Analysis Of Power Transformer Inrush Current Influencing Factors

Power transformer is an essential electrical equipment in the power system, which has complexes operating conditions. When the transformer is switched on or the transformer terminal voltage is restored immediately after removal of the external fault. The residual flux may cause the transformer core deeply saturation, and leading to a very large transient excitation current, which is inrush current. The inrush current which may cause the harmonic pollution, the ferromagnetic resonance, and the grid voltage sag, in addition to the cause of transformer differential protection mis-operation, also may cause harm to the power system. However, the research of the inrush current under various influence factors has practical significance to improve the performance of the transformer, and improve the quality of the power system.Firstly, to the discussion of the influence factors of inrush current, the expression of power transformer inrush current is deduced theoretically. Through MATLAB, the simulation model of single-phase or three-phase transformer under no-load switching condition has been built respectively. The simulation results of the characteristics of inrush current waveform have been analyzed and the influence factors of inrush current in the same case of other conditions have been analyzed either.Furthermore, by studying the J-A hysteresis model loop, iteration method was proposed for solving five parameters, and uses the hysteresis loop alternate the magnetization curve of transformer core permeability. The hysteresis loop under different residual flux was got through the simulation circuit built by SIMULINK on the basis of J-A model of differential equations. The advantage of alternative magnetization curve hysteresis loop can more accurately get the relationship between the transformer primary side voltage and the exciting current.Based on the improved J-A hysteresis model, the mathematical model of the single-phase and the three-phase transformer were established. The research of the waveforms of the inrush current has been considered by the established simulation model. Under different influencing factors of the single-phase and three-phase transformer to get the exciting current waveforms respectively. Through comparing, discussions of the influence of the inrush current under different factors, that verified the correctness of the theoretical derivation and analysis.