Analysis Of Voltage Distribution Characteristics Of Transformer Windings Under Lightning Intruding Surge Wave In 220kV Substation

As the hub of power system,the substation plays an important role in transforming voltage,collecting and distributing electric energy.Once the transformers which don’t have self-recovery ability of insulation are damaged by lightning,it will cause power failure of the power grid,and then bring a significant impact on production and life.Operation experience shows that most of lightning accidents in substations are caused by lightning striking electric transmission lines.The intruding surge wave cased by lighting transmission lines is the main factor damaging of substation equipment,it has great engineering signality to ensure the operation safety of transformers by analysing overvoltage characteristics of transformers under intruding surge wave.In this paper,the lightning surge overvoltage and its influence on the voltage distribution in the transformer windings in a 220 k V substation in Tianjin were calculated based on the Electro-magnetic Transient Program(EMTP/ATP).And the characteristics of voltage distribution in transformer windings were analyzed under the special working condition of winding deformation,which provided a theoretical reference for the lightning protection of transformer.The main work of this paper is as follows:1.A simulation model of lightning surge overvoltage in the 220 k V substation was constructed by EMTP,in which the effects of corona loss and transient grounding resistance on overvoltage calculation were considered respectively by establishing the corresponding circuit model.Furthermore,the lighting surge overvoltage of equipment was calculated,and the effects of corona loss,tower grounding resistance,tower grounding resistivity and incoming cable length on intrusion wave overvoltage were analyzed.The results showed that the waveform of the overvoltage was attenuated and distorted by the corona loss.The change of tower steady-state grounding resistance had little effect on the amplitudes of overvoltage.The overvoltage at the end of the cable was higher than that at the front,the amplitudes of overvoltage at both ends of the cable were reduced by the increase of the cable length.The simulation results were closer to the actual working conditions considering the effects of corona loss and transient grounding resistance.2.The equivalent parameters of the transformer were calculated based on the internal structure of power transformer and the calculation method of equivalent parameters.Meanwhile,the trapezoidal equivalent circuit of multi-winding transformer considering high and medium voltage windings was built.The influence of axial deformation and radial deformation on the maximum voltage distribution of the winding were simulated respectively,and the influence of the degree and position of winding deformation on the maximum voltage distribution was analyzed based on the wave process of transformer windings under the impact of lightning surge overvoltage and the forms and characteristics of winding deformation.The results showed that it had more influence on the maximum voltage distribution in windings with increasing the deformation degree.The maximum voltage of the deformed side of high voltage winding was increased(decreased)by axial(radial)deformation.In addition,the maximum voltage distribution in the medium voltage winding was almost not affected by the axial(radial)deformation in the high voltage winding.In the case of radial deformation in the medium voltage winding,the maximum overvoltage at the deformation position of medium voltage winding and the opposite position of high voltage winding were either reduced.And it had no obvious effect on the maximum voltage distribution in the high or medium voltage winding by the axial deformation in the medium voltage winding.