Evaluation of Autotransformer Residual Magnetization Impact on the Conditions of Resonant Over Voltages Development
Keywords:
autoparametric resonance, SF₆ circuit breaker, resonant overvoltages, residual magnetization, switching instant, controlled switching deviceAbstract
The article describes the use of a controlled switching device for switching on a single-phase autotransformer 750/330/15.75 kV, with a capacity of 417 MVA in the main electrical network of Ukraine. The basis of the study was the development of a detailed model of electromagnetic transients of the autotransformer. The transformer model contains an accurate reproduction of hysteresis and residual magnetization, which was confirmed using real oscillograms and manufacturer's data. The article considers the use of a controlled switching device for switching on an autotransformer with a capacity of 333 MVA, with a voltage of 750/330/15.75 kV in main electrical networks. A methodology for assessing the degree of risk of resonant overvoltages, taking into account the phase angle of switching on and the depth of saturation of the magnetic core, has been developed. The paper presents a comprehensive study of the influence of residual magnetization and the switch-on angle on the amplitude and dynamics of the aperiodic component of the magnetic flux during switching of high and extra-high voltage transformers and autotransformers. The dependence of the aperiodic component on the instantaneous value of the sinusoidal component and the residual flux was analytically obtained, which allowed establishing the condition for complete compensation of the aperiodic component. Based on numerical experiments, it is shown that the correct choice of the switch-on angle is able to almost completely eliminate the aperiodic component, while uncontrolled switching generates magnetizing current and overvoltage spikes, the amplitude of which can be 200...250 times greater compared to controlled modes. The modeling confirmed the universal exponential nature of the damping for all switch-on angles and revealed the dominant influence of the initial amplitude. The results demonstrate the critical importance of residual flux estimation and phase-by-phase synchronization of the switching moment for minimizing overloads, reducing the probability of resonance processes, and increasing the reliability of the main electrical networks. The obtained dependencies and the proposed algorithm for determining the optimal switching angle form a theoretical and practical basis for the implementation of controlled switching devices (CSDs) in high and extra-high voltage networks, ensuring improved electromagnetic compatibility and extending the equipment life.
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