热老化时间对硅橡胶电树枝起始特性的影响

Influence of Thermal Aging Time on Electrical Tree Initiation of Silicone Rubber

电缆系统长期运行在高温下会对新型超高压预制式电缆附件主绝缘材料硅橡胶(SIR)的性能产生影响。针对电缆长期最高运行温度(90℃)下热老化时间对硅橡胶材料电树枝老化特性的影响展开试验研究,测定90℃温度场下老化1 000 h对硅橡胶材料电树枝老化特性的影响规律,并进行理论分析。试验结果表明,90℃热老化作用下,硅橡胶随着老化时间的增加,起树电压出现先增再减的趋势。硅橡胶电树枝形态与老化时间密切相关,老化过程中树枝状比例很低,随着老化时间增加,丛状树枝比例先增再减,松状比例先减再增。另外,通过对最大放电量的测试可以发现,最大放电量的变化随时间先减再增。结合差热分析、平衡溶胀等试验对试验结果进行分析讨论后认为,90℃下硅橡胶交联网络破坏是硅橡胶起树电压大幅下降,电树枝形态改变的重要原因。运行温度下的热老化对硅橡胶的性能产生了严重的影响,需要引起重视。

Power cable operating at high temperature over a long period would influence the electrical performance of silicone rubber （SIR） in the new types of extra-high voltage prefabricated cable accessories. Through tests, we revealed the relationship between thermal aging time （0-1 000 h） at 90 ℃and the characteristics of electrical tree aging： the electrical tree initiation voltage increases and then decreases with time; the thermal aging time greatly affects the characteristics of electrical trees, for instance, as the thermal aging develops, the proportion of pine-like trees firstly de- creases and then increases, the proportion of bush-like trees firstly increases and then decreases, while the proportion of branch-like tree keeps low; the maximum discharge capacity firstly decreases and then increases with aging time. Further analysis combined with experiments of differential scanning calorimetry （DSC） and equilibrium swelling, it is concluded that the breakdown of cross-linking network in SIR causes all the changes mentioned above. Hence we should pay more attention to the thermal aging of SIR in operation.