engleski

Research of insulation design criteria – application of different methods

To design reliable and optimized transformer insulation it is necessary to establish a system of appropriate design criteria where each criterion is related to relevant part of transformer geometry. Physical process of breakdown in liquid dielectrics, including mineral oil, is complex and still under research. In the absence of uniform and widely accepted breakdown theory for oil-immersed transformers design criteria are derived experimentally by testing models that simulate certain part of transformer insulation. In the paper, the process of research of an insulation design criterion is described for specific problem – combined stress at lightning impulse test for HV windings. The goal of combined stress testing was to check the influence of radial stress on permissible axial stress of transformer coil insulation at lightning impulse test. Several well-known criteria have been applied and some results are presented in paper. None of applied methods (criteria) has made satisfactory agreement with tested physical models. It means that the results of application were not in accordance with logical expectations. Therefore, additional analyses had to be made. Due to geometry complexity, it is decided to search design criterion using genetic algorithm. This method is generally powerful tool for solving multi-parametric problems which are very often difficult to solve using classical approach. Use of known criteria means use of certain functions. New approach with genetic algorithm assumes mathematical model in general form where model parameters are varied to satisfy certain condition. New procedure is described more in details. Use of genetic algorithm resulted in useful insights and possibly promising results.

oil-immersed power transformer ; winding insulation ; model ; insulation design criterion ; lightning impulse ; genetic algorithm

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