高压电缆绝缘热老化特性及破坏机理研究

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 2 160 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 2.76×10¹⁷ Ω·cm to 4.10×10¹³ 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.