触发闪电产生的地网地电位抬升及暂态效应

Ground Potential Rise and Transient Response of the Grounding Grid Based on the Triggered Lightning

对2019年夏季广州市从化区3个雷暴过程中7次触发闪电过程的39次继后回击和10次M分量及其对应的地电位抬升(ground potential rise,GPR)电压数据进行统计分析.分析发现:39次继后回击对应的地电位抬升电压峰值几何平均值能达到-138.97 kV,且波形具有明显的次峰,次峰几何平均值为-90.09 kV,约为最大峰值的64.86%;继后回击引起的地电位抬升电压主要由雷电流泄放引起(相关系数为0.94),感应耦合作用相对较弱(相关系数为0.55),而M分量过程对应的地电位抬升电压则均由雷电流泄放引起(相关系数为0.99).在雷电流瞬间冲击下,继后回击和M分量过程时的冲击接地电阻均小于工频接地电阻,M分量过程的冲击接地电阻平均值为12.02Ω,继后回击过程为10.87Ω.M分量半峰宽度可达毫秒量级,会使浪涌保护器长时间处于动作状态,极易引起浪涌保护器热崩溃损坏.

It is extremely dangerous of ground grid potentials which significantly rise when the lightning currents are flowing through the grid.A statistical analysis on 39 return-strokes,10 M-components and the ground potential rise(GPR)caused by them based on 7 triggered lightnings is carried out.According to the analysis,the geometric mean(GM)of the current peak values of 39 return-strokes is-12.78 kA,and the corresponding GM of GPR reaches-138.97 kV;the GM of the current peak values of the M-components is-0.60 kA,while the corresponding GM of GPR is-7.18 kV.There are distinct sub-peaks in the waveform of the GPR caused by the return-strokes,and the GM of the sub-peaks falls to-90.09 kV within several microseconds,about 64.86%of peak values.During the return stroke stage,the linear correlation coefficient of GPR voltages and the direct lightning current is 0.94,and the linear correlation coefficient of GPR voltages and the gradient is 0.55.It indicates that the GPR in return stroke stage is mainly caused by lightning current discharge in soil and the inductive coupling is relatively weaker.During the M-component stage,the correlation coefficient of peak value of GPR voltages and direct lightning current reaches 0.99,which means the GPR during M-component stage is mostly caused by lightning current discharge in soil.The impulse grounding resistance in the stage of return stroke when lightning current dispersing through grounding grids is 10.87Ω,and it is 12.02Ωin the stage of M-component.Both of the impulse grounding resistances are smaller than the DC grounding resistance,and the difference reaches 1.1 times.The minimum half-peak width of the GPR caused by the return-strokes is 0.44μs,of which the GM is 1.93μs,only 25.8%of the half-peak width of the corresponding current return-stroke.And the half-peak width of the GPR caused by M-components can be up to 2 microseconds,about 124 times of the GM of the half-peak width of the return-strokes,keeping the surge protective devices(SPD)running long which easily leads to crashing damages.