightning-induced voltage at the mid-point of the overhead transmission line shows a positive and unipolar waveshape, while the lightning-induced voltage displays a bipolar waveshape at the end-point of the transmission line. With the decrease of the conductivity, the peak value of the mid-point voltage and the initial negative peak of the end-point voltage both increase, while the positive peak of the end-point voltage decrease.(4) If the soil is divided into two horizontal layers and the upper layer is less conductive than the lower layer, the lightning-induced voltages are initially determined by the upper soil and later follow the characteristics of the lower layer. If the upper layer soil is more conductive than the lower layer, the induced voltage waveforms are close to the one that would be produced by the ground as homogeneous with the parameters of the upper layer. When the soil conductivity vertically stratified and the first layer is more conductive than the second layer, the positive peak of the mid-point voltage and the negative peak of the end-point voltage decrease with the increase of the distance between the lightning channel and the overhead transmission line. However, if the first layer is less conductive than the second layer, the lightning-induced voltage waveforms are mainly determined by the second layer soil and virtually no influenced by the first layer soil.