Research Of The Index For Lightning Shielding Of Transmission Lines

Transmission line is artery of power system, its safety influent the stability of network and power supply. Up to now, most breakdown is happened in transmission lines and also most breakdown is trip which caused by lightning, especially in mountain. According to record, 50% of breakdown in power supply caused by lightning. At the same time, because of the exacerbation of environment, times of trip caused by lightning become frequent, lightning trip not only influent running of equipment but also daily production and living. So lightning protection of transmission line become hot issues in field.This paper mainly stresses on theoretical studies and applications in parameters which influence lightning protection level of transmission lines.1. Build lightning over-voltage mathematical model through studying mechanism of lightning.2. The main methods to evaluate the characteristic of shielding failure for transmission line are the standard method, leader progression model (LPM) and electric geometry model (EGM). The electric geometric method relates the lightning discharging characteristic with structural dimension of towers together, and "striking distance" is introduced to describe the object's lightning attracting ability. It is much more advanced than the traditional method. With the development of EGM, many scholars proposed different calculation expressions and methods for "striking distance". Based on the principle of EGM, the expression for "striking distance" of IEEE working group commended is adopted, and then the arithmetic of space subdivision which conformed the realistic process is selected to simulate the process of lightning. Based on these studies, the emulation assess index of lightning protect level is build by researching standard method and EMG After calculating the actual transmission lines, the results of index is corresponded with real breakdown results.3. Compile lightning-protection emulation index software by using Visual Basic 6.0 as program development tool, users can input the data of towers and get the lightning-protection emulation assess by score.