Analysis of the processes in power and measurement transformers and correction of their description for various applications
Transformers are widely used both for power conversion and for measurements in various practical applications. In this case, it becomes necessary to take into account the nonlinearity of their transfer characteristics. For example, in the calculation of transient processes for the development and design of modern relay protection, recording of abnormal occurrences in power systems, the regulation of various modes and other purposes. Many problems can be solved by using excitation current filters and reproducing of primary and secondary currents of the transformers. In this connection, the article deals with the solution of the problems of filtering the excitation current and reproducing of secondary currents for step-up and step-down transformers in terms of a single-phase, three-winding transformer, which is a prototype for other types of transformers. In the opinion of the authors of the article, in this case it is necessary first of all to ensure the stability of the computational process of the filter and to reduce its method error due to the neglect of the hysteresis of the excitation characteristics. For what the article proposes a refined mathematical model of the electromagnetic system of the transformer. Next, the physical implementation of the model is proposed. The successful results of the computational experiment based on it, which are displayed on the presented oscillograms of individual values, excitation characteristics, phase portraits on the phase plane are described in detail. Besides, the results of analysis of the short circuit on the outgoing line of the transformer are given. The results of the analysis indicate the significant influence of the transfer characteristic nonlinearity of the transformer on the values recorded from its primary and secondary sides. This can be taken into account when developing new relay protection devices for other emergency control systems, and recording devices of abnormal occurrences.