Clarification of Flashover Mechanism of Polymer Insulator

通过3个实验研究了聚合物绝缘子的闪络现象：(1)硅橡胶表面水滴(S)在交流电压作用下的行为；(2)表面条件对硅橡胶片局部放电特性的影响；(3)用盐雾法进行硅橡胶的加速试验。主要结果如下：1.硅橡胶上的水滴在施加电压高于阈值时开始振动。随着外加电压的进一步增加，液滴向电场方向延伸，最终通过桥联液滴发生闪络。闪络电压随水滴体积/数的增大而减小。高压电极附近的液滴似乎影响了闪络电压。在60 Hz电压作用下，观察到了18微升液滴的共振现象。电气绝缘能力可能会受到谐振的影响。在硅橡胶表面观察到有活性的局部放电，表面疏水性被人为地降低。与清洁雾相比，盐雾导致局部放电不那么活跃。这可能是由于硅橡胶上水滴周围的局部电场由于较高的盐雾电导率而被缓和。通过对加速试验后的样品进行化学分析，发现硅橡胶几乎没有降解。对于盐雾法硅橡胶棒的加速试验，电场应力为60V/mm，盐水电导率为800μS/cm，雾流量为0.6L/h较为适宜。

Flashover phenomenon of polymer insulator was investigated by carrying out the following three experiments : (1) behavior of water droplet(s) on silicone rubber under ac voltage application, (2) effect of surface condition on partial discharge characteristics of silicon rubber sheet and (3) acceleration test of silicone rubber by the salt fog method.The main results obtained are as follows :1. Water droplets on silicone rubber began to vibrate when the applied voltage was higher than a threshold value. With further increase in applied voltage, droplets were extended in the direction of electric field and finally flashover occurred by bridging droplets.2. Flashover voltage decreased when he volume/number of water droplet became larger. It seemed that a droplet near the high voltage electrode seemed to affect flashover voltage.3. Resonance phenomenon was observed for 18 micro-liter droplet under 60Hz voltage application. Electrical insulating capability may be affected by the resonance.4. Active partial discharges were observed on silicone rubber, where hydrophobisity of its surface was artificially reduced.5. Salt fog resulted in less active partial discharge compared with clean fog. This may be attributed to the fact that local electric field around water droplets on the silicone rubber is moderated due to higher conductivity of salt fag.6. Little degradation of silicon rubber was observed by chemical analysis of samples after the acceleration test.7. For acceleration test of silicone rubber rod by the salt fog method, electric stress of 60V/mm, conductivity of salt water of 800μs/cm and fog flow rate of 0.6 liter/h were seemed preferable.