Harmonic Characteristic Analysis Of Inrush Currentin Transformer No-load Closing

With the rapid development of China's economy,the supply of electric energy has gradually become the energy burden for China's social and economic development,and electric energy is also related to the national energy security and the lifeline of the national economy.In recent years,with the improvement of transformer materials and the gradual increase of rated operating point,the recognition ability of traditional second harmonic braking principle has decreased.Therefore,it is of practical significance to study the generation mechanism of inrush current,influencing factors and harmonic characteristics analysis of waveform to improve the ability of second harmonic braking device to avoid inrush current and to improve the safe and stable operation ability of power system.Starting from the generation mechanism of transformer inrush current,this paper theoretically studies the influencing factors of inrush current with a simplified transformer model.The harmonic content of inrush current is calculated by fitting BH curves with two and three polylines respectively.The variation characteristics of harmonic content of unidirectional inrush current and symmetric inrush current with various influencing factors are calculated,and the reason why the second harmonic content of inrush current is lower than the set value is analyzed.Through the design drawings of single-phase transformer and three-phase transformer,a magnetic circuit coupling model is built on Flux platform to verify the accuracy of the model,and then the tests of transformer no-load switching inrush current under different influencing factors are simulated,and the simulation results are studied.According to the simulation results,the characteristics of the inrush current are analyzed to verify the accuracy of theoretical calculation and analysis.In addition,a circuit model with only circuit connection is established in MATLAB through the basic electromagnetic formula,and the advantages and disadvantages of the circuit model and the magnetic circuit coupling model are compared,and the setting value of the second harmonic braking device is discussed in combination with the field test data of the nuclear power plant.