Research And Application Of Gas Chromatography Analysis Method For Trace Impurity Gas In SF₆

SF₆ gas insulated high-voltage equipment is widely used in the operation of the national power grid,where high concentration of SF₆ in the equipment has the functions of arc extinguishing and insulation,meanwhile the gas may gradually react with the SF₆-chamber materials under critical conditions in the long run,which can lead to invalidity of the equipment and even safety issue.Therefore,it is particularly important to detect latent faults in the equipment as early as possible.SF₆ breaks down into a variety of sulfides and fluorides under critical conditions,while these substances may further react with other equipment parts(polytetrafluoroethylene plastic insulator)or trace impurities(oxygen or water)to generate more substances,and the analysis regarding kinds and contents of the resultant substances can effectively assess the operating status of SF₆ high-voltage equipment.Apparently,it is crucial to develop reliable methods for analyzing other trace gases in SF₆.In this thesis,two gas chromatographic methods were developed for simultaneous determination of multiple fluorocarbon gases and multiple sulfur-containing gases,respectively.The developed methods have been applied to real samples.Based on the existing analytical methods,principal component analysis and cluster analysis were employed to carry out a correlation analysis between a variety of trace gases in SF₆ high-voltage equipment and the possible corresponding faults.This thesis consists of four chapters.Each chapter is summarized as follows:Chapter 1:IntroductionIn this chapter,the usual source,determination methods and significance of fluorocarbons,as well as sulfur-containing gases are introduced.Then,the types of gases produced when SF₆ high-voltage equipment faults/failures occur was briefed,classified and sorted out with the aim to get correlated with possible equipment faults/failures.To conclude,the significance and contents of this study was elucidated.Chapter 2:A GC-FID method for simultaneous determination of three fluorocarbon gases in bulk SF₆ studyWith the aim to solve the challenge of qualification and quatification of micro C₃F₈,C₄F₈ and C₄F₁₀ in bulk SF₆,a GC-FID method was developed with a separation core basing on HP-PLOT Al₂O₃ KCl chromatographic column,where not only three analytes were separated from bulk SF₆,but separated were the three analytes from each other.The analysis of each analyte is free from interference with one another.The developed method exhibits wide linear response from analytes of 2-400 ?L/L,good sensitivity and repeatability(RSD is less than 1%),and has been applied to the analysis of real gaseous sample in SF₆ high-voltage circuit breakers.This research provides a reliable tool for the diagnosis of latent fault in SF₆-related electrical equipment.Chapter 3:Study on a GC-SCD method for simultaneous determination of four sulfur-containing gasesSimultaneous determination of H₂S,COS,CS₂ and SO₂ constitues one of the important task of air quality control.As to the specific requirement of the task,based on elaborately choosing chromatographic column and optimizing the other chromatographic conditions,a GC-SCD method was developed.The developed method allows the complete separation of analytes with high sensitivity for detection,wide linear range and good repeatability.This method has been applied to real air sample with satisfactory results.Chapter 4:A PCA-CA method with a basis on a variety of trace gases and its application in tracing causes of SF₆ high-voltage equipment failureAiming at the challenges encountered when exploring the correlation between the multiple "messenger" gases in SF₆ high-voltage equipment failure and their corresponding fault types,a method for tracing the causes of SF₆ high-voltage equipment failure was developed via the principal component analysis and cluster analysis of the information of 13 trace "messenger" gases in a lot of faulty SF₆ high-voltage equipment.By taking the advantage of reflecting the natural chemistry in the scene with statistics,we can reduce the dimensions of the gas information,classify one and the same failure/fault and depict their characteristics.The study found that three principal components were extracted from 13 gases of a lot of faulty equipment,and the chemical characteristics of these three principal components were highly consistent with those of the condensed variables(H₂,CF4 and CO₂)in cluster analysis,and the failure/fault types can be classified into 5 categories,including inasieness type,ordinary carbon type,severe carbon type,medium type and mixed type.This study provides an efficient research approach for tracing the causes of a large number of SF₆ high-voltage equipment failures/faults.