Diagnostics of Power Transformer Main Insulation According to the Oil Dielectric Strength Statistical Criterion

Abstract

Improvement of methods for assessing the technical condition of power transformers continues to be among urgent operation problems at power companies. A set of studies and calculations of the power transformer main insulation electrical strength has been carried out based on determining the transformer oil electrical strength statistical parameters with taking into account regulatory procedures and the newly developed method of statistical characteristics. The results obtained from calculations of the variation coefficient and the average breakdown voltage of operating oils for the transformers under study are considered and analyzed taking into account the requirements of regulatory documents in force in the power industry. An oil electric strength statistical criterion is determined based on the standard and by the method of statistical characteristics using the Gnedenko–Weibull distribution. A dependence of the oil electric strength statistical criterion limiting values on the power transformer power is obtained. An approach to diagnosing the power transformers’ main insulation electrical strength according to the oil electrical strength statistical criterion is proposed. The distribution histograms of the oil electrical strength statistical criterion and the oil breakdown voltages lower limit are shown. A positive correlation has been established between the oil electric strength statistical criterion and the variation coefficient based on a comparison of the statistical parameters obtained using the conventional diagnostic method and the one proposed in the ongoing study. The values of the operational transformer oil electrical strength statistical criterion for operating transformers are compared with the calculated limit values of this parameter. It has been found from the study results that with decreasing the electrical strength margin, the number of transformers that meet the electrical strength statistical criterion requirements decreases for all values of the transformer nominal capacity.