The Assessment Research Of The Aging Of Transformer Insulation Based On Actual Operating Conditions

Power transformers have not only been the important assets of power companies, but also become the core of the power transmission system. A safe and stable operation of power transformers is directly related to the safety of power grid and its reliable operation. The consequences of failure will be catastrophic, and the purchase and maintenance’s costs are high. Therefore the timely understanding of insulation condition of transformers is very necessary so as to provide decision-making information for the condition-based maintenance. Nonetheless, the current domestic transformer insulation aging assessment is in its infancy, it has yet formed a complete set of evaluation system. Fuzzy comprehensive evaluation of the evidence and evidential reasoning are two common transformer condition assessment methods, and the arithmetic characteristics of these two algorithms with transformer insulation aging characteristic coincide with the aging of transformer insulation (ambiguity and uncertainty). Currently, two methods based on transformer insulation aging assessment are at their initial stage, only the feasibility and effectiveness of the evaluation method are verified, thus the practical application of field guidance are lacked.The transformer solid, liquid insulation aging reasons have been analyzed in this paper. Combined with the constructive principles of the comprehensive evaluation system, and detailed analysis of the evaluation system of the indicators of the insulating effects of aging, the transformer state comprehensive evaluation system has been established. Then by confirmimg the factors sets of U, reviews sets of V, evaluation matrixs of R, the insulation fuzzy comprehensive evaluation of the transformer based on the aging state evaluation model has been established, in which the membership function in accordance with the semi-trapezoidal distribution and half ridge-shaped distribution combined distribution, establishing all membership function evaluation index. The views of four experts were taken in this paper with the purpose of giving a constant weight index by AHP method. Based on a formula based on variable weight equalization function, the actual index data values (normalized) weights for constant correction, a subjective and objective combination has then been achieved. Hence rendering the weight distribution to boast more practical significance. Since there have been failure problems in synthetic formula evidential reasoning, therefore the confidence factors were introduced. Nonetheless, to determine the confidence factors α1 has been highly subjectivive, thus another method has been introduced-the calculation method based on the confidence of the similarity matrix. Confidence factor α2 obtained by this method is entirely obtained from the evidence itself, so that the results gained by the two methods have a strong contrast. Finally, the insulation aging state based on evidence theory was introduced in the transformer evaluation process evenntually to construct the health of the index. Moreover, the establishment of the index is calculated based on the health of the remaining life of the transformer model.Actual case studies have shown that evidence reasoning and confidence factor α1 and transformer residual life calculation model based on the health of the index are feasible and effective. Through the evaluation of the results, two recommendations have been obtained:fuzzy comprehensive evaluation method in practical applications, evaluation of the number shall not be excessive, it should present the simple and precise form; fuzzy operator shall be depended on its outcome and requests; the practical application of the method of evidence reasoning shall be determined by the confidence factor of the evidence conflicts degrees. When the evidence conflict is large, it’s better to select the calculation method of the confidence factor α1, or other methods suitable for solving large conflict. On the contrary, confidence factor calculation α2, or other suitable lower degree have been utilized in other conflicts. Finally, quantitative assessment of the results were analyzed, the remaining transformer life calculation model based on the health level index of the confirmatory have also been analysed and vertifyed.