Study On The Lightning Protection Performance Of Transmission Line

The lightning's stroke on transmission line is principle reason for outage . The accident caused by thunder is above 50 percent in the outage of electric power system ,so it is very meaningful for system service and stable operation to evaluate the line lightning protection performance.A improved EGM is adopted to calculate the transmission line shielding failure rate in this paper. In the course of calculation, a wind deviation angle is taken in for considering the effect of wind. At the same time, a coefficientβ, which varies with tower height h and is the ratio of two electric intensities when lightning strikes on transmission line and on ground, is introduced in this paper. The uncovered-arc-method is adopted to calculate every line's rate of shielding failure. It takes the current of lightning when the length of uncovered arc is zero as the largest thunder current of shielding failure.The Bergeron-method which is used to solve the wave course of distributed parameter and the trapezoid-method which is used to compute the lumped parameter circuit are adopted in this paper ,on purpose of calculating back striking rate. Electricity parameters of grounding device are equated to reflect the effect of soil breakdown . The way used in this paper can factually reflect the spreading course of lightning current in the system of tower and grounding device and line.A program, which can be used to calculate shielding failure rate and back striking rate, is written, aiming at 500kV double-circuit transmission line. The effects of wind deviation angle and tower structure.etc. on 500kV double-circuit transmission line's shielding failure , are analyzed. The effects of soil resistance rate, wave profile of thunder, steepness of wavefront, wavespeed, foreword, insulation way, etc. on back striking are analyzed, too. The results illustrate that the bigger the wind deviation angle ,the bigger the rate of shielding failure, and the longer the distance of two protection lines, the bigger the total rate of shielding failure . The relation between every line's rate of shielding failure and tower structure is complicated , so it is needed to calculate and analyze concretely. The results also indicate that the higher the soil resistance rate, the lower the protect level, and the steeper the wavefront, the lower the protect level, and the smaller the wavespeed, the lower the protect level. Non-balance high insulation can reduce double-circuit line outage in the meantime obviously.