Research On Monitoring Method Of GIS Basin-type Insulator Bolt Condition Based On Ultrasonic

This subject is one of the important sub-projects of the State Grid Shanxi Electric Power Company’s scientific and technological research project "Research and Application of Key Technologies for GIS basin-type insulator Stress Detection Based on Ultrasonic".This topic is proposed for the problems of uneven stress distribution and even gas leakage in the basin-type insulator caused by the loosening of the GIS basin-type insulator bolts.With the rapid development of my country’s high-voltage power grid,GIS means gas-insulated metal-enclosed switchgear has been widely used in various substations with its excellent performance.In GIS equipment,basin-type insulator play the role of mechanical support,air chamber isolation and insulation,and is an important part of GIS equipment.Basin-type insulator is mainly fixed by flange bolts,but loose bolts can cause problems such as uneven force of basin-type insulator and even gas leakage,which seriously affect the reliability and safety of GIS operation.In view of the above problems,this article takes252 k V single-phase air-isolated GIS basin-type insulator as the research object,and takes the monitoring of the bolt loosening of basin-type insulator as the main research content,The aim is to put forward an effective method for monitoring the bolt condition of basin-type insulator through theoretical analysis,simulation modeling,experimental research and other links,so as to realize the effective monitoring of GIS basin-type insulator bolt loosening.The specific research content is as follows:Using the reflection and transmission characteristics of the ultrasonic wave on the propagation interface,the propagation law of the ultrasonic wave on the interface of different acoustic resistance is studied,it is found that the ultrasonic wave can only be transmitted between the flange of the basin-type insulator and the flange of the air chamber,and cannot be transmitted from the flange to the air.Based on the statistical contact model and the ultrasonic signal energy model,the relationship between the ultrasonic energy and the actual contact area,contact surface stress and response signal is studied.The energy of the ultrasonic signal and the actual contact area between the flanges are approximately linear,and the peak value of the response signal can reflect the energy of the ultrasonic signal.When the load is within a certain range,the actual contact area and the contact stress between the flanges are linear,and the contact stress between the flanges of the basin-type insulator is determined by the bolt torque.Therefore,the ultrasonic response signal energy can reflect the tightness of the bolts.This conclusion lays a theoretical foundation for the research on the bolt loosening of GIS basin-type insulator.The loosening of the basin-type insulator bolts will cause the problem of uneven stress distribution of the basin-type insulator.The dynamic stress/displacement,acoustic/force coupling and other fields of the finite element platform COMSOL can describe and analyze the problem well.Based on the finite element platform COMSOL,a GIS basin-type insulator stress distribution model was constructed,and the internal stress distribution characteristics of the basin-type insulator under different working conditions of bolts and the contact stress law between bolts and flange were studied.The internal stress of the basin-type insulator is mainly concentrated on the larger curved surface and the connecting structure.Therefore,when optimizing the structure of the basin-type insulator,the arc of the basin-type insulator should be made as smooth as possible under the premise of satisfying the manufacturing process.The stress on the bolt is mainly concentrated at the sharp corner of the bolt head.In addition,when the bolt is loosened,the maximum and minimum contact stresses between the bolt and the flange under different torques will decrease,and as the degree of bolt looseness increases,the degree of stress drop also increases.In addition,the loosening of bolts will reduce the maximum contact stress between adjacent bolts and flange.The above conclusions have guiding significance for the connection of equipment and bolts and fasteners in actual engineering.The propagation of ultrasonic waves through two contact surfaces is a highly nonlinear dynamic problem.The finite element platform COMSOL has a powerful nonlinear calculation function,which is suitable for analyzing and verifying the propagation law of ultrasonic waves on basin-type insulator.Using the propagation characteristics of the ultrasonic wave between the flange of the basin-type insulator and the flange of the gas chamber,a model of ultrasonic transmission energy transfer at the interface of the basin-type insulator flange is constructed.The influence of the number and position of the bolts loosening of the basin-type insulator on the ultrasonic transmission signal is studied,and the root mean square deviation of the ultrasonic signal is used to judge the number and position of the bolts loosening of the basin-type insulator.At the same time,experimental verification is carried out.The research results show that the bolt looseness will cause the ultrasonic transmission signal amplitude to decrease.The larger the number of loose bolts,the more obvious the ultrasonic signal amplitude drops.The distance between the loose bolts and the piezoelectric piece at the receiving end is the main influencing factor of the root mean square deviation of the ultrasonic signal,and there is a positive correlation between the two.At the same time,the number of loose bolts also has a significant impact on the root mean square deviation of the ultrasonic signal.When the number of loose bolts increases,the root mean square deviation of the ultrasonic signal will also increase.In order to further characterize the looseness of bolt,the influence of the degree of bolt looseness of basin-type insulator on the ultrasonic transmission signal is studied through experiments,and the ultrasonic signal energy attenuation rate is proposed as another technical indicator of bolt looseness.The research results show that when the amount of bolt looseness is constant,the greater the degree of bolt looseness,the greater the energy attenuation rate of the ultrasonic response signal.At the same time,the distance between the ultrasonic signal excitation source and the ultrasonic receiving sensor is also a factor that affects the energy attenuation rate of the ultrasonic response signal,the ultrasonic receiving sensor closer to the excitation source is more sensitive to the change of the ultrasonic signal energy attenuation rate.Through theoretical analysis,simulation modeling and experimental verification,the monitoring method of GIS basin-type insulator bolt condition is studied,The technical indicators to characterize bolt looseness are proposed,which are the root mean square deviation of the ultrasonic signal and the energy attenuation rate of the ultrasonic signal,they can make judgments on the number of loose bolts,the position of loose bolts and the degree of loose bolts,and realize the monitoring of the loosening state of GIS basin insulator bolts.