Study On Lightning Protection Performance For 500kV Double Circuit Transmission Line

Obtained by EMTP program and the EGM, this paper studies on lightning protection performance on 500kV double circuit transmission line The distributed parameter model of tower is built when analyzing the back stroking lightning protection performance for double circuit line, It can truly reflect the spreading course of lightning current on the tower, furthermore, considering the randomness of working voltage's phase when lightning strokes the top tower and supposing the probability of lightning appearing arbitrary phase in a cycle of AC is equal, this paper brings forward the statistical method to calculate the rate of back stroking on double circuit line. It also improves the EGM by considering the effect of wind speed when analyzing the lightning protection performance of shielding failure and designs a practical engineering program to calculate the lighting shielding failure rate. This can fully consider the effect of the structure of transmission line and the selection of lighting parameter etc. By calculating and analyzing various of factor that affect the lightning tripping probability of 500kV double circuit transmission line, we can draw the conclusions: the result by intersecting method is more accord with the practicality circumstance than by existing standard methods, using unbalance high insulation and reverse sequence of wire can reduce the contemporary outage rate of double circuit line, reducing the footing resistance is one of the most efficiency method to reduce the back stroking rate of double circuit transmission line, the double back stroking rate and the single back stroking rate will fall by three ground wire, when the footing resistance is 10 ohm, the back stroking rate by three ground wire is 83 percent of by two ground wire. It is importance to accurately conform the wave impedance of tower, when the wave impedance of tower change sign 10 percent independently, the back stroking rate of transmission line will change sign 20 percent accordingly. Ground obliquity is the main factor that affect the shielding failure rate of line, when the ground obliquity increases, the shielding failure rate will increase nonlinearly. The wind speed must be calculated when analyzing the shielding failure performance by EGM, becauseit can affect the result of shielding failure rate of double circuit line. The tower is lower, the double circuit outage rate of transmission line is lower. The β factor must be strengthen study for exceed or special high voltage level transmission line. The meanwhile a proper lightening resisting measure is presented. These results will propose reference for the same type of transmission line.