基于热焓分析的变压器油热解机制及热故障严重程度评估

Thermal Decomposition Mechanism of the Insulation Oil Based on Enthalpy Analysis and Severity Evaluation of Transformer Thermal Faults

油中溶解气体总含量及其产气速率被普遍应用于诊断变压器内部故障的严重程度,但这类方法忽视了生成不同气体成分的能量差异。引入热焓分析研究了变压器油的热解机制与热故障严重程度的评估方法。基于热力学理论,对C20H42的热解产气机制进行了模拟,获得了不同气体组分的生成含量与温度的关系;然后依据热焓分析,对可表征反应过程能量变化的特征气体生成能进行了计算,得到各气体生成能的排列顺序为CH4<C2H6<C3H8<C3H6<C2H4<H2<C2H2;由此进一步建立了基于能量加权的油中溶解气体总含量分析法,提出评估变压器热故障严重程度的新判据。实例表明,与传统的油中溶解气体分析相比,基于能量加权的热故障严重程度评估方法具有更加准确、灵敏的应用优势。

The prevailing methodology used to identify the severity of transformer inner faults is based on the total gas concentration and its rate of change, without recurring to the energy of formation difference between gases. By means of enthalpy analysis, the thermal decomposition mechanism and thermal fault severity diagnosis criterion of transformer oil were studied in this paper. Based on the thermodynamic theory, C20H42 was selected as a model compound to study the decomposition mechanism of transformer oil, and the amount of individual gas with regard to different temperature was calculated. The energy of formation for each gas that can characterize the energy change during the reaction process was obtained, indicating the energy required to form the gases was in the order of： CH4 C2H6 C3H8 C3H6 C2H4 H2 C2H2. Futhermorre, an energy-weighted total dissolved gas analysis scheme was proposed, which formed a new criterion to evaluate the severity of transformer thermal faults. Field cases verification of thermal faults in transformer oil show that, compared with the traditional DGA method, the new proposed method renders preferable sensitivity and accuracy.