Clarification of Flashover Mechanism of Polymer Insulator

通过三个实验研究了聚合物绝缘子的闪络现象：(1)交流电压作用下水滴在硅橡胶上的行为；(2)表面条件对硅橡胶片局部放电特性的影响；(3)盐雾法硅橡胶加速试验。主要研究结果如下：1。当施加的电压高于阈值时，硅橡胶上的水滴开始振动。随着外加电压的进一步增大，液滴沿电场方向扩展，最终通过桥接液滴发生闪络。随着水滴体积/数量的增大，闪络电压降低。高压电极附近的液滴似乎会影响闪络电压。在60Hz电压下，对18微升液滴观察到共振现象。电绝缘性能可能受到谐振的影响。在硅橡胶上观察到主动局部放电，其中其表面的疏水性被人为降低。与洁净雾相比，盐雾产生的局部放电较少。这可能是由于硅橡胶上水滴周围的局部电场由于盐袋的高导电性而被缓和。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。采用盐雾法对硅橡胶棒进行加速试验时，优选电应力为60V/mm，盐水电导率为800μs/cm，雾流量为0.6 l /h。

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.