Research On Residual Magnetism Of Power Transformer Core

The power transformer is one of the most important equipment in the power system.As the main ‘killer’ of power system safety,magnetizing inrush current often occurs in the operation of power system.As a kind of electrical equipment made of high magnetic permeability using ferromagnetic materials,the hysteresis characteristics of ferromagnetic materials will inevitably affect.The electromagnetic performance and operational stability of the transformer,the most important of which is the effect of residual magnetism on the excitation current of the transformer.In most cases,the initial magnetization curve is adopted in the electromagnetic analysis of transformers,which is fast in calculation speed and can guarantee certain accuracy,but cannot reflect the hysteresis characteristics of ferromagnetic materials.The influence of hysteresis loop must be considered when studying the remanence of transformer core.Based on the magnetic properties of ferromagnetic materials,the reason of the residual magnetism in ferromagnetic materials is analyzed based on the magnetic domain theory.Taking the single-phase transformer as the research object,the variation law of the internal magnetic flux of the core under the condition of residual magnetism and no residual magnetism during the no-load closing of the transformer is analyzed.The main flux and excitation of the transformer core are realized by using the simulation software of Magnet.Simulation analysis of the relationship between current changes.The Jiles–Atherton hysteresis model for simulating the hysteresis characteristics of ferromagnetic materials is deduced and modified.The hysteresis loop is calculated by the modified JA hysteresis model by discrete integral method.The core loss separation theory is applied to base on the law of conservation of energy,the dynamic JA hysteresis model is derived.The difference between static JA hysteresis model and dynamic JA hysteresis model is compared,and their hysteresis loop comparison graphs are obtained.The accuracy of the JA model parameters plays an important role in the application of JA theory.The particle swarm optimization algorithm is used to identify the parameters of the JA hysteresis model,and the influence of each parameter on the magnetization curve is analyzed.Based on the JA theoretical model,the mathematical model of the single-phase transformer is established.The JA theory is applied to the transformer model by using the real-time magnetic permeability of the core and the magnetic permeability of the transformer mathematical model.The simulation circuit is built on Matlab/Simulink platform.The influence of JA model parameter variation on excitation current waveform and the relationship between excitation current and residual magnetization are simulated and analyzed.