高压电缆绝缘热老化特性及破坏机理研究

Research on Insulation Thermal Aging Characteristic and Destruction Mechanism of High Voltage Cable

高压电缆长期运行过程中温度引起的绝缘材料热老化是影响其整体绝缘性能的重要因素。通过对高压电缆主绝缘层切片取样,研究分析了不同老化程度试样的微观形貌、官能团、结晶度、交联度等理化性能变化规律,测试分析了不同老化程度试样的电阻特性、介电性能和击穿特性,仿真模拟了不同温度下交联聚乙烯分子链的运动情况,进一步讨论了热老化对其微观结构的破坏演变机理。研究结果表明,老化2160 h后试样的晶区结构破坏较为严重,随着老化时间的延长,相邻晶区的间距增大,晶区排列松散,无定型区面积增大;羰基指数从3.88%增大至11.06%,羟基指数从1.58%增大至10.98%,结晶度从35.43%下降至35.05%,交联度先降低后升高。老化后试样的绝缘性能相应的发生变化,体积电阻率从2.76×10^(17)Ω·cm下降到4.10×10^(13)Ω·cm,介电常数从2.49增加至2.73,击穿场强从55.80 kV/mm下降到42.19 kV/mm,这主要是由于热老化破坏了试样的分子结构,促使其改变了结晶区与非晶区占比,产生了羰基、羟基等极性官能团,加快了电缆绝缘材料的性能下降。该工作对于高压电缆绝缘性能评价和异常分析具有指导意义。

Thermal aging of insulation materials caused by the temperature during long-term operation of high voltage cables is an important factor affecting their overall insulation performance.To investigate this,the physical and chemical properties as microscopic morphology,functional groups,crystalline and cross-linking degree of specimens of the main insulation layer of high voltage cables were studied by slicing and sampling specimens with different aging degrees.The resistance characteristic,dielectric properties and breakdown characteristics of specimens with different aging levels are tested and analyzed.The motion of cross-linked polyethylene molecular chains at different temperatures is simulated,and the mechanism of thermal aging damage to the micro-structure is further discusses.The research results show that the damage of the crystalline zone structure of the specimen is more serious after aging for 2160 h.With an extension of the aging time,the spacing of adjacent crystalline zones increased,the crystalline zones are arranged loosely,and the area of amorphous zone increases.The carbonyl index increases from 3.88%to 11.06%,the hydroxyl index increases from 1.58%to 10.98%,the crystallinity decreases from 35.43%to 35.05%,and the cross-linking degree initially decreases and then increases.The insulation properties of the specimens varies accordingly after aging.The volume resistivity decreases from 2.76×10^(17)Ω·cm to 4.10×10^(13)Ω·cm,the dielectric constant increases from 2.49 to 2.73,and the breakdown field strength decreases from 55.80 kV/mm to 42.19 kV/mm.It is mainly due to the fact that the molecular structure of the specimens is damaged due to thermal aging,prompting it to change the ratio of crystalline to amorphous regions,generating polar functional groups such as carbonyl and hydroxyl groups,and accelerating the property reduction of cable insulation material.This work is of guiding significance for the evaluation and abnormal analysis of insulation performance of high voltage cables.