Research On The Models Of Reliability Evaluation And Fault Diagnosis Of Oil-immersed Power Transformers

Oil-immersed power transformer, as an important constituent part of electric system, is a hub for electric energy transmission and transformation, and its steady running relates to electric system’s safety, reliability and economical efficiency. Therefore, accurately evaluating its running reliability, timely diagnosing its internal fault type and mastering fault development trend hold great significance for electric system. Oil-immersed power transformer is a complex aggregation of several sub-systems, and each sub-system has a different contribution degree to transformer’s reliability. Winding oil-paper insulation system is the core and also the most weak part of transformer; once it failed, the transformer may be caused to stop running; and if treatment is not conducted timely, transformer’s service life may be caused to terminate. Thus, accurately evaluating its running reliability and rapidly identifying potential faults have been always the research focus. As limited by transformer’s structure, oil-paper insulation system is placed inside the transformer; unless the windlass cover is disassembled for overhaul, it is difficult to directly evaluate the oil-paper system; so only indirect method- evaluation by modeling- can be adopted according to information about status of transformer showed during running.Regarding transformer reliability evaluation, in this paper, taking the winding oil-paper insulation system as the foothold for evaluation, a differentiated reliability evaluation model is established in combination with running state information quantity of the object itself to be evaluated. This model is of a framework of basic aging model + grey modification model, of which the basic model, selecting hot-spot temperature(HST) as the starting point for modeling, establishes a model for evaluating the reliability of oil-paper insulation system at normal aging conditions in combination with Weibull distribution(Weibull) and Arrhenius reaction law. The dynamic modification model takes equivalent hot-spot temperature as the modification core, integrates and processes power transformer’s state information adopting grey theory, quantifies the effect of overhaul on transformer’s reliability based on age reduction theory, and fully considers the individual difference during reliability evaluation. The framework of basic model + dynamic modification model ensures that reliability model can well trace transformer’s actual health status, so as to improve evaluation accuracy.In regard of transformer fault diagnosis, DGA sample data is taken as the basic data for reliability evaluation and fault diagnosis in this paper. Focusing on the disadvantages of incomplete code coverage and low diagnosis accuracy of three-ratio method and improved three-ratio method, a fault diagnosis model based on colonial competitive algorithm optimization related vector machine is proposed in this paper, and in term of other diagnosis methods, the objective of improving fault diagnosis accuracy is attained.