Study On Partial Discharge Characteristics And Suppression Of Main Insulation Of Transformer Oip Capacitive Bushing

OIP（Oil Immersed Paper）capacitive bushing is an essential outlet device of transformer.However,with the gradual increasing of voltage level,bushing failures frequently happen.Partial discharge is the main cause of bushing insulation failure.Therefore,it is of great significance to effectively reduce the partial discharge of bushing for safe and stable operation of power grid.In this paper,the main insulation of BRY（l）-126/1200 OIP capacitive bushing was taken as the research object.By means of simulation analysis and experimental research,the research on partial discharge of OIP and OIP bushing under working conditions,optimization of main insulation structure and modification of main insulation materials based on partial discharge suppression were carried out.The main contents of this paper are as follows:（1）Nano-Ti O₂ was used to modify insulating oil paper in laboratory.Laboratory samples of unmodified insulating paper and modified insulating paper with mass fraction of 1%,3%,5%and7%were prepared.A measuring platform for dielectric and partial discharge characteristics of OIP was set up to explore the influence of temperature on dielectric properties and PDIV（Partial Discharge Inception Voltage）of OIP.The experimental results showed that,with the increasing of temperature,the dielectric constant of insulating oil paper increases because of the improvement of cellulose molecular polarization ability.The increasing of dielectric constant leads to the partial higher voltage and the value of PDIV in OIP.（2）The model of OIP capacitive bushing was established,and the electro-thermal coupling simulation of 126 k V bushing was carried out by using finite element analysis software,and the influence of working conditions on partial discharge of main insulation for the bushing was analyzed.The simulation results showed that the high temperature region was concentrated in the middle and lower parts of the current-carrying conductor and capacitor core and distributed in trapezoidal shape.The temperature of the capacitor core first increased and then decreased along the axial direction,and continued to decrease along the radial direction.The highest temperature appeared at the zero screen,and its partial discharge margin decreased by 14.3%.Considering the influence of temperature gradient on casing under operating conditions,a set of calculation scheme of casing equal margin under operating conditions was designed to improve the local discharge starting voltage of casing main insulation.The results showed that the design scheme could increase the PDIV of BRY（l）-126/1200 OIP capacitive bushing by 17.1%.（3）The insulating paper was modified by Nano-Ti O₂ particles to increase the PDIV of OIP.The research showed that with the addition of Nano-Ti O₂ particles,the PDIV value of OIP increased,and the PDIV value is the highest when the mass fraction is 5%,and the modification effect has a certain temperature stability.