Analysis of the main problems arising during the recognition of the defect type based on the results of the dissolved gases analysis

Abstract

The article presents the results of the analysis of the main problems that arise when recognising the defect type in oil-filled equipment of electric power networks based on the results of the dissolved gases analysis. On the example of interpreting the actual results of the dissolved gases analysis, the main problems arising in the recognition of partial discharges, spark discharges, discharges with low and high energy density, local overheating and combined defects are analysed using the graphical method from the IEC 60599 standard, the ETRA square and the Duval triangle. The analysis revealed significant discrepancies in the norms and criteria regulated by different standards and methods for interpreting the results of the dissolved gases analysis to recognise the same defect. The research results showed that for almost all the analysed defects, the non-recognition is caused by the absence of normalised values of diagnostic criteria (values of gas ratios, percentage of gases and ratios of gas concentrations to the gas with the maximum content) for some defects or combinations of several defects. False diagnoses are made when identifying the type of defects in oil-filled equipment based on the results of the dissolved gases analysis because the values of individual gas ratios or percentage content of individual gases are not taken into account. The analysis revealed contradictions in the diagnoses made when different diagnostic criteria (ratios of characteristic gases and percentage of gases) are used for the same results of the analysis of gases dissolved in oil. Ensuring reliable recognition of the type of defect in oil-filled equipment based on the results of dissolved gas analysis is possible thanks to an integrated approach that includes not only the analysis of gas ratios, but also the analysis of the percentage of gases and defect nomograms. In addition, it is crucial to take into account the physicochemical laws of gas formation in oil, in particular, the dependence of gas content on the temperature or energy of defects.