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Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The power system stands as a crucial infrastructure pivotal to the country's modern economic, security and social development. This paper addresses challenges in insulator fault detection on power transmission towers, leveraging the advancements in unmanned aerial vehicles equipped with target detection methods. We propose a novel method for insulator defect detection based on YOLOv5 (You Only Look Once), aiming to mitigate the issues associated with high missed detection rates. Small insulator faults and the limitation of unmanned aerial vehicle on-board capacity make it difficult to detect comprehensively. Firstly, the cluster analysis was carried out on the training data to obtain 9 kinds of better preset anchors for insulator detection, which improved the accuracy of the model to identify the location of targets. Secondly, the base-model is used to detect the insulator region, and the detection results are input into the sub-model to detect the location of faults, so as to form a cascade model, and make full use of the advantages of the two models to solve the problem of high missed detection rate. Finally, a lightweight attention module combining channel attention module and spatial attention module is added in YOLOv5 to improve the base-model's attention to insulator region and suppress complex background features. Experimental results show that compared with the original model, the average precision of the proposed method for insulator detection is increased by 6.9%, and the missed detection rate of the fault location is 30% lower. Significant improvements in insulator detection performance have been achieved using the method proposed in this paper. It can not only effectively improve the detection accuracy, but also make the missed detection rate lower to meet the requirements of insulator defect detection and fault warning applications in complex environments, which proves that it has a wide range of application prospects in practice, especially in the field of power industry. [ABSTRACT FROM AUTHOR]

In order to address the problem of poor imaging detection of internal defects caused by the multi-layer curved surface structure and strongly attenuating material of composite insulators, the total focusing method (TFM) with two-layer curved surface correction was investigated, Virtual source (VS) technology was introduced to improve the transmitted energy of the single-element transmission, combined with the delay multiply and sum (DMAS) algorithm to improve the signal-to-noise ratio (SNR) and ultrasonic imaging detection of defects of different sizes of side-drilled holes (SDHs) in the sheath layer and core rod layer. An examination ofthe delamination defects at the core rod layer of the composite insulators was also carried out. The results show that the double-layer surface correction method is able to calibrate the propagation time of the ultrasonic wave to accurately localise the defects. Moreover, the VS technique is able to effectively detect SDI-15 and delamination defects in the core rod layer that cannot be detected using the conventional TFM. After incorporating the DMAS technique, the average SNRs of the TFM and virtual source total focusing method (VSTFM) are improved by 12.75 dB and 13.77 dB, respectively. This shows that the DMAStechnique can significantly improve the SNR of detection. [ABSTRACT FROM AUTHOR]

Composite insulators have been widely used in transmission lines. After being removed from transmission lines, their housing silicone material cannot degrade naturally. To tackle this problem, this paper proposes an effective method to recycle waste insulators by pyrolysis to obtain mullite $(\mathbf{3}\mathbf{Al}_{2}\mathbf{O}_{3}\cdot \mathbf{2}\mathbf{SiO}_{2})$ with high purity and compact structure. The recycling process studied will not generate toxic products. The thermal degradation process of housing material is investigated by analyzing its degradation products including the gas and residues in detail. The experimental results indicate that the colorant agent Fe2O3 inside the housing material is beneficial for the generation of mullite by decreasing the temperature of mullitization. Besides, since the transitional alumina generated by the dehydration of aluminum hydroxide (ATH) has a smaller diameter and can better dissolute into the silica phases, ATH is a better choice as the additional aluminum resource. By comparing the components, structure, and particle size of grains formed at different calcination temperatures, the proposed pyrolysis temperatures of the two stages are 1400°C and 1600°C, respectively.

Composite insulators for high-voltage overhead lines have better performances and are lighter than traditional designs, especially in heavily polluted areas. However, since it is a relatively recent technology, reliable methods to perform live-line diagnostics are still under development, especially with regard to internal defects, which provide few external symptoms. Thermal cameras can be employed, but their use is not always straightforward as the sun radiation can hide the thermal footprint of internal degenerative effects. In this work, an optical E-field sensor has been used to diagnose the internal defects of a set of composite insulators (bandwidth 200 mHz–50 MHz, min. detectable E-field 100 V/m). Moreover, a modelling activity using finite elements has been carried out to identify the possible nature of the defects by comparing experimental E-field profiles with those simulated assuming a specific defect geometry. The results show that the sensor can detect the presence of an internal defect, since its presence distorts the E-field profile when compared to the profile of a sound insulator. Moreover, the measured E-field profiles are compatible with the corresponding simulated ones when a conductive defect is considered. However, it was observed that a defect whose conductivity is not at least two orders of magnitude greater than the conductivity of the surroundings remains undetected. [ABSTRACT FROM AUTHOR]

To study the influence of multi-factors, such as long sunshine, sand erosion, and so on, in southern Xinjiang, we selected two kinds of composite insulators for the transmission lines in southern Xinjiang to study the aging characteristics of the umbrella skirt surface. The results of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) show that the surface roughness of the umbrella skirt is high and there are a large number of micron inorganic particles. The skirt has the characteristics of low C/O element ratio and high Al element content. The results of thermogravimetric analysis and micro infrared test show that the aging depth of the Myli Line skirt after 19 years of operation is 160~190 µm and that of Yuhe Line 1 after 14 years of operation is greater than 180 µm. The plasma discharge method was used to simulate the corona discharge in the actual operation to accelerate the aging of the surface of the umbrella skirt and the hydrophobic recovery of the umbrella skirt was investigated. The results show that the temperature has a great influence on the surface hydrophobic recovery performance after plasma treatment. These results may provide some theoretical guidance and technical support for the selection, operation, and maintenance of composite insulators in Xinjiang. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Optimizing the aerodynamic structure of composite insulators can guarantee the safe operation of power systems. In this study, we construct a simulation model for composite insulator contaminant deposition using the COMSOL simulation software, and the rationality of the simulation model and method is verified through wind tunnel experiments. Taking the FXBW4-110/100 composite insulator as an example, we adopt a progressive optimization plan to explore the impacts of shed spacing s, and shed inclination angles α and β on its contaminant deposition characteristics under DC and AC voltages. Based on the numerical simulation results, we analyze the antifouling performance of insulators before and after structural optimization. The results indicate the following: 1) The contaminant deposition of the insulator under AC and DC voltages is negatively correlated with the shed spacing s, but positively correlated with the lower inclination angle β. 2) Under AC voltages, the contaminant deposition of the insulator increases with the upper inclination angle α, while under DC voltages, the contaminant deposition shows an uptrend first, then a downtrend and then an uptrend again with the increase of the upper inclination angle α. 3) Compared with the original model, the AC-optimized model ( α = 6°, β = 2° and s = 98 mm) with a larger shed spacing s, and smaller shed inclination angles α and β showed superior antifouling performance at wind speeds of no less than 2 m/s, and under the typical conditions ( v = 2.5 m/s, d = 20 μm, and ρ = 2 200 kg/m 3), its contaminant deposition is 15% less than that of the original model ( α = 10°, β = 2° and s = 80 mm).

Composite insulators have excellent performance and are more and more widely used in power grid. The performance of composite insulators with different service duration will decline in varying degrees, which could pose a threat to the safe operation of power grid. Multiple composite insulators were collected from the northern region of China after operation to study the effects of electric field strength, pollution level, and service life on aging characteristics. The changes in hydrophobicity, mechanical properties, and material properties of the umbrella shed during aging are obtained through multiple experiments. The mechanism of performance degradation is revealed from the perspective of molecular structure through microscopic test. The molecular dynamics simulation shows the process of molecular bond breaking and morphological changes, revealing the principle of viscoelastic changes. The results reveal that the performance of insulator shed gradually declines with the increase in service life. The hydrophobicity and hardness of high-voltage end shed are similar to that of middle section shed, while other parameters are obviously different, indicating that the electric field can aggravate the aging. FTIR results show that the main chain and hydrophobic side chain of silicone rubber are destroyed. XPS and SEM results show that the crosslinking degree of silicone rubber increases and the porosity increases. The molecular simulation of silicone rubber shows that its morphology gradually changes to tension and its stiffness decreases during bond breaking degradation. The above changes in the microstructure of silicone rubber lead to the decline of insulator performance. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of surface pollution on abnormal heating with 110kV composite insulators as the research subject. Firstly, infrared inspections were conducted on three full-sized composite insulators at various pollution classes, and the infrared spectrum characteristics of contaminated composite insulators were analyzed. Subsequently, water absorption experiments were performed on silicone rubber flat samples to analyze the effects of pollution on insulator moisture absorption properties and dielectric performance. Finally, tests were conducted on short samples with protective sheaths of six levels of pollution classes in an artificial climate chamber to analyze the influence of leakage current on temperature rise and to assess the impact of pollution on the surface electric field distribution of insulators using the finite element method. The research results indicated that pollution caused and exacerbated abnormal heating in composite insulators. In a high-humidity environment, when the pollution level of full-sized samples exceeded class B, the heating temperature of insulator exceeded 0.5 ℃. Pollution had a more significant impact on the aging of the composite insulator materials; polluted composite insulators exhibited a 'U'-shaped distribution pattern of the surface electric field, with the heating region primarily concentrated in the high-field strength area of the end sheath. The wet pollution state had a significant impact on the electric field of composite insulators, with the maximum electric field strength increasing from the original 4.8 kV/cm to 6.2 kV/cm. The primary cause of abnormal temperature rise in polluted composite insulators was the polarization loss generated by the sheath and the absorption of moisture by pollution, with surface resistive leakage current having a relatively minor influence. This study can serve as a theoretical reference for online infrared diagnostics and the mitigation of abnormal heating issues in polluted composite insulators. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to study the cause of wire falling accident caused by fracture of 500 kV composite insulator in the no-fly zone of a province， various inspections and tests were carried out on the accident insulator string according to the current standard. The results of comprehensive detection and analysis and on-site fault investigation show that due to the defects in the interface between the glass fiber and the silicone rubber sheath of the composite insulator rod， the rod of the insulator is aged after many years of operation. In addition， due to the comprehensive influence of the operating environment， the internal fibrosis and overall structural degeneration of the rod are aggravated， which eventually causes the insulator to break down and cause the wire to fall off. Finally， in order to avoid the recurrence of such accidents and ensure the safe and stable operation of the power grid， the operation and maintenance strategy of composite insulators is given for the lines under the jurisdiction of the UAV no-fly zone and weak signal zone.

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming to solve the partial discharge problem caused by defects in composite insulators, most existing live detection methods are limited by the subjectivity of human judgment, the difficulty of effective quantification, and the use of a single detection method. Therefore, a composite insulator defect diagnosis model based on acoustic–electric feature fusion and a multi-scale perception multi-input of stacked auto-encoder (MMSAE) network is proposed in this paper. Initially, during the withstanding voltage experiment, the electromagnetic wave spectrometer and ultrasonic detector were used to collect and process the data of six types of composite insulator samples with artificial defects. The electromagnetic wave spectrum, ultrasonic power spectral density, and n-S map were then obtained. Then, the network architecture of MMSAE was built by integrating a stacked auto-encoder and multi-scale perception module; the feature extraction and fusion methods of the electromagnetic wave spectrum and ultrasonic signal were investigated. The proposed method was used to diagnose test samples, and the diagnostic results were compared to those obtained using a single input source and the artificial neural network (ANN) method. The results demonstrate that the detection accuracy of acoustic–electric feature fusion is greater than that of a single feature; the accuracy of the proposed method is 99.17%, which is significantly higher than the accuracy of the conventional ANN method. Finally, composite insulator defect diagnosis software based on PYQT5 and Keras was developed. Ten 500 kV aging composite insulators were used to validate the effectiveness of the proposed method and design software. [ABSTRACT FROM AUTHOR]

The abnormal heating of composite insulators on transmission lines frequently occurs, seriously threatening the power grid's safe and stable operation. For different types of abnormal heating composite insulators, undifferentiated replacement wastes a lot of labor and material resources. This study explores the abnormal heating composite insulators under different environmental humidity and wind speed conditions. The heating and discharge of composite insulators are observed, and the heating range, heating shape, and temperature rise (ΔT) are analyzed. The abnormal heating of the sheath-aging composite insulator is related to the aging of the silicone rubber and the environmental humidity. The partial discharge caused by the core rod's defect is the primary source of the temperature rise in the decay-like insulator. The heating range of the contaminated insulator is connected to the environmental humidity, and the ΔT increases with the salt density. The ΔT and heating range of the three types of abnormal heating increase with the ambient humidity. The heating phenomenon under low humidity is an important characteristic that distinguishes decay-like and contaminated insulators from sheath-aging insulators. Therefore, the on-site infrared inspection should be carried out in sunny and windless weather to prevent the impact of high humidity and wind speed on infrared temperature measurement. [ABSTRACT FROM AUTHOR]

Internal discharges in composite insulators often cause abnormal heating, interface failure and erosion of the core rod. However, the mechanism and the exact process of the degradation of HTV shed and FRP core rod caused by internal discharges are still unclear. In this work, abnormal heating insulator samples are taken from an AC 500 kV extra-high voltage (EHV) transmission line. Macro- and micro-scopic morphological observation, hardness tests, industrial CT tests and chemical property tests are applied on the samples. The cause of heating and the deterioration mechanism of each part of insulators is further explored. Cavities and air holes are found in the HTV skirts in this batch of insulators, which are generated during manufacturing. These cavities lead to the distortion of electrical field and become the origin of the discharges. Decomposition of polydimethylsiloxane leads to the hardening and chalking of the HTV shed. It is also found that the adhesive in the rod-housing interface fails during operation. Epoxy resin in core rod decomposes in a multi-factor aging environment, leading to the decay-like aging of the core rod surface. As the aging progress develops inward, the insulator will eventually lose its mechanical properties. It is inferred that the internal discharge is the main reason of heating and deterioration of composite insulators. Moreover, long-term discharge will lead to the decay-like aging of core rods.

The increase in bird populations along the Hexi Corridor has led to an increase in flashover faults on 330 kV transmission lines caused by bird droppings. To mitigate the issue of line tripping caused by bird droppings, it is necessary to analyze the distribution of the electric field near composite insulators during the process of bird droppings falling. A three-dimensional model, including the tower, bird droppings, and insulators, was created to assess the impact of bird droppings’ characteristics on the electric field near the insulators. Based on simulation results, a bird-proof cover was designed to modify the trajectory of the bird droppings’ path. The research found that when bird droppings are grounded and continuous, the most severe distortion of the residual air gap field occurs at a distance of 599.34 mm from the insulator axis. In the dynamic process of ungrounded and continuous bird droppings falling downward with a length less than 3200 mm, the electric field intensity in the residual air gap remains below 5.66 kV/cm outside the circular area centered at the insulator skirt with a radius of 740 mm. Based on the simulation results under both single-end grounded and ungrounded conditions of bird droppings, a bird-proof cover structure was devised to alter the location where bird droppings fall. After bird droppings fall along the edges of the bird-proof cover, the average electric field intensity between the bird droppings and the high-voltage terminal is maintained below 3.02 kV/cm. These research findings lay the foundation for subsequent fabrication of physical models of bird-proof covers.

Silicone rubber housings crack under the combined internal and external factors and expose the core rod. The exposed core rod deteriorates or breaks under electric fields and electrical current. Based on the main characteristics and mechanism of the core rod corrosion, this paper performs an electrical erosion test in an acid-fog environment and analyzes the core rod's macroscopic results and physicochemical properties. The results indicate the following. First, the discharge on core rod during the electrical erosion process contains four consecutive stages. The electrical current, partial discharge, temperature increase, and macroscopic morphology show regular changes at different stages. The arc usually occurs in the carbonization channel, making the channel have the maximum heat. The area of the core rod heating constantly changes but mainly at the high-voltage side and presents as a regional temperature increase. Second, the fracture of glass fiber and ablation of epoxy resin matrix are related to the continuous action of nitric acid. The generation, expansion, and release of pyrolysis gas form bubbles and pores on the epoxy resin matrix. Erosion and pyrolysis cause the loss of the epoxy resin matrix. Third, the combined effect of electrical current, nitric acid, and heat damage the core rod axially and radially. The study provides support for the subsequent core rod deterioration and fracture mechanism.

Composite insulators for high-voltage overhead lines have better performances and are lighter than traditional designs, especially in heavily polluted areas. However, since it is a relatively recent technology, reliable methods to perform live-line diagnostics are still under development, especially with regard to internal defects, which provide few external symptoms. Thermal cameras can be employed, but their use is not always straightforward as the sun radiation can hide the thermal footprint of internal degenerative effects. In this work, an optical E-field sensor has been used to diagnose the internal defects of a set of composite insulators (bandwidth 200 mHz–50 MHz, min. detectable E-field 100 V/m). Moreover, a modelling activity using finite elements has been carried out to identify the possible nature of the defects by comparing experimental E-field profiles with those simulated assuming a specific defect geometry. The results show that the sensor can detect the presence of an internal defect, since its presence distorts the E-field profile when compared to the profile of a sound insulator. Moreover, the measured E-field profiles are compatible with the corresponding simulated ones when a conductive defect is considered. However, it was observed that a defect whose conductivity is not at least two orders of magnitude greater than the conductivity of the surroundings remains undetected.

To study the influence of multi-factors, such as long sunshine, sand erosion, and so on, in southern Xinjiang, we selected two kinds of composite insulators for the transmission lines in southern Xinjiang to study the aging characteristics of the umbrella skirt surface. The results of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) show that the surface roughness of the umbrella skirt is high and there are a large number of micron inorganic particles. The skirt has the characteristics of low C/O element ratio and high Al element content. The results of thermogravimetric analysis and micro infrared test show that the aging depth of the Myli Line skirt after 19 years of operation is 160~190 µm and that of Yuhe Line 1 after 14 years of operation is greater than 180 µm. The plasma discharge method was used to simulate the corona discharge in the actual operation to accelerate the aging of the surface of the umbrella skirt and the hydrophobic recovery of the umbrella skirt was investigated. The results show that the temperature has a great influence on the surface hydrophobic recovery performance after plasma treatment. These results may provide some theoretical guidance and technical support for the selection, operation, and maintenance of composite insulators in Xinjiang.

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.

Composite insulator is widely used in power system, it is of great significance to study the contamination performances and influence factors of composite insulator to reduce the occurrence of insulator pollution flashover accidents. Based on FXBW4-10 / 100 composite insulator, then a Eulerian multiphase flow simulation model of insulator was founded to analyze the contamination performances of insulator surface under different wind speeds, particle sizes and concentration. The results show that the pollution particles are mainly concentrated on the windward side and leeward side of the insulator, with less pollution on the crossward side of the insulator. The contamination volume fraction on the buttom surface is higher than that on the top surface. With the increase of wind speed, the contamination volume fraction on the windward and leeward side of the insulator are gradually increases, and the contamination volume fraction on the crosswind side increases first and then decreases. The contamination degree of insulator surface increases linearly with the increase of particle concentration, and the whole contamination distribution is Umbrella-shaped. The contamination degree on the leeward side increases first and then decreases with the increase of particle size. [ABSTRACT FROM AUTHOR]

In this study, an optimized unilateral magnetic resonance sensor with a three-magnet array is presented for assessing the aging of composite insulators in power grids. The sensor's optimization involved enhancing the static magnetic field strength and the homogeneity of the RF field while maintaining a constant gradient in the direction of the vertical sensor surface and maximizing homogeneity in the horizontal direction. The center layer of the target area was positioned 4 mm from the coil's upper surface, resulting in a magnetic field strength of 139.74 mT at the center point of the area, with a gradient of 2.318 T/m and a corresponding hydrogen atomic nuclear magnetic resonance frequency of 5.95 MHz. The magnetic field uniformity over a 10 mm × 10 mm range on the plane was 0.75%. The sensor measured 120 mm × 130.5 mm × 76 mm and weighed 7.5 kg. Employing the optimized sensor, magnetic resonance assessment experiments were conducted on composite insulator samples utilizing the CPMG (Carr–Purcell–Meiboom–Gill) pulse sequence. The T2 distribution provided visualizations of the T2 decay in insulator samples with different degrees of aging. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The anti-pollution flashover characteristic of composite insulators is the main indicators to evaluate their electrical performance, and the pollution flashover voltage can directly characterize the anti-pollution flashover characteristics of the insulators. This paper proposed an on-line detection method for the pollution flashover voltage of composite insulators. Samples of composite insulator shed with different hydrophobicity were prepared by using NaOH solution with pH value of 13 and temperature of 80 °C. According to the distribution of water droplets on the surface of the sample, the characteristic parameter of the number of water droplets was proposed. The samples with different characteristic parameters were smear-stained and used for the pollution flashover voltage test. The relationships between the number of water droplets on the sample surface and the pollution flashover voltage and leakage current were obtained, which can provide guidance for the evaluation of the operation state of composite insulators.

Suspension line insulators are during their operation subject to static forces and variable loads, usually of a cyclic character. These variable loads have a significant impact on the mechanical durability of composite insulators. A method of providing durability forecast for composite line insulators based on fatigue characteristics has been proposed. The method allows providing durability forecast of insulators in a wide range of variable loadings, i.e. from quasi-static to high amplitude loadings.

In order to explore the relationship between glued flange joint damage and the change of dynamic characteristics of composite insulator bushing， the paper takes a ± 800 kV composite insulator as the research object and establishes the finite element model of insulator. Moreover， it presets the damage influence factors in colloid height and angle direction and calculates the dynamic characteristics of composite insulators before and after damage. The results show that the crack and deformation of the adhesive layer interface at the flange joints of composite insulators may reduce the overall structural stiffness. The decrease of the flange joint’s bending stiffness is linear with the flange’s cracking area in colloid height and angle direction. The decreased cracking area of the colloid in the height direction of the flange angle is also approximately linear with the reduced bending stiffness area of the flange joint. The colloid damage in the vibration direction has the most significant impact on the flange stiffness.

Composite insulators have gradually become the preferred approach for electrical insulation in power systems, especially in polluted areas. Composite insulators consist of three main components: the shed, rod, and end fitting. Insulators withstand mechanical stresses via rods that are composed of glass-fiber-reinforced epoxy (GFRE). However, regardless of the high tensile strength of GFRE rods, in real-life operation, abnormal fractures have frequently been reported all over the world, which substantially increase the risk of major accidents in power systems. Fractural accidents mainly consist of brittle and decay-like fractures, which exhibit rather different morphologies at the cross sections. Brittle fracture has been effectively eliminated, while the mechanism of decay-like fracture has still not been clearly revealed. In this study, surface discharge tests were applied to investigate the discharge influence on the degradation of GFRE. The test successfully simulated the composition variation of the rods in real-life composite insulators with decay-like fractures. Moreover, it confirmed that the distinction between the characteristics of brittle fracture and decay-like fracture stems from epoxy degradation due to hydrolysis and carbonization. In addition, the respective influences of the resin type, glass fiber type, and acid liquid immersion on the degradation process were probed, and the degradation mechanism proposed in this research was verified. Based on the results, measures for preventing the development of decay-like fractures in real-life operations were determined. [ABSTRACT FROM AUTHOR]

Insulators and auxiliary equipment are used to provide electrical isolation in energy transmission. The high electric field distribution on the composite insulators causes a decrease in the hydrophobicity and increases the aging of the insulator over time. Corona rings are used to balance the electric field distribution with insulators. The corona rings used are designed according to thickness, diameter, and height parameters. In this study, the design parameters of the corona ring used in composite insulators are evaluated by finite element analysis. In this context, different types of corona rings were modeled in real scale in the computer environment and transferred to the Ansys Electronics Suite finite element software program. Analyses were performed with appropriate analysis settings and material definitions. Different design parameters were examined in the analysis, and the results were interpreted and shown in detail in the article. As a result, the necessity of system evaluation with finite element analyses in designing insulation systems used in energy transmission has been demonstrated. [ABSTRACT FROM AUTHOR]

To be able to predict the DC flashover characteristics of composite insulators, a four-layer BP neural network model is established with composite insulator shed structure parameters as the input. Three algorithms (gradient descent with momentum, RMSProp gradient descent, and Adam gradient descent) are applied, and the DC pollution flashover experimental data of composite insulators are used as training data. The results show that all three algorithms have good prediction capabilities. Among them, the Adam gradient descent model has the best prediction result, which can make the average prediction with an error of less than 4% and a maximum error of less than 8%, so these results can provide a reference for the design of composite insulators in DC voltage and product performance verifications. [ABSTRACT FROM AUTHOR]

When the silicone rubber composite insulator is exposed outdoors for a long time, it will be affected by high‐temperature ultraviolet environments. In order to ensure the operation of silicone rubber composite insulators, a super‐hydrophobic composite insulator with antiaging characteristics was prepared by mixing cerium dioxide (CeO2) with silicone rubber and spraying CeO2 on the surface of silicone rubber. This article studied the aging characteristics of the base and surface of silicone rubber composite insulator by CeO2 in ultraviolet environment. The properties of silicone rubber composite insulators before and after aging were tested by mechanics, contact Angle, rolling Angle, bounce, and icing experiments. The aging mechanism of silicone rubber was analyzed by Fourier transform infrared spectroscopy and search engine marketing. This study prepared composite insulators with excellent mechanical, hydrophobic, and antiicing properties. The aging resistance of silicone rubber composite insulators is improved by adding CeO2 into silicone rubber matrix and spraying CeO2 on the surface, which also ensure the use of composite insulators in high‐temperature ultraviolet environment. [ABSTRACT FROM AUTHOR]

In this study, the aging process of composite insulator silicone rubber in a mountainous region environment was studied and a lifespan prediction model was constructed. Silicone rubber samples with various exposure times were analyzed based on the microstructure, physical properties, functional groups, and chemical environment of silicon. All experimental results corresponded to three aging stages: platform stage, upturn stage, and acceleration stage. Based on linear regression method, the peak content of Si(-O)2 and shore hardness A were selected to establish the lifespan prediction model for silicone rubber. Verification of the model showed that the residual lifespan error is less than 1.5 years. This study is based on a systematic analysis of three stages of the aging process for silicone rubber in composite insulators and obtaining critical aging parameters. Furthermore, a lifespan prediction model is proposed and validated.