Моделювання асиметричних динамічних режимів трифазних трансформаторів

Abstract

The paper analyses the aspects of the need to research the dynamic modes of transformers, which are the most important element of power grids. The types of mathematical models that are used to research the dynamic modes of transformers are considered. Arguments in favour of 3-axial mathematical models are presented, which have wider possibilities for modelling various operating modes. The paper aims to determine a universal variant of a mathematical model suitable for studying asymmetric operating modes of a transformer. The paper proposes a variant of a 3-axial mathematical model based on a generalized electric machine model. A modernized variant of the model was used, which takes into account the power losses in the magnetic core. To be able to model asymmetric modes with its help, a phase-by-phase separation of parameters was performed and the corresponding calculated coefficients were introduced. The equations of currents are presented taking into account the phase-by-phase separation of their parameters. For the proposed model, transients for one symmetric (switching on the transformer at full load) and two asymmetric (switching on when a short circuit in one phase and switching on when phase failure) modes were calculated. As sources of asymmetry, the accidents in the secondary circuit of the transformer were considered. Modelling was performed on alternating current. The analysis of the obtained curves showed that the proposed model and methods of its application make it possible to adequately model a wide spectrum of dynamic modes of a transformer without the need to use the decomposition of asymmetric systems of quantities into a set of symmetric components, which essentially simplifies the modelling process. The analysis of asymmetric modes showed that they are characterized by an asymmetry of the transformer currents in amplitude and angle, and in the case of a phase failure, a significant difference in the pattern of currents in the primary and secondary windings is observed.