XLPE电缆绝缘老化临界时间现象及其动力学仿真

Critical time phenomenon in ageing of XLPE cable insulation and the kinetics modeling

为深入探究交联聚乙烯(cross-linked polyethylene, XLPE)电缆绝缘的老化特性,评判XLPE电缆绝缘的老化程度,文中对110 kV XLPE电缆绝缘在135℃进行加速老化实验,采用拉伸试验表征XLPE断裂伸长率的变化规律,采用傅里叶变换红外光谱表征XLPE中羰基浓度与抗氧剂含量的变化规律。结果表明,XLPE电缆绝缘老化存在临界时间现象,即随着老化时间的增长,XLPE断裂伸长率由缓慢下降转变为快速下降,羰基浓度由缓慢增大转变为快速增大,临界时间均为2 016 h;而抗氧剂含量则随老化时间逐渐下降,不存在拐点。基于链式自由基理论,建立考虑抗氧剂反应过程的XLPE热老化动力学模型,进一步仿真计算XLPE电缆绝缘热老化过程中抗氧剂含量和羰基浓度的变化过程,仿真计算结果能够很好地吻合实验结果。研究结果表明抗氧剂含量可用于表征XLPE电缆绝缘的老化程度。

In order to comprehend the ageing characteristics profoundly and evaluate the ageing degree of cross-linked polyethylene(XLPE) cable insulation, the XLPE cable insulation is subjected to accelerated ageing experiment at 135oC. The variation of elongation at break is characterized by the tensile test. The carbonyl concentration and antioxidant contents in XLPE are measured by Fourier transform infrared spectroscopy. Results show that the ageing of XLPE cable insulation exhibits critical time characteristic, namely elongation at break of XLPE decreases slowly and then decreases dramatically with ageing time. Meanwhile the carbonyl concentrations also increase slowly at first and then increases rapidly. The critical time is 2 016 h when aged at 135oC. While the content of antioxidant gradually decreases without inflection point. Based on the chain free radical theory, the thermal ageing kinetics model considering the reaction of antioxidant is established, and the variation of antioxidant content and carbonyl concentration during the thermal ageing of XLPE cable insulation are furtherly calculated by simulation. Simulation results are in good agreement with the experimental results. The results indicate that the antioxidant content could reveal the ageing degree of XLPE insulation.