Study On Charge Distribution Model And Related Parameters Of Lightning Channel

In recent years,due to lightning-caused by power system outages,casualties and accidents occur frequently,so it is essential to predict and protect against lightning.In the simulation of the lightning channel development process,the charge distribution in the lightning cloud and the channel will affect the electric field distribution in space,and then affect the path of downward leader development.Existing research think there are three primary channel charge distribution model: uniform distribution,exponential distribution,and linear distribution,early by lightning the limitation of experimental conditions,the above three kinds of distribution is a kind of speculation at present,there are no people to fully demonstrated with experimental results,so the lightning channel charge distribution is worthy of further study.The development of lightning channel has the characteristics of step discharge,which is similar to the charge-discharge process of resistance and capacitance circuit.Based on the calculation of the equivalent capacitance of each channel,the equivalent circuit model is established and studied in this paper.This paper is mainly developed from the following aspects:Due to the limitation of the charge distribution model proposed in the current lightning research,an equivalent resistive and capacitive circuit model is proposed based on the cascade characteristics of lightning development.The channels are segmented,and each segmented channel’s generation is considered an independent discharge process of the resistive and capacitive circuit to reflect the independence of each segment.According to the boundary conditions of charge and voltage when the channel is in a steady state,combined with the theory of electrostatic field,the equivalent capacitance and resistance matrix are obtained by calculating the potential coefficient of each channel in Matlab.The change rules of selfcapacitance and mutual capacitance in the capacitance matrix are explained by combining them with the development process of lightning.Finally,based on the equivalent parameters obtained above,an equivalent circuit model for the step-by-step development of the channel is built in the electromagnetic simulation software Emtp.Based on the equivalent circuit model built-in Emtp,the voltage change curve of the channel is simulated step by step,and compared with the calculated results in Matlab,the reason for the channel voltage change is studied.Based on the simulated equivalent capacitance and steady-state voltage,the change of charge distribution in the channel during lightning development is calculated,and the changing trend of charge in the channel is explained from the discharge process during lightning development.According to the charge distribution in the channel,the variation of electric field intensity around the channel is calculated.Its variation trend is consistent with that of the charge in the channel.Since the electric field intensity around the lightning channel determines the path selection during its development,it is a very important physical quantity,but no research has measured the electric field around the channel.Based on the similarity between lightning discharge and long gap discharge,a 10 m rod-plate gap discharge model is built in Comsol in this paper,and the electric field intensity range around the rod electrode is calculated and compared with the electric field intensity around the channel calculated by the model built in this paper,which initially demonstrated the rationality of the model built in this paper.Based on the measured ground electric field and the charge density curve in the channel when lightning occurs,the rationality of the model established in this paper is further demonstrated.However,both the simulation verification based on rod-plate gap discharge and the measured data verification are different from the model established in this paper,and the necessity of parameter optimization is illustrated.Based on the streamer theory to explain the lightning discharge process,three main parameters affecting the channel charge quantity,charge density,and surrounding electric field intensity during lightning discharge are defined: equivalent sphere radius,step size,and charge loss.The variation trend of channel self-capacitance,charge quantity,charge density,surrounding electric field intensity,and ground electric field intensity are studied when the above three parameters are changed.The effect of each parameter is obtained and compared with streamer theory.The reliability of the equivalent circuit used to explain the lightning discharge process was proved.In addition,based on the rod-plate clearance and the ground electric field,the appropriate value ranges of the three parameters under different heights of thunderclouds are explored.It is found that the radius and step length of the lightning tunnel change dynamically with the development of the tunnel towards the ground.In this paper,the influence of dynamic parameters on charge distribution and electric field intensity is studied,and the recommended parameter range and lightning channel charge distribution model are given.Finally,the application of the model in lightning path simulation is demonstrated.