Clarification of Flashover Mechanism of Polymer Insulator

本文通过三个实验研究了硅橡胶表面水滴在交流电压下的闪络行为、表面条件对硅橡胶片局部放电特性的影响以及盐雾法加速硅橡胶片的闪络特性，主要结果如下：1.当外加电压高于阈值时，硅橡胶表面的水滴开始振动。随着外加电压的进一步增加，液滴沿电场方向扩展，最终通过液滴桥接发生闪络.闪络电压随水滴体积/数量的增大而降低。高压电极附近的液滴似乎会影响闪络电压。在60 Hz电压作用下，18微升液滴出现共振现象。电绝缘能力可能会受到谐振的影响。人工降低硅橡胶表面疏水性后，在硅橡胶表面观察到主动局部放电.盐雾导致较少的主动局部放电相比，干净的雾。这可能是由于盐雾具有较高的电导率，使硅橡胶表面水滴周围的局部电场减弱。通过加速试验后样品的化学分析，观察到硅橡胶的降解很少.盐雾法加速硅橡胶棒的电应力为60 V/mm，盐水电导率为800μs/cm，雾流量为0.6L/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.