ANALYSIS OF THE DIAGNOSTIC CRITERIA USED TO DEFECT TYPE RECOGNITION BASED ON THE RESULTS OF ANALYSIS OF GASES DISSOLVED IN OIL

Abstract

Dissolved gas analysis is one of the most used and common diagnostic methods for high voltage oil-filled equipment. According to existing methods for interpreting the results of dissolved oil gas analysis, defect types are recognised using different diagnostic criteria. Using different methods to recognize the type of defect may result in different diagnoses. There are a sufficient number of publications on the comparative analysis of methods for the results interpretation of dissolved gas analysis. Most of them do not cover more than 4 methods at a time, and only a small number of publications deal with more methods. Some methods remain unreported, therefore an analysis of diagnostic criteria used in various standards and methods to identify types of defects by the dissolved gas analysis is given. The national standards of Ukraine and the Russian Federation, international methods, as well as a number of author's methods and standards are considered. All considered methods can be divided by the type of diagnosis, by the diagnostic criterion used and by the number of recognizable defects. According to the type of diagnosis, the considered methods can be divided into two groups – analytical and graphical methods. In the considered methods the following diagnostic criteria are used – values of gas concentrations or the gas pair ratios or gas percentage content. Most of the analysed methods allow identification of 6–7 most characteristic types of defects. The highest number of recognizable defects is 13–14, and the lowest only 3–4. Only a few methods make it possible to diagnose defect-free condition and/or damage of solid insulation as well as to recognize combined defects. The results show significant differences in the criteria and norms used by different standards and author's methods to determine the type of defect, which can lead to different diagnoses for the same data.