Abstract
The paper analyses the aspects of modelling the operation of a three-phase core-type transformer. The features of the magnetic system construction of the transformer, which generate asymmetry, are disclosed. The fundamentals and methods for modelling a transformer in dynamic modes are considered. The main purpose of the paper is to research the influence of taking into account the asymmetry of the transformer magnetic core on its dynamic model. The paper proposes the mathematical model of a three-phase planar core-type transformer, which takes into account the asymmetry of the magnetic core. The mathematical model is based on the model of a generalized electric machine in the ABC axes, which is widely recognized and characterized by a high level of adequacy. A refined model, which takes into account the power losses in the magnetic core, has used. As is well known, such a model is characterized by higher accuracy and adequacy in the calculation of transient processes. For the proposed mathematical model, a comparative analysis of the calculated curves of transient processes for a 63 kVA transformer with a voltage of 6 / 0.4 kV is made. To disclose the effect of taking into account the magnetic core asymmetry of the transformer in the mathematical model, the current differences were calculated in pu for the modes of switching on at full power and three-phase short circuit. These modes are the most common and indicative in the analysis of the operability and stability of transformers. It was found that the most significant difference, which is obtained by taking into account the magnetic system asymmetry of the transformer, is 5…6% when it is switched on at full load. Thus, the relatively simple transformations and updating of the mathematical model of the transformer allow significantly increase its adequacy. The proposed mathematical model can be more effectively used when the non-typical design of three-phase transformers or reactors with significant asymmetry of the magnetic core is considered.
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