Due to long-term exposure to high electrical field strength, heavy loads, and the complex climatic conditions in tropical coastal areas of China, widespread abnormal heating phenomena often occur in the operation of composite insulators in power transmission lines, posing a threat to the safe and stable operation of the power system. To study the ageing process of the silicone rubber sheath of composite insulators in the high-field, high-humidity, high-temperature, and high-salt-density environments along the coastal regions, this paper establishes a humidity–heat–electricity–salt spray accelerated ageing test platform and conducts ageing tests on silicone rubber materials for composite insulators under the coupled effect of multiple factors. The ageing characteristics of silicone rubber materials are analyzed using scanning electron microscopy, Fourier infrared spectroscopy, thermogravimetric analysis, and other methods. The results show that the coupled ageing factors have an impact on the surface morphology of silicone rubber. The continuous depolymerization of PDMS molecular chains leads to a decrease in the content of groups related to the hydrophobicity of the material, resulting in a deterioration of its hydrophobicity. Moreover, the degradation of silicone rubber materials and the enhanced moisture absorption capacity lead to an increase in the dielectric loss tangent of the saturated moisture-absorbing medium, thereby causing abnormal heating of the sheath at the end of the composite insulator. The research findings of this study are of significant reference value for revealing the degradation mechanism of composite insulator silicone rubber sheaths in tropical island environments and improving the service life of composite insulators.

Insulators are the basis of the stable operation of transmission lines, and it is particularly important to regularly detect the insulation performance of insulators. After several years of research, contactless space electric field detection technology for degraded insulators, based on an unmanned aerial vehicles (UAV) platform, has developed rapidly. However, the existing technology is only limited to the typical vertical/horizontal state research category and cannot apply to complex operating conditions such as attitude disturbance and path tilt. This paper builds a simulation model of insulators at a voltage level of 220 kV by COMSOL finite element software and analyzes the space electric field distribution characteristics of degraded insulators and the influence of different surface conditions, attitude disturbance, path tilt, etc., on the space electric field distribution of insulators. To reduce the error of UAV detection under complex operating conditions of insulators, a method for detecting the electric field of degraded insulators based on sensitive insulators is proposed and verified by experiments. According to the research results, surface conditions of insulators have little influence on their space electric field, while the attitude disturbance and path tilt of UAVs have a great influence on the electric field of insulators. Sensitive insulators at a level of voltage below 220 kV are generally located at the low-voltage end. The principles of sensitive insulators are combined with the space electric field measurement method to measure the space electric field distribution, thus effectively judging whether there are degraded insulators in the string. The method specified in the paper greatly improves the accuracy and detection efficiency of the contactless electric field detection of insulators, which is of great significance for the promotion of the electric field detection method of insulators in practical applications.

At present, the temperature rise in insulators is observed using infrared thermometry as a common method of diagnosing decay-like insulators. However, the original characteristic data obtained by infrared thermometry cannot effectively distinguish some of the decay-like insulators from those with ageing sheaths. Therefore, it is imperative to find a new diagnostic characteristic quantity. Based on statistical data, this article first explains that existing diagnostic methods have limited diagnostic effectiveness and a high false detection rate for insulators in a slightly heated state. A full-scale temperature rise test is carried out on a batch of composite insulators returned from the field under high-humidity conditions. Two different defective insulators with similar temperature rise profiles are identified, and an electro-thermal coupling simulation model is developed based on the dielectric characteristic parameters of the above insulators for both core rod defects and sheath ageing. A new infrared diagnostic feature, the temperature rise gradient coefficient, is then obtained to identify the source of abnormal heat in insulators using statistical analysis of an infrared image gallery of abnormally hot composite insulators obtained from field inspections and laboratory tests.

This paper investigates the deterioration of, and the abnormal temperature rise in, the GFRP core rod material of compact V-string composite insulators subjected to prolonged alternating flexural loading under wind-induced stresses. The axial stress on the GFRP (Glass Fiber Reinforced Plastic) core rod, resulting from transverse wind loads, is a focal point of examination. By establishing a stress model and damage model, the paper simulates and computes the evolution of damage in the outer arc material of composite insulator core rods subjected to alternating flexural loads. Additionally, a multi-factor coupled aging platform is set up, integrating humidity, heat, and mechanical stress, to simulate the crazing deterioration process of composite insulators under alternating flexural loads. Experimental results reveal that during 400,000 alternating load cycles, the core rod underwent stages of surface damage, damage increasing, fatigue embrittlement, matrix hydrolysis, and fiber fracture. Simultaneously, the silicone rubber sheath on the outer side of the composite insulator’s bending arc develops cracks over aging time, creating pathways for moisture ingress into the interface and core rod. The dielectric constant and dielectric loss factor of the aging region of the core rod increase to varying degrees compared to the non-aging part. Moreover, the degree of abnormal heating of the samples intensifies with the duration of aging experiments. These findings underscore the significance of understanding the aging and decay-like fracture process of compact line V-string composite insulators. They provide crucial insights for future research aimed at enhancing the material properties of composite insulator core rods.

Internal conductive defects in composite insulators severely degrade their insulation performance and are considered concealed defects, posing a significant threat to the safe and stable operation of the power grid. Focusing on this issue, this study develops an electro-thermal multi-physical field simulation model and uses finite element analysis to investigate the electric field distribution and temperature rise characteristics. Composite insulator specimens with varying defect lengths were fabricated using the electrical erosion test. Charged tests were then conducted on these defective specimens, as well as on field-decommissioned specimens. The impact of internal conductive defects on the infrared, ultraviolet, and electric field distribution characteristics of composite insulators during operation was analyzed. The results indicate that the surface electric field of composite insulators with internal conductive defects becomes highly concentrated along the defect path, with a significant increase in electric field strength at the defect’s end. The maximum field strength migrates toward the grounded end as the defect length increases. Conductive defects lead to partial discharge and abnormal temperature rise at the defect’s end and the bending points of the composite insulator. The temperature rise predominantly manifests as “bar-form temperature rise,” with temperature rise regions correlating well with discharge areas. Conductive defects accelerate the decay-like degradation process of composite insulators through a positive feedback loop formed by the coupling of electric field distortion, Joule heating, material degradation, and discharge activity. This study identifies the key characteristics of electrical and temperature rise changes in insulators with conductive defects, reveals the deterioration evolution process and degradation mechanisms of insulators, and provides effective criteria for on-site diagnosis of conductive defects.