Analysis Of The DC Bias Characteristics Of Power Transformers Caused By Rail Transit And Research On The Suppression Measures

Urban rail transit is a relatively convenient way to travel today,and subway not only can alleviate traffic congestion but also has the strong support of the government because of its"convenient and green" travel characteristics,and has become the best solution to alleviate traffic congestion.In recent years,government departments across the country have issued policies to increase investment in subway construction and its operation and management.As the planning and construction of the subway is in full swing,some problems caused by the subway also follow.Because the subway power supply system uses DC power supply,the stray current during subway operation will invade the transformer through the neutral point of the transformer,causing a series of electromagnetic effects of the transformer,such as local overheating and noise of the main transformer,which will threaten the safe operation of the power grid in severe cases.In order to eliminate the influence of DC bias,it is necessary to analyze the vibration and noise characteristics of the transformer when DC bias occurs,so as to find the best suppression measures and control the vibration noise from the source.The paper uses COMSOL Multiphysics software,and takes 220 kV transformer in a substation in Changsha area as the research object,and its model is SF9-180000/220.In this paper,the actual transformer model is replaced by an equivalent circuit and a magnetic circuit model to build a 220kV transformer simulation model.Simulation and analysis of the vibration and noise of the transformer under DC bias,involving the coupling of the four physical fields of magnetic field,circuit,structural force field and sound field,and calculation of the magnetic flux density and deformation under normal DC bias current and under the influence of DC bias current,Noise and other distribution rules,Fourier transform the noise signal to obtain the frequency domain distribution map of transformer noise.Finally,an experiment was conducted to analyze the measured data to analyze the vibration and noise characteristics of the transformer during DC bias,and the effectiveness of the simulation model was verified.The thesis further discusses the DC bias magnetic suppression measures,and selects a capacitor DC blocking device from the engineering practice to analyze its suppression effect and its impact on the normal operation of the power system.The simulation results show that the intrusion of DC into the transformer will cause the magnetic flux density on the iron core to change,and the positive and negative cycles are no longer symmetrical,and the magnetic flux density on the iron core will increase with the increase of the DC amount.Phenomenon;the displacement law of the iron core due to magnetostriction is consistent with the change law of magnetic flux density.The displacement increases in the positive half cycle and decreases in the negative half cycle;and as the amount of DC bias increases,the magnetostriction increases.In turn,the vibration of the iron core is increased and the noise of the transformer is increased;the noise of the iron core in the same transformer is greater than the noise of the winding;the experimental data is roughly consistent with the simulation results,and the validity of the model is verified.The capacitor DC blocking device can effectively suppress DC bias and have little effect on the power system,and can be widely used in engineering examples.