交联聚乙烯绝缘电缆老化的介电响应与局部放电特性研究

Dielectric Response and Partial Discharge Characteristics of XLPE Insulation Cable During Ageing Process

为研究交联聚乙烯(XLPE)电缆老化特性并探究影响材料介电性能的微观因素,对不同老化状态的XLPE电缆进行等温松弛电流与局部放电测试。构建纯聚乙烯分子P;、含羟基的老化聚乙烯分子P;以及进一步热氧老化的含羧基聚乙烯分子P;模型,并基于不同老化状态的聚乙烯分子开展量子化学计算。结果表明:随着老化时间的增加,去极化电流时间常数、老化因子A增大,且绝缘介质中的陷阱数量与能级深度增加,同时,老化电缆中出现幅值更大且数量更多的局部放电。聚乙烯分子链中因热氧老化所产生的碳氧基团是造成材料中陷阱数量增多与能级深度增加的重要原因,且官能团的种类会直接影响陷阱能级分布。在电场作用下,老化的聚乙烯分子链稳定性更差、偶极矩更大、电荷转移更为明显,造成老化电缆绝缘中的电荷更易入陷而聚集,从而造成局部电场集中,提升了电缆中的局部放电水平。

In order to study the ageing characteristics of cross-linked polyethylene(XLPE) cable and explore the microscopic factors affecting the dielectric properties of materials, the XLPE cables with different ageing states were conducted isothermal relaxation current(IRC) and partial discharge(PD) tests. A pure polyethylene molecular chain P;, an aged polyethylene molecular chain P;containing hydroxyl groups, and a further thermaloxidative aged polyethylene molecular chain P;containing carboxyl groups were established, and polyethylene molecules with different ageing states were carried out quantum chemical calculation. The results show that with the increase of ageing time, the time constant of depolarization current and ageing factor A increase, and the trap number and energy level depth in insulating medium increase. Besides, there are more partial discharges with higher magnitude occurring in the aged cable. The carbon-oxygen group generated by thermal oxygen ageing in polyethylene molecular chain is an important reason for the increase of trap number and energy level depth, and the type of functional group will affect the distribution of trap energy level directly. Under the effect of electric field, the stability of the aged polyethylene molecular chain becomes worse, the dipole moment is larger, and the charge transfer is more obvious, which make the charges in the aged cable insulation more likely to be trapped and accumulate, resulting in electric field concentration and increase of partial discharge level.