Analysis of the dynamics of changes in gas content in oil-filled equipment with defects of various types

Abstract

The article presents the results of analysing the dynamics of changes in the values of the ratios of characteristic gases, the percentage of gases, and defect nomograms in the process of developing electrical discharges, local overheating, and combined defects in high-voltage oil-filled equipment. During the analysis, the value of gas concentrations was evaluated for compliance with different levels regulated in the current Ukrainian standard at different stages of defect development. To determine the type of defect based on the values of the ratios of characteristic gases at different points in time, the norms regulated by the IEC 60599 standard and the ETRA square were used. The dynamics of changes in the percentage of gas was analysed using the Duval triangle. The results of the analysis showed that the primary defects during the development of electric discharges can be not only electric discharges with lower intensity, but also thermal (in particular, in the temperature range of 150-300 ℃) and combined defects. At the same time, in the process of discharge development, the nature of defects may change from measurement to measurement. Thus, when assessing the possibility of further operation of transformers, in addition to the degree of danger of the defect and the rate of its development, it is necessary to take into account the possibility of transforming the defect from a less to a more “dangerous” one that develops rapidly. During the development of thermal defects, the primary defect is usually a thermal defect with a lower hot spot temperature. It was found that in equipment with overheating above 700 ℃, the change in gas content during the development of the defect has a similar character. In particular, a mirror image of the change in the percentage of methane in relation to ethylene is observed. This effect can be used to detect high-temperature overheating at an early stage of its development, even before the gas concentrations exceed the limit values, which will help to avoid the destruction of equipment insulation and extend its service life. During the development of combined defects (overheating accompanied by discharges or discharges accompanied by heating), the main defect (e.g., discharge) first appears, and in the process of development, an additional defect (e.g., heating) develops. The results obtained indicate the possibility of detecting and recognizing defects in oil-filled equipment at different stages of their development.