Analysis And Treatment Of Typical Defects In Oil-paper Insulation Bushing Of Transformer

The high voltage power transformer bushing is the basic connection between the outer conductor and the inner conductor,and is an important part of the power transformer.It has the function of introducing or drawing high voltage and large current from the metal case.The bushing is the weak link of the transformer.The failure process of the bushing is not easy to identify.A failure may cause a minor failure of the bushing or the entire transformer.Data analysis shows that more than 30% of main transformer failures are caused by bushing failures.The study found that the most critical part of the insulation of oil-paper insulated bushings is the internal capacitor core,so the capacitor core is an important component for monitoring the status of the bushing.This paper takes the oil-paper insulated bushing of transformer as the main research object,and studies its typical defects and faults through four aspects of theory,simulation,optimization and experiment,focusing on the analysis of the deterioration process of bushing damp defects.First,theoretical analysis.Statistical analysis of the typical defect types,manifestations,fault locations and other related data of transformer oil-paper insulating bushings,and the main defect types are obtained.Moisture is one of the typical defects of oil-paper insulated bushings.It is of great significance to study the electrical characteristics of bushings when they are damp.By analyzing the deterioration mechanism of the damp defect of the bushing,the influence of damp on the electrical performance and operating life of the oil-paper insulated bushing is further analyzed.Second,simulation.A simulation model for the insulation structure and damp defects of transformer 500 k V and 72.5k V oil-paper insulation bushings is established.The internal electric field under three conditions of good drying,uniform damp and non-uniform damp is simulated and studied,and the position of the maximum electric field intensity and the degree of degradation under the corresponding conditions are obtained.Analyze the influence of uniform and non-uniform damp on the dielectric loss value,FDS curve and internal electric field distribution of oil-paper insulating bushings.The study found that the dielectric loss value of 0.001 Hz in the FDS low frequency band is more obvious,which is of positive significance for on-site detection.In actual operation and maintenance,the dielectric loss value measurement of this frequency band should be added to detect the damp condition of the casing as soon as possible.Third,algorithm optimization.By using the Nelder-Mead method and the coordinate search method to optimize the sleeve capacitor core,the results show that changing the length and thickness of the capacitor core can reduce the maximum electric field intensity,thereby reducing the possibility of partial discharge,and effectively avoiding corona discharge or The breakdown phenomenon occurs.And through training the BP neural network,the corresponding model is obtained,and on this basis,the genetic algorithm is used for optimization,and the optimized capacitance core length and thickness variable values are obtained,so that the maximum electric field intensity of the capacitor core is optimized solution.The optimized parameters are substituted into the COMSOL software for calculation,and the numerical error obtained is within the allowable range,which proves the effectiveness of the optimization model.Fourth,test verification.Through the establishment of a test platform,the evolution process of key characteristic values such as dielectric loss value and capacitance under the rated voltage and working conditions of the damp defect model of the transformer oil-paper insulated bushing,as well as the change law of the frequency domain dielectric spectrum,are studied.At the same time,a step-up test was carried out,and the voltage value that caused a serious dielectric loss value to exceed the standard was obtained.According to the test results,the effective feature quantities that can objectively reflect the deterioration process of the transformer oil-paper insulating bushing are extracted,and the corresponding judgment basis is provided for on-site operation and maintenance.