一次触发闪电地电位抬升引发的氧化锌电涌保护器损坏事件分析

ANALYSIS OF ZnO SURGE PROTECTIVE DEVICE DAMAGE CAUSED BY GROUND POTENTIAL RISE IN ONE TRIGGERED LIGHTNING FLASH

关键词:  人工触发闪电  地电位抬升  残压  流经SPD电流  氧化锌电涌保护器  损坏

Key words:  artificially triggered lightning  ground potential rise  residual voltage  current flowing through SPD  ZnO surge protective device  damage

摘要:

基于触发闪电开展了电流注入地网后地电位抬升反击氧化锌电涌保护器的试验研究。结合真实雷电环境下测量的电涌保护器两端残压和流经电流的数据，对一次触发闪电引发的氧化锌电涌保护器损坏事件进行了分析。分析发现，电流注入地网后，回击过程瞬间的大能量和长连续电流过程累积的能量相互叠加共同作用损坏了氧化锌电涌保护器。回击发生时，较大的地电位抬升反击特别是电压的快速上升阶段，氧化锌电涌保护器内部半导体结构(晶界层或晶粒)很容易遭到局部破坏，形成穿孔，电压波沿着破坏的晶界层“漏洞”迅速通过，氧化锌电阻片失去钳制作用，而当电压缓慢下降时，电压在氧化锌电涌保护器内部晶界层的分布趋于均匀，没有损坏的晶界结构又恢复了氧化锌电涌保护器的钳制功能。长连续电流过程形成的残压较小，但其持续时间很长，可达几十甚至上百毫秒，事件中多次致使SPD钳制功能的失效。4次回击过程地电位抬升反击流经氧化锌电涌保护器的电流峰值最大为7.1 kA，平均值5.4 kA，占触发闪电注入电流的28.9%。流经SPD的电量范围0.15～0.58 C，平均值0.44 C，其值大于8/20 μs标称放电电流20 kA单脉冲释放的电量(0.37 C)。

Abstract:

Based on triggered lightning, this paper carries out an experimental study on the counterattack of ground potential rise (GPR) to a surge protective device (SPD) after a current is injected into the grounding grid. Then, the paper analyzes the ZnO SPD damage event by considering the measured data of residual voltage at the two terminals of the SPD, as well as the current flowing through it in a real lightning environment. The analysis shows that, after the current is injected into the grounding grid, the ZnO SPD is damaged under the joint influence of mutually-superimposed instantaneous large energy in the return strokes and accumulated energy in the long continuous current process. When a return stroke occurs, due to the impulse of large GRP, particularly in the stage where the voltage rapidly rises, the semiconductor structure (grain boundary layer or grain) in the SPD is prone to partial damage, and holes are formed. After this, the voltage wave quickly passes through the “holes” along the damaged grain boundary layer and the ZnO resistor loses its clamping effect. When the voltage drops slowly, the distribution of voltages in the grain boundary layer of the SPD tends to be uniform, while the undamaged grain boundary structure enables the SPD to restore its clamping function. The residual voltage formed in the long continuous current process is small but lasts for a long period of time (tens or even hundreds of milliseconds). This disables the clamping function of the SPD for several times during the event. The maximum peak value of the current flowing through the SPD due to the GPR counterattack during the four return strokes is 7.1 kA, with a mean value of 5.4 kA, accounting for 28.9% of the injected current in the triggered lightning. The electrical quantity flowing through the SPD ranges from 0.15 to 0.58 C, with a mean value of 0.44 C, which is greater than that discharged from a single pulse of the nominal discharge current 8/20 μs of 20 kA (0.37 C).