NUMERICAL AND LABORATORY SIMULATION OF TRANSFORMER SATURATION DEPENDING ON THE INITIAL PHASE OF THE CURRENT

Abstract

In case of short circuits in electric power systems, emergency modes are possible, accompanied by saturation of transformers. With them, significant distortion of current signals occurs in the secondary winding of the transformer with the appearance of an aperiodic component and harmonics, the level of which is comparable to the signal at the main industrial frequency. The requirements for relay protection and automation devices imply the need to determine the time from the onset of the transient process to the onset of distortion of the current signal in the secondary winding. The purpose of the study is to analyze the saturation of the transformer depending on the initial phase of the transition process. Materials and methods. The PSCAD platform was used to model the power system section. The model makes it possible to qualitatively describe the saturation of a step-down transformer in the event of a short circuit on the low side, taking into account hysteresis phenomena in the magnetic system. Experimental verification was carried out in laboratory conditions using a measuring (intermediate) current transformer. Results. It is shown that, depending on the phase of the current at the moment of the beginning of the transient process, the pattern of saturation and, accordingly, the distortion of the current changes significantly. The distortion of the time waveform of the current signal in the secondary winding of the transformer can begin both after fractions of the period of the power frequency signal, and after several periods. Conclusions. The assessment of transformer saturation modes should be carried out taking into account the fact that the initial conditions for transient processes during short circuits are random. In the analysis of such processes, it is necessary to take into account the phase shift between current and voltage.