Analysis of distribution laws of insulation indicators of high-voltage oil-fillled bushings of hermetic and non-hermetic execution

Abstract

The object of research is the distribution laws of capacitor-type insulation values that were obtained during preventive tests for both serviceable and defective high-voltage bushings of 110 kV of hermetic and non-hermetic execution. One of the most problematic areas is insufficient knowledge and lack of justification of the laws for distributing these preventive tests of insulation of bushings. In the course of the research, a comprehensive approach to the solution of the problems was used, including probability theory and statistical analysis, analysis of world experience and a logical approach. In the long term, the results are expected to be extended to the bushing of other types having similar problems in the diagnosis of the condition. The method of statistical processing of the results of periodic tests of high-voltage bushings is proposed, which allows to form arrays with homogeneous values of indicators in conditions of limited measurement information. It is established that for the bushings of hermetic and non-hermetic execution, the insulation values for both the serviceable and faulty state can be described by the Weibull distribution. It is established that the distribution densities for serviceable and faulty state of high-voltage bushings intersect, and therefore it is impossible to select the maximum permissible values of insulation parameters that would not give erroneous solutions. The maximum permissible values of the insulation indices of high-voltage oil-filled bushings are proposed using statistical methods and taking into account the most significant operational factors. It is shown that for high-voltage bushings of the same execution there is a shift in mathematical expectations, which is due to the difference in operating time and different load factors of transformers. This circumstance must be taken into account when adjusting the maximum permissible values of the insulation indices of high-voltage bushings. The use of the developed algorithms and procedures of mathematical statistics in the problems of diagnosing high-voltage bushings contribute to improving expert judgment and decision-making.