Lightning Damage Risk Assessment Of 220kV Transmission Line And Research On Impact Resistance Reduction Of Tower Grounding Device

Lightning strike is an important factor causing tripping of 220kV transmission lines,which threatens the reliable operation of the power grid.Different transmission line corridors have different lightning activity intensity,topography,geological structure,line lightning protection level,and load.Therefore,it is an important measure to improve the lightning resistance level and reduce the lightning trip rate to carry out the lightning risk assessment of the transmission line and carry out a reasonable lightning protection design according to the lightning risk level.In this paper,the AHP is used to construct the line lightning damage risk as the target layer element,the lightning trip rate,the average transmission equipment loss of the line,the average unplanned outage time,and the average economic loss of the outage time as the criterion layer elements.Lightning protection operation data is a three-layer hierarchical structure model of scheme layer elements.Calculate the weight of the lightning protection operation data of each line in the total,form a weight matrix with 5 rows and 4 columns,and use the combination of subjective and objective AHP-entropy weight combination method to calculate the weight of each index in the criterion layer for the line lightning risk.vector,which is multiplied by the resulting weight matrix to obtain the lightning risk of the transmission line under study.The obtained line risk ranking results are compared with the results obtained by using AHP and entropy weight method to determine the weight with the lightning tripping rate as an index,which verifies the rationality of the evaluation method in this paper.The lightning resistance level is an important characterization of the lightning protection capability of a transmission line.In this paper,a lightning-strike double-circuit transmission line tower model is established in PSCAD.The grounding resistance is simulated by a time-varying grounding resistance model that considers the spark effect when the inrush current enters the ground.The influence of power frequency voltage phase,dielectric strength and installation of lightning arrester on lightning resistance level at the moment of lightning strike is analyzed,and the difference between time-varying grounding resistance and power frequency grounding resistance on ground potential rise,tower top potential and lightning resistance level when lightning strikes a tower is emphatically studied.It is found that the lightning resistance level decreases sharply with the increase of the grounding resistance,and the time-varying grounding resistance model of the tower grounding resistance has a higher lightning resistance level.Then,the finite element method is used to establish the calculation model of the impact grounding resistance to simulate the ionization and spark effects of the soil,and the simulation is carried out in the finite element software COMSOL Multiphysics to analyze the resistance reduction mechanism of adding needle-punched short conductors to the horizontal grounding device and rationally arrange the needles.Need for thorns.The influence of the length,number,angle and position of acupuncture on the impact resistance reduction effect was studied,and it was found that the grounding resistance value decreased approximately linearly with the increase of the length of the acupuncture.The efficiency is getting lower and lower.When adding a single acupuncture,the way of unilateral vertical placement is the largest dispersion space,and the resistance reduction effect is the best.