基于非放射性氧同位素示踪法的SF6分解气体形成机理及放电模式识别的研究

Sulfur hexafluoride (SF6) is one of the most commonly used insulating mediums in high-voltage electrical equipment. Due to the poor manufacturing process, the residual particles and other internal defects, discharge faults show very high percentage in overall insulation faults. SF6 will decompose in the presence of water vapor and oxygen under electrical discharge, producing various gaseous by-products. Therefore, the SF6 decomposition method, i.e. analyzing the relationship between SF6 gaseous by-products and insulated faults, has been used as one of the most important criteria to diagnosis the insulation faults in recent years. It is shown that, for SF6 decomposition method, there is a big gap between experimental study and practical application. As a result, in this project, the Oxygen isotope tracer method is proposed as the key experimental tool, to trace back SF6 primary by-products and to analyze the oxidation mechanisms of SF6 in different electrical discharges, such as corona discharge, spark discharge and surface discharge, etc. Then, based on the trace of SF6 primary by-products under various discharge experimental conditions, the SF6 gaseous by-product formation mechanisms will be discussed. By finding the mapping between experimental macroscopic variables and microscopic variables, this project will establish the models of SF6 gaseous by-products where the unified microscopic physical quantities are regarded as the independent variables, to predict variations of SF6 gaseous by-products. Finally, according to the above study, the related rules and methods will be proposed to recognize the discharge patterns and to determine the severity of discharge faults, which can provide the theoretical basis and criterion for the discharge fault identification and online monitoring, to realize the purpose of fault diagnosis and early fault warning in SF6 insulated electrical equipment.

SF6分解气体法可通过检测SF6分解形成的特征气体及时发现内在潜伏性威胁并识别绝缘故障，得到了广泛关注。本项目利用非放射的氧18稳定同位素的标记物，通过氧同位素示踪实验，以半定量的方式探讨放电条件下SF6的氧化机理，建立可脱离实验环境的规整化放电模式识别的规则，为实际设备的在线监测和故障诊断提供理论依据和实用化判据。其中，在电晕放电、火花放电和沿面放电等故障的模拟中，采用微量注入含氧18同位素的水分或氧气的方法定量追溯SF6初级产物的积累和转化过程是重要的实验研究手段；宏观检测量与微观量的映射关系是剥离宏观实验条件的影响体现放电本质特征的关键；SF6分解气体的统一微观量建模是理解分解物在微观层面变化本源的必要条件；规整化放电模式识别规则和方法的确立是推动SF6气体分解法发展的根本，也是本项目的最终目的。

SF6 分解气体法可通过检测SF6 分解形成的特征气体及时发现内在潜伏性威胁并识别绝缘故障，得到了广泛关注。本项目利用非放射的氧18 稳定同位素的标记物，通过注入同位素水和氧气的方式，实施了电晕放电、火花放电和沿面放电等放电实验。利用氧同位素示踪法对比分析了三类放电下的分解产物及其特性，分析了主要气体分解物的含量、生成速率、比值等随施加电压、放电强度、微水和微氧等的变化规律；根据SF6的分解特征，推演了主要分解产物的形成机理。在实验结果的基础上，根据不同放电类型下特征分解产物的形成原因及其含量比值差异，提出了特征分解产物、特征对等模式识别指标，用以放电类型和放电强度等。结合模式识别和支持向量机理论，提取了含量比值(SOF2+SO2)/SO2F2、CO2/CF4和SO2F2/CO2和(SOF2+SO2)/CF4作为特征量，对电晕放电、火花放电、沿面放电以及放电强度等，进行了有效识别。本项目的主要研究成果有（1）提出了有别于以往文献的微水和微氧条件下SO2F2的生成机制；（2）提出放电程度的表征量，可表示电晕放电下辉光区电场的畸变程度；（3）提出了放电模式识别的分解气体特征对；（4）提出了分解气体的特征量组，可有效识别放电故障。此外，在实验与检测过程中，由于部分SF6重要分解气体无法用传统方法检测。为此，我们自主研发了用于检测SF6分解气体的光声光谱仪，与气相色谱-质谱技术联合，可检测多种特征分解气体，如SO2F2、SO2、SOF2、CS2、CO2、CO、CF4、H2S等；所研制的光声光谱仪，其SF6各分解气体的检测限均低于3μL/L，并获得中国计量科学研究院的检测证书。下一步拟与相关电力企业进行深入合作，开展检测仪器的示范应用和推广工作。