TPEE与ETFE对绝缘油热老化特性影响分析

Effects of TPEE and ETFE on Thermal Ageing Characteristics of Insulating Oils

选择护套材料分别为热塑性聚酯弹性体(TPEE)和乙烯-四氟乙烯共聚物(ETFE)的两类特种光纤,在130℃绝缘油中进行加速热老化缩比试验,并对绝缘油的红外光谱、体积电阻率、介质损耗因数、微水含量、酸值进行测试。结合光纤护套的微观形貌变化,分析含纤油样的热老化特性变化规律。结果表明:在130℃油环境中两类特种分布式光纤均会加速绝缘油的老化,并对油样的热老化特征量产生整体性影响。TPEE对绝缘油的介质损耗因数(tanδ)影响大于ETFE,热老化24 d后含TPEE光纤油样与含ETFE光纤油样的tanδ分别为纯油样的4.5倍和2.7倍,而两类含纤油样的体积电阻率变化差距不明显。含纤油样的微水含量和酸值在热老化期间均呈指数增长。分析其原因为热应力作用下发生的热解和水解反应,同时光纤护套老化分解,其部分烃类物质的弱C-H、C-O键断裂,加快了高温条件下油样的热老化"正反馈"进程。通过油样的傅里叶红外光谱与护套的SEM图分析,认为光纤护套的不同程度分解是造成绝缘油热老化特性变化的直接原因。

Two kinds of optical fibers were selected for the small-scale experiment of accelerated thermal ageing in insulating oils at 130℃, of which the sheath materials were thermoplastic polyester elastomer （TPEE） and ethylene-tetrafluoroethylene copolymer（ETFE）, respectively. The infrared spectra, volume resistivity, dielectric loss factors, moisture contents, and acid values of the insulation oils were measured. Combined with the micro morphologies changes of sheathes, the variation of thermal ageing characteristics of the oils containing optical fibers were analyzed. The results show that two types of special distributed optical fiber accelerate the ageing of insulating oils at 130 ℃ and have overall effects on the thermal ageing characteristics of oil samples. TPEE has a greater influence on dielectric loss factor of insulating oil than that of ETFE. After thermal ageing for 24 days, the tanδ of TPEE fiber-containing oil and ETFE fiber-containing oil are 4.5 times and 2.7 times larger than tanδ of pure oil, respectively, while the difference of the volume resistivity changes of the two oils containing fibers are not obvious. The moisture contents and acid values of fiber-containing oils increase exponentially during thermal ageing process. The reasons are the pyrolysis and hydrolysis reactions under the effect of thermal stress. At the same time, the aged optical fiber sheaths decompose, and the weak bonds such as C-H and C-O in some hydrocarbons break, which accelerate the ＂positive feedback＂ process of thermal ageing of oil samples under high temperature. Furthermore, according to the analysis of infrared spectra of the oil samples and SEM photographs of the sheaths, it is thought that the varying degrees of decomposition of the optical fiber sheath is the direct cause for the changes of thermal ageing properties of insulating oil.