The findings of the analysis of data on the accident rate of power transformers indicate that one of the main causes of their failures is a decrease in the dielectric strength of the insulation. To reduce failures and extend the service life of power transformers in operation, the issue of enhancing the techniques for assessing the condition of their internal insulation becomes relevant. Currently, when selecting the major insulation of transformers, one takes into account the dependency of the dielectric strength of the oil passage on its width. Experts discuss the issues involved in the choice of major insulation while taking into account the effect of the generalized factor being the volume of the oil passage. The solution to that problem largely depends on the study of the statistical characteristics of the dielectric strength of oil passages of different volumes and the effect rated parameters of transformers have on them. The efficiency of the application of such diagnostic characteristics depends on the extent of studies available on them and the establishment of their standardized parameters. The paper proposes a method for estimating the change in the transformer oil volume in stressed oil passages of major insulation of high-voltage power transformers and statistical characteristics of the dielectric strength of these passages while taking into account the effect of the rated values of capacity and voltage of transformers. It is shown that the degree of effect of transformer technical parameters on the statistical characteristics of the dielectric strength of oil passages depends on the quality of transformer oil, which undergoes a change in operating conditions.

The article presents a model for assessing the risk of op- erational failure of captive power plant units at oil and gas enterprises, taking into account the technical condition index (TCI). The model is based on the two-parameter Weibull distribution and the linear law describing the temporal evolution of the TCI. Risk is defi ned as the product of the probability of failure and the expected value of dam- age. Dependencies of the operational failure risk and the economic feasibility index of technical interventions on the TCI are obtained, enabling justifi cation of optimal threshold values of the TCI at which maintenance and repair actions are considered appropriate, taking into account the actual operating conditions of captive power plant units in industrial enterprises. The obtained dependencies are shown to be robust to variations in the model parameters.

The report presents the results of evaluating the effect of mechanical impurities on the electrical strength of transformer oil and discusses ways to reduce the risk of power transformer failures due to this factor.