Characteristics and Simulation of Artificially Triggered Lightning Precursor Current Pulse
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摘要: 2010—2014年夏季广州野外雷电试验基地采用了两种引雷火箭开展人工引雷试验,通过对25次经典人工触发闪电电流资料的分析,进一步证实了当火箭携带铜线时先驱电流脉冲 (precursor current pulse) 为双极性振荡型,火箭携带钢丝时先驱电流脉冲为单极性,其中单极性脉冲电流峰值、10%~90%上升时间、波形宽度和转移电荷量的几何平均值分别为26 A,0.33 μs,2.3 μs,27 μC,双极性脉冲相应的波形参数几何平均值分别为67 A,0.24 μs,2.1 μs,54 μC。双极性脉冲电流峰值的几何平均值接近是单极性的2.6倍,而波形持续时间和上升时间的几何平均值与单极性相近。利用传输线模型,模拟铜线通道底部电流波形呈双极性振荡型,而钢丝通道底部电流波形呈单极性,这与实际测量的结果比较一致,推测这两种电流波形可能是传输线特性阻抗不同所导致,在传输线顶端由先导起始放电产生的电流脉冲应为单极性。Abstract: During summers from 2010 to 2014, two kinds of rocket are used for artificially triggered lightning experiments in Guangzhou Field Experiment Site for Lightning Research and Testing. Based on the analysis upon current data of 25 classical rocket-and-wire triggered lightings, it can be confirmed that the unipolar precursor pulse is generated from the lightning triggered by copper wire, while the unipolar precursor pulse is generated from the lightning triggered by steel wire. As for the unipolar precursor pulse, the geometric mean (GM) values of peak current, rise time, duration of waveform and charge transfer are 26 A, 0.33 μs, 2.3 μs and 27 μC, respectively. While for the bipolar precursor pulse, the corresponding values are 67 A, 0.24 μs, 2.1 μs and 54 μC, respectively. The GM value of peak current for bipolar precursor pulse is close to 2.6 times that of the unipolar precursor pulse, however, GM values of duration and rise time are similar. Furthermore, the channel base current waveforms generated from copper and steel line are simulated by using the transmission line model. The simulated waveform is consistent with the observed one. The channel base current waveforms exhibit a bipolar oscillation, which can be caused by the obviously small characteristic impedance for copper wire than the grounding block. It is confirmed that the two forms of current waveform are caused by the difference between characteristics impedance of transmission line and grounding system. Precursor pulses are known that can be attributed to the superposition between the channel top current pulses and the bottom reflected current pulses. The current flows into the grounding system. If the characteristic impedance of transmission line doesn't match with the characteristic impedance of grounding system, the current will reflect at the connecting point between the transmission line and grounding system. With larger difference between the characteristic impedance of transmission line and grounding system, the reflection is more obvious. As a contrast, the characteristic impedance of steel wire is close to that of grounding system, which leads to weak reflection. Therefore, the current at the channel bottom generated from triggered lightning with steel wire is the same as the top current. The current pulses generated by the upward leader initial discharge at the top of the transmission line are unipolar. The conclusion is also verified by simulation results.
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表 1 人工触发闪电单极性先驱电流脉冲波形参数统计
Table 1 Unipolar precursor current pulse waveform parameters of the artificial triggered lightning
单极性脉冲 Ip/A T10/μs S10/(kA·μs-1) TW/μs Q/μC THPW/μs 算术平均值 28 0.39 0.08 2.4 30 0.81 几何平均值 26 0.33 0.06 2.3 27 0.73 标准偏差 13 0.25 0.07 0.7 12 0.38 最大值 131 1.75 0.64 4.7 69 3.12 最小值 13 0.08 0.01 1.0 8 0.16 中值 24 0.32 0.06 2.4 29 0.75 表 2 人工触发闪电双极性先驱电流脉冲波形参数统计
Table 2 Bipolar precursor current pulse waveform parameters of the artificial triggered lightning
双极性脉冲 Ip/A T10/μs S10/(kA·μs-1) TW/μs Q/μC THPW/μs 算术平均值 78 0.28 0.55 2.2 73 0.88 几何平均值 67 0.24 0.25 2.1 54 0.70 标准偏差 43 0.22 0.35 0.7 66 0.63 最大值 201 1.28 1.68 5.4 302 2.35 最小值 22 0.07 0.02 0.8 13 0.15 中值 71 0.17 0.30 2.4 52 0.64 表 3 模拟数值结果
Table 3 Simulated numerical results
模拟结果 初始电流 铜线 钢丝 测量结果 模拟结果 测量结果 模拟结果 电流峰值/A 28 69 68 25 26 波形持续时间/μs 2.8 1.8 1.6 2.1 2.6 10%~90%上升时间/μs 0.2 0.18 0.21 0.19 0.2 -
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