| Overhead transmission lines are important parts of the power grid, and lightning strike is the main cause of transmission line faults, badly impacts the safe and reliable operation of the grid.Lightning overvoltage may cause insulator flashoverand other transmission line faults, such as line trip. And itbrings great difficulty to line inspection and maintenance work, especiallyin mountain areas with poor condition. Also, lightning invasion wave may cause damage to the equipments inside the substation, resulting in greater equipment accidents. Andsurge corona is the main factor resulting in the attenuation and distortion of lighting wave in the propagation process. When designing the lightning protection level of transmission lines and substationswithout considering the attenuation and distortionof lightning over-voltagewave caused by surge corona, high insulation level requirements for electrical equipments will increase cost. Therefore, study of propagation characteristics of lightning wave is necessary to the insulation level setting and insulation coordination improvement.This paper began with microphysical processes of corona discharge, includingionization, migration, recombination, attachmentand diffusionprocesses, andpresenteda hybrid algorithm for 2-D numerical model under impulse voltage. Optimized charge simulation method and finite element method were appliedrespectively to calculate the electric field on artificial boundary and the total electric field, while finite volume method was applied to calculate the continuity equation of electrons, positive and negative ions. And electric field distribution,corona current characteristicson the surface of conductorand effects of space charges on charge losses of lighting wave wereanalyzedby the numerical model finally.Based on the calculation results and generation and migration of space charges, the paper established asurge corona equivalent circuit model consisting ofseveral RC parallel branches and a nonlinear conductance branch, and model parameters werecalculated by the fitting algorithm. Based on the equivalent circuit model of surge corona, considering the process of generation and migration of space charges, a lumped parameter equivalent circuit model of transmission line was established. Based on the line model, this paper presented an analysis method of lightning wave propagation characteristics on overhead transmission lines, which was equivalent to the amplitude attenuation in the spatial domain and waveform distortion in the time domain. Distortion law of lightning wave propagation, and the influence of lightning polarity, wave head time and wire parameters on the propagation process of lightning wave were analyzed. Besides, the results were supported by the published experiments. |
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