高压开关柜阻燃绝缘件在役老化诱发着火事故的综合分析

高压开关柜长期连续运行在高温高湿环境下,内部的阻燃绝缘件会老化而导致性能劣化,进而引起电弧击穿乃至着火事故。为揭示绝缘件样品老化对其击穿与引燃特性的影响机制,针对已在役运行12年开关柜内老化阻燃固封极柱样品和同配方新样品,开展了微观形貌、热重-差示扫描量热、热重-红外光谱和微量燃烧特性综合分析。结果表明:开关柜内的长期电热应力易使环氧树脂绝缘材料的微观结构产生破坏,内部易产生孔洞和裂纹,导致其绝缘性能下降;开关柜内的高温环境易使绝缘材料内部分子链缓慢断裂,导致老化样品更易受热分解;同时,柜内高温高湿环境既可使其材料内部孔隙吸湿而降低绝缘性能,还易导致磷系阻燃剂吸潮氧化,降低其阻燃性能;最后,与新样品相比,12年老化样品在升温初期的燃烧释热更高,一旦形成击穿电弧,更易着火燃烧。研究结果为高压开关柜因绝缘件老化失效而形成击穿起火事故提供了分析要点,并可作为未来更高性能阻燃绝缘件的优化设计依据。

Analysis of fire accidents induced by in-service aging of flame-retardant insulation items in high-voltage switchgear

The high-temperature and high-humidity environment in high-voltage switchgears, which usually continuously work for a long time, is likely to cause aging and deterioration of flame-retardant insulation items in them. In this case, arc breakdown and even a fire accident might happen. To reveal the influence mechanism of the aging of the insulation samples on its breakdown and ignition characteristics, the scanning electron microscope (SEM), thermal decomposition analysis (TG-DSC, TG-FTIR), and micro-scale combustion calorimetry (MCC) experiments were carried out for the 12-year-old flame-retardant embedded pole samples in the switchgear and the new samples with the same formula. The results show that the long-term electrical and thermal stress in the switchgear is likely to cause apparent damage to the structure of the epoxy resin insulation material. Holes and cracks will be generated in the material, which causes a decrease in its insulation performance. It also suggests that the high-temperature environment in the switch cabinet will cause the break of inner molecular chains of the material, which makes the aged samples more susceptible to thermal decomposition. In addition, the high-temperature and high-humidity environment in the cabinet can not only make the internal pores of the material absorb moisture and reduce the insulation performance, but also easily cause the phosphorus-based flame retardant to absorb moisture and oxidize, reducing its flame retardant performance. Finally, compared with the new sample, the 12-year-old sample has a higher combustion heat release in the initial heating stage. Therefore, it is easier to be ignited and starts burning by heating the arcing. The results provide the critical points for the breakdown and fire accidents of high-voltage switchgear due to the aging and failure of insulating parts. It can also be helpful for the optimal design of higher-performance flame-retardant insulating parts in the future.