Research On Calculation Of The Lightning Induced Overvoltages And Protection Of Power Distribution Lines

The most part of the distribution lines are exposed in the air, so they are apt to be damaged by lightning overvoltage, which will interrupt power supply and affect uses’ production and lives. Researches indicate that the main factor of lOkV overhead distribution lines’insulator flashover or lines faults by lightning is induced lightning, the proportion of the faults by induced lightning exceeds90%. Therefore, it’s significant to research the calculation and prevention of lightning induced overvoltage on distribution lines.In order to improve the safety and reliability of distribution lines and to provide valuable reference for lightning protection design, the mechanism and characteristic of natural lightning are introduced, six engineering calculation models about return-stroke current are compared and analyzed, and introduced the various models of characteristic, and determined the MTLE model with double exponential base current of a lightning current in this paper.Secondly, in the theoretical calculations of the electromagnetic fields around the lightning channel. By using Maxwell’s equations for the dipole current space radiation electromagnetic fields method are solved. Detailed derivation of the electromagnetic fields by lightning vertical discharge, differential equations regarding horizontal electric field Er, vertical electric field Ez and tangential magnetic field Hφ of any field point in lightning space are respectively derived. The horizontal electric field was calculated by using the Cooray-Rubinstein formula and in consideration of earth conductivity, and analysis of electromagnetic fields with a variety of factors.Then, the coupling model proposed by modified Agrawal model, and building distribution lines equations of lightning induced overvoltage, using of finite difference time domain (FDTD) method is derived induced overvoltage and current numerical iterative formula in the distribution lines. In addition, the lightning induced overvoltage on distribution lines characteristics were analyzed. Researched the lightning current amplitude, different high of overhead line, the horizontal distance of the line from the lightning point, ground conductivity and return stroke velocity factors which affect the lightning induced overvoltage. For an actual10kV overhead power distribution, calculated the lightning induced voltage, and obtained without considering the ground conductivity and take into account calculation results large difference, followed ground conductivity of increase the induced voltages decrease, and the influence of voltage characteristics.Finally, from the angle of reducing lightning induced overvoltage, analysis of the dangers of lightning overvoltage distribution lines, this thesis does research to reduce the effect of lightning induced overvoltage and improving lightning withstand level when arresters are installed. Proposed to improve the insulation level、installation scheme of stab-type arc-protection hardware and parallel protection gap etc. lightning protection measures, to ensure the lines security.