| As the main way of long-distance transmission,the safe and stable operation of EHV transmission line is closely related to the development of national economy.Because the corridor of EHV transmission line is very long,and the terrain is diverse,it is easy to be struck by lightning.CIGRE TB 549 indicates that 80%of ground lightning falls are multiple lightning strikes,and most of the negative ground lightning discharge channels are 3-5.When multiple lightning discharges,they will not strike at one point,and most of the lightning positions are linear distribution,when the lightning current strikes the line directly,it will produce a great Lightning Overvoltage on the line and equipment,causing the line trip fault,which poses a great threat to the security of power grid system and the reliability of power transmission.Therefore,it is necessary to study the electromagnetic transient effects caused by multiple lightning strikes on transmission lines,and compare and analyze the overvoltage effects caused by the first lightning strike and the subsequent lightning strike,so as to provide a theoretical basis for the protection of transmission lines caused by multiple lightning strikes.Firstly,the paper describes the discharge mechanism and various parameters statistics of multiple lightning strokes,and introduces the calculation methods of counterattack and shielding lightning withstand performance.Taking the 500kV Double Circuit Transmission Line on the same tower as the main research object,a complete simulation model is built by using atp-emtp.In this model,the multi wave impedance tower model which is more similar to the actual effect,the insulator flashover model which is based on the intersection method and the J.Marit line model which is based on the models programming module and the RC network to calculate the frequency varying parameter line are adopted,and the suitable lightning current models of the first lightning and subsequent lightning are established.Secondly,through the simulation model,the impact of power frequency voltage phase angle on the lightning withstand level of transmission line,the impact of counterattack overvoltage caused by the first lightning strike and subsequent lightning strike on the overvoltage of 500 kV double circuit transmission line on the same tower are calculated,and the changes of electromagnetic transient response of transmission line under different grounding modes of lightning conductor are considered.Based on the improved electrical geometry model,the shielding lightning overvoltage caused by multiple lightning strikes on 500 kV double circuit transmission lines on the same tower is calculated and analyzed.The research results show that the phase angle of power frequency voltage has a great influence on the lightning withstand level of 500kV transmission line,and the lightning withstand level of the line is the highest when the phase angle is 0°.The transient response of multiple lightning stroke lines varies greatly when different grounding methods are adopted.When the lightning wire is grounded tower by tower,the overvoltage caused by the first lightning stroke on both ends of the line and insulator is only 67.4%and 41.2%of that caused by the two ends grounding method,and the overvoltage caused by the subsequent lightning stroke on the line is only 57.2%of that caused by the two ends grounding method.Therefore,the electromagnetic effect of multiple lightning strokes can be greatly reduced by using grounding by base.When lightning strikes the center of the transmission line span,the lightning overvoltage caused by the first lightning and subsequent lightning will cause the single-phase insulator flashover failure and cause the line to trip.By reducing the protection angle of lightning line,reducing the tower height and reducing the ground inclination,the shielding lightning trip rate can be reduced.This result can provide a reference for the construction of line lightning protection. |
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