| In the vulnerable section of distribution line in strong minefield,it has little effect to improve the lightning resistance level and reduce the lightning trip rate by using existing lightning protection methods,but the lightning protection effect is outstanding by installing lightning protection wires on distribution lines.However,the installation of grounding line in distribution grid is not common enough,and there is a lack of experience in actual installation.How to install grounding lines safely and effectively in distribution lines is an urgent problem to be studied.Therefore,it is necessary to draw lessons from the structural erection method of grounding line in transmission grid,according to the typical climatic factors and the characteristics of lightning accidents in strong minefields,and around the three major parts of lightning protection performance,electrical safety and mechanical safety of grounding line installed on distribution lines,aiming at improving lightning protection performance,electrical safety and mechanical safety through a variety of combinations of erection modes,and ultimately gaining benefits after various constraints.The structural design requirements of grounding line installation are obtained by comparative analysis.Specific research contents are as follows:(1)The influence of lightning protection wire erection mode on lightning protection performance.The model of lightning distribution line and the mathematical model of lightning trip rate are established.By changing the horizontal position and erection height of grounding line with different spacing,the lightning resistance level and lightning trip rate of shielding and counterattack lightning strike types are calculated respectively.(2)Electrical safety performance analysis of grounding line installation.According to rated power frequency and lightning impulse,the finite element electric field model of grounding line-conductor is built.By changing the horizontal position and erection height of grounding lines with different spacing,the distribution of electric field strength between grounding lines and conductors is obtained.(3)Mechanical safety performance analysis of grounding line installation.Finite element simulation of grounding line structure field is carried out,and the sag and stress distribution of different types of grounding line,different spacing and different manufacturing line lengths are calculated.A total of 336 groups of simulation results are obtained.According to the above situation,the mechanical properties are compared and analyzed,and the effects of icing and wind pressure load on grounding line erection are studied.Finally,the finite element simulation of line structure field after adding grounding line is carried out.(4)Analysis of the influence of grounding line on the safety of distribution lines under typhoon disaster conditions.Finally,the damage calculation model of distribution line is established by dividing the geographic information grid,establishing the intensity-stress interference model including the design and the probability density function of actual wind load.The damage rate of distribution line before and after installing grounding line is calculated and analyzed,and the influence of the height of grounding line,the selection of grounding line and the spacing of grounding line on the damage rate of distribution line under typhoon disaster is studied.The main conclusions are as follows:(1)The conclusion of lightning protection performance analysis is as follows:(1)By designing suitable space position of lightning protection wire,the lightning protection level can reach 17~19 kA,and the lightning trip rate can be reduced to 3.7628-4.8519 times/(100 km per year);(2)The smaller the spacing,the better the lightning protection performance;From the point of view of lightning protection performance,the lower the height of grounding line,the closer the horizontal position to the center of cement pole,the better lightning protection performance.(2)Electrical safety performance analysis conclusion:(1)Under rated power frequency condition,the electric field strength distribution between grounding line and conductor is small,with specific values ranging from several kV/m to tens of kV/m.The insulation performance of the line is good,and it is not easy to occur inter-phase flashover.Under the lightning impulse condition,the electric field strength between the grounding line and the conductor is very large,ranging from 1000 to 8000 kV/m;(2)The higher the grounding line is erected,the better the electrical safety performance;The closer the grounding line is to the center of the cement pole,the better the electrical safety performance.(3)The conclusion of mechanical safety performance analysis is as follows:(1)The mechanical safety performance of grounding line LBGJ-55-27 AC is better than that of grounding line GJ-35 and GJ-50;If the thickness of icing is thicker and the wind speed is bigger,the sag and the minimum stress will be bigger;(3)In this chapter,the optimal erection schemes of three kinds of grounding lines with different spacing are obtained.(4)The calculation conclusion of damage rate of typhoon disaster is as follows:(1)The damage rate of distribution line increases from 0.00066~0.081 to 0.04~0.82 after adding grounding line under typhoon disaster;The span of tower,the height of grounding line and the type of grounding line will affect the damage rate of typhoon disaster line.Among them,the damage rate is obviously affected by the span;If the span is longer,the height of the grounding line is higher,the damage rate of the line is bigger;(4)If the LBGJ-55-27 AC grounding line is installed,the damage rate of the line is bigger than that of the other two grounding lines.The innovations are as follows:(1)For the lightning protection performance,electrical safety performance,mechanical safety performance and line damage rate under typhoon disaster,the structural design requirements of grounding line for distribution lines are obtained after comprehensive constraints of various parts,which has the optimum and comprehensive characteristics.(2)In view of the lightning protection performance of distribution lines after adding grounding lines,the calculation models of lightning protection level and lightning trip rate are established,and lightning protection level and lightning trip rate of different space locations of grounding lines under different spacing conditions are analyzed.Through comparison,the principles of grounding line installation that meet the requirements of lightning protection of distribution lines are obtained.(3)The damage rate calculation model of distribution line is established,which is divided into information gridding including geographic,electrical and meteorological information and intensity-stress interference model including probability density function of design and actual wind load.The damage rate of distribution line before and after installing lightning arrester is calculated and analyzed,and the influence of the height of lightning arrester,the selection of lightning arrester and the spacing of lightning arrester on the damage rate of distribution line under typhoon disaster is studied. |
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