| The construction of energy internet is leaded by China through extra-high voltage(EHV)and ultra-high voltage(UHV)power grid,as the most used type of insulator for EHV and UHV transmission lines,composite insulators have exceeded 10 million by 2021.After several generations of innovations in production technology,composite insulators have greatly reduced the probability of ordinary mechanical fractures and brittle fractures.However,in recent years,decay-like breakage accidents of composite insulators occur frequently in the high-humidity areas of China,which seriously threatens the safe operation of power grid.The decay-like composite insulators are often accompanied by abnormal heating during operation,and the phenomenon of heat generation is especially obvious in a high humidity.Infrared imaging technology is an effective means to diagnose the decay-like composite insulators.But due to the lack of understanding of the decay-like deterioration mechanism of composite insulators under the combined action of multiple factors and the temperature rise characteristics under different environmental conditions,there is still a high false detection rate in the diagnosis of decay-like composite insulators.Therefore,it is of great significance to carry out research on the decay-like deterioration mechanism and temperature rise characteristics of composite insulators in high humidity environment to ensure the safe operation of the power grid.Related researches are carried out on the mechanism of decay-like deterioration of composite insulators,the simulation test method of decay,the abnormal heating mechanism and temperature rise characteristics of decay-like composite insulators,and the infrared diagnosis method in this paper.The main research work is as follows:(1)According to the operation,environment and mechanical load characteristics of the compact line V-string decay-like composite insulators,the numerical simulation method was used to analyze the action mechanism of the deterioration of the composite insulator rod material(glass fiber reinforced plastic)by external moisture in high humidity and the damage evolution process of materials under alternating buckling loads from a meso-scale.The results showed that under the action of high humidity and alternating load,the outer side of the buckling arc on the surface of the rod will appear fatigue damage developed from the outside to the inside,and micro-defects will be generated at the matrix and interface,causing partial discharge that degraded the epoxy resin matrix.The surface discharge on the rod and the internal electrical tree leaded to the local carbonization of the rod.External moisture,partial discharge and alternating load were the three main factors affecting the decay of composite insulators.During the decay-like process of composite insulators,the three had their own action mechanisms and promote each other.(2)A multi-factor composite insulator decay-like test platform based on wet,electric,and alternating load was built,the composite insulator decay-like simulation test method was proposed,and the relevant test parameters were determined.The decay-like degradation mechanism of composite insulator rods under the interaction of wet,electric and alternating loads was revealed.During the deterioration process,the rod experienced successively the process of surface damage,increased damage,fatigue brittleness,local erosion,decay-like deterioration.The epoxy resin matrix experienced the stages of swelling,interfacial delamination,cracking and damage,acid corrosion dissolution,melting and pyrolysis,etc under the combined action of high humidity,partial discharge and alternating load.Some glass fibers surface were corroded and there were electro-erosion holes of different sizes and typical fatigue fracture cross-section characteristics.The equivalence of simulated decay-like composite insulators and real decay-like composite insulators was verified with the help of appearance and morphology analysis,scanning electron microscope,fourier transform infrared spectrometer and thermogravimetric analysis.(3)A four-electrode system test was used to measure the surface current,volume current and interfacial current of typical short samples of the decay-like composite insulator.By building an equivalent circuit model of a full-scale decay-like composite insulator and typical short samples,the contribution rate of the leakage conduction loss and polarization loss of the decay-like composite insulator to the temperature rise in high and low humidity was analyzed,revealing that the temperature rise of the decay-like composite insulator was mainly caused by the polarization loss of the decay-like part in high and low humidity,and the external moisture mainly affected the temperature rise of the composite insulator by affecting the polarization loss.It is clarified that the dielectric loss factor,saturated moisture absorption rate and saturated moisture absorption dielectric loss of the decay-like part of the rod in the high humidity were the main physical quantities that affected the temperature rise of the decay-like composite insulator.Further according to the periodic change law of temperature rise characteristics,moisture absorption characteristics and dielectric loss characteristics in the process of decay-like deterioration of composite insulator,the decay degree of composite insulators was divided into four grades of light,medium,heavy and extremely heavy,then the temperature rise ranges corresponding to different decay-like degrees were obtained in high and low humidity.The temperature rise characteristics of 500kV abnormal heating composite insulators under different decay-like degrees were studied through experiments and the correctness of the division of the corresponding temperature rise ranges under different decay-like degrees was verified.(4)A super-resolution reconstruction method of composite insulator infrared images based on super-resolution generative adversarial network was proposed,which improved the clarity of images and unified the resolution of images.Through statistical analysis,the temperature rise gradient characteristic coefficient based on the temperature rise gradient curve of the composite insulator axis was proposed as a new characteristic quantity,and then a multi-feature infrared diagnosis method for decay-like composite insulators based on the temperature rise degree,temperature rise area characteristics and temperature rise gradient characteristic coefficient in high humidity was proposed.Through the degree of temperature rise,heavy and extremely heavy decay-like composite insulators with a temperature rise greater than 10K can be initially diagnosed,and through the temperature rise area characteristics,light or medium decay-like composite insulators with a temperature rise within 10K but with more than one temperature rise area or a temperature rise area extending from the high-voltage end fitting to the back of the five sheds can be diagnosed,and through the characteristic coefficient of temperature rise gradient,light or medium decay-like composite insulators with the temperature rise between 2K and 10K and the temperature rise area only located between the second and fifth sheds of the high voltage end but temperature rise gradient characteristic coefficient less than 0.5 can be diagnosed.The research conclusions provided new ideas for improving the screening accuracy of decay-like composite insulators. |
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