| Most of low-pressure transmission line's fault and trip and high-pressure transmission line's insulation aging are caused by lightning induced over voltages, which is 90% of the total lightning. Induction lightning over voltages along the lines will seriously affect the power quality and the normal operation of secondary equipment. The calculation of lightning induced over voltage in overhead transmission lines is the basis of power line insulation and lightning protection design.Firstly, this paper use an approximate formula method to calculate the horizontal electric field at a point in space. A basic lightning model is built, and according to the modeling assumption, the two components(one due to the return stroke charge and the other due to the return stroke current) generated by a trapezium wave are derived. Superimpose the two components derived the horizontal electric field. Any arbitrary current waveform can be represented by the superposition of a set of trapeziums so we can get the electric induced by any arbitrary current waveform. In the process, we considered the soil conductivity's influence, and also analysis the factors that impact the electric field.Then, this paper establish the time domain integral equations of horizontal electric field coupled with a single thin wire. The horizontal electric field can be seen as the incident field in the time domain integral equations. Apply moment method to this equation in space and time discretization. Use time stepping algorithm to solve the obtained linear equations. In this process, the article have discussed the principle to chose the basic functions and weighting functions, and improved the stability of time stepping algorithm.The impact of the earth and lines under load have been discussed. At last, some calculation samples are presented. The results agree well with relevant literatures, the feasibility of the method is demonstrated. In addition, the lack of job and the aspect are presented. |
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