水平分层大地电导率对倾斜通道LEMP 场影响研究

为了得到水平分层条件下,放电通道倾斜角度、大地电导率以及分层土壤厚度对倾斜通道雷电电磁脉冲(LEMP)场的影响规律,在差分条件下对三维直角坐标系的倾斜放电通道加源方程进行了推导,在此基础上利用时域有限差分(FDTD)法对倾斜通道雷电电磁场进行了建模。研究结果表明,当放电通道倾斜角度改变时,雷电电磁场峰值会随着倾斜角度的增加而出现明显的上升,同时观测点与雷击点之间的距离越大倾斜角度对电磁场的影响越明显。当电导率发生改变时,上层电导率主要影响电磁场的峰值,而底层土壤电导率主要影响电磁场的下降沿陡度和波尾幅值,对电磁场峰值影响较小,基本可以忽略。此外,电场波形的下降沿陡度随土壤上层电导率的减小而增加,随下层电导率的减小而降低。当上层土壤厚度改变时,在影响深度范围内电场波尾幅值会随着上层厚度的增加而增加,但电磁场峰值基本不受影响,而且随着水平距离的增加表层土壤的影响深度在不断加大。

The Influence of Horizontal Layered Ground Conductivity on Oblique Discharge Channel LEMP EM Fields

In order to get the influence of tilt angle, horizontal layered ground conductivity and layered soil thickness on oblique channel lightning EM pulse (LEMP) fields, the current source equations of oblique channel lightning EM fields are derived under conditions of finite difference. After that the finite-difference time-domain (FDTD) method was used in 3-D Cartesian coordinate system to calculate EM fields generated by oblique discharge channel. The results show that, the peak value of EM fields will increase with the increasing of the tilt angle, moreover, the impact of tilt angle on EM fields will be more greater with the increasing of the distance. When ground conductivity changes, the upper layer ground conductivity mainly affects the peak of EM field and the lower layer ground conductivity mainly influences the falling edge steepness and the wave tail amplitude of EM fields. Apart from that, the falling edge steepness of electric fields will increase with the decrease of the upper layer ground conductivity and decrease with the decrease of the lower layer ground conductivity. When the upper layer thickness changes, it has little effect on the peak of EM field, but the wave tail amplitude of electric field will increase with the increase of the upper layer thickness. Moreover, with the increase of horizontal distance the sphere of influence of upper layer ground thickness will be expanded.