Research On Ultrasonic Testing Method For Interface Defect And Thermal Stress Of GIS Basin Insulator

Gas insulated metal enclosed switchgear(GIS)has the advantages of high reliability,small influence by external environment factors,convenient maintenance,compact structure,short installation period,flexible configuration and strong scalability,and is especially suitable for substations,underground substations in crowded areas in big cities and steep mountainous areas.Basin insulator is the key part of GIS,and the interface between the center conductor and epoxy insulation of basin insulator is the most complex part of the basin insulator.The stress concentration phenomenon is obvious,especially the thermal stress during operation,which is easy to cause mechanical damage of the basin insulator,leading to interface defects and insulation failure,threatening the safe and reliable operation of GIS equipment.Therefore,it is of great significance to study effective methods of detecting interface defects and thermal stress of basin insulator,to explore the distribution characteristics of thermal stress of basin insulator,to understand the mechanism of thermal stress concentration evolving into interface defect,which is of great significance to evaluate the stress state of basin insulator,prevent interface defects,avoid the occurrence of isolated faults and ensure the safe and stable operation of GIS equipment.Firstly,the ultrasonic detection principle of the interface defects and thermal stress of the basin insulator is introduced,and the corresponding ultrasonic testing system is established.Through theoretical analysis of various testing methods,the ultrasonic detection method suitable for the interface defects and thermal stress of the basin insulator is determined;the ultrasonic propagation model of interface defects is established based on the geometry structure of the basin insulator,and the calculation formula of the defect depth and detection range is obtained;the relationship between stress and strain and acoustic time is deduced by fixed sound history;finally,the relationship between stress and strain and sound time is established The ultrasonic testing system,which is used to evaluate the sensitivity of the ultrasonic testing system,is introduced.Secondly,the ultrasonic testing of the interface defects of the basin insulator is carried out.The interface defects of 126 k V Three-Phase common box insulator are detected by the method of double probe ultrasonic longitudinal wave reflection and ultrasonic phase controlled flexible coupling.The interface defects of the basin insulator are detected by the double probe ultrasonic longitudinal wave reflection method.A small diameter low frequency ultrasonic straight probe is developed for interface defect detection.The interface defects are determined according to the received reflection wave;then the interface defects of the basin insulator are detected by the ultrasonic phase control flexible coupling method.The method combines the water bag as wedge and ultrasonic phase control array probe to solve the boundary In the face defect detection,the coupling between the probe and the basin insulator is difficult.Ultrasonic wave is incident to the basin insulator through the water bag,and the interface defect is determined according to the received reflection wave.Based on the above two detection methods,the interface ultrasonic propagation model is established,the corresponding ultrasonic detection system for interface defects is built,the amplitude is selected as the characterization parameter of the defect,the size and position of the interface defects are detected.The results of the ultrasonic longitudinal wave reflection method and ultrasonic phase control array method are analyzed,which provides an effective method for the detection of the interface defects of the basin insulator.Finally,the distribution of thermal stress and strain of the basin insulator is studied.The thermal stress and strain of the normal interior and radial subsurface of the epoxy insulation material of 252 k V single-phase basin insulator are detected by ultrasonic longitudinal wave reflection method and critical refraction longitudinal wave method respectively.Firstly,the normal internal thermal stress of the basin insulator perpendicular to the epoxy insulation is detected by the single probe longitudinal wave reflection method.The upper and lower surfaces of the detection area are parallel,and the thickness is 19 Then,the critical refraction longitudinal wave method is used to detect the thermal stress on the radial subsurface of the basin insulator,and the variable angle longitudinal wave probe with appropriate frequency is selected to fix the sound path,and the sound time(ultrasonic propagation time)is taken as the measurement object.Based on the above two thermal stress detection methods,a thermal stress ultrasonic detection system is built.The temperature load is applied to the central conductor to simulate the temperature field of basin insulator under actual working conditions.The acoustic time is used as the characterization parameter of thermal stress,and the acoustic time at different positions of basin insulator is measured.According to the relationship between acoustic time and stress,the distribution law of thermal stress of basin insulator is analyzed,the foundation of the stress state assessment of the insulator is established.