Search Results (30)

In wildfire environments, high temperatures generated by wildfires may cause thermal aging, deformation, and even burning damage to the silicone rubber sheds of composite insulators, thereby deteriorating their surface hydrophobicity and insulation characteristics. Meanwhile, ash and carbonaceous particles produced by vegetation combustion tend to accumulate on insulator surfaces, forming conductive contamination layers that reduce surface resistance, intensify leakage current activity, and increase the risk of flashover. To investigate these effects, FXBW₄-35/70 composite insulators were selected as the research object. A simulated burning test platform was established to evaluate variations in the mechanical properties of insulator sheds under wildfire conditions. In addition, the feasibility of using simulated ash was assessed. AC flashover tests were conducted on contaminated insulators to quantify the influence of ash deposition on flashover performance. Beyond confirming the thermal aging behavior of silicone rubber under wildfire exposure, this study establishes a quantitative relationship between wildfire ash deposition, equivalent contamination severity, and flashover performance. A correction model for post-fire pollution withstand voltage is further proposed, providing a practical basis for condition assessment and maintenance of transmission line insulators after wildfire events. Full article

Silicone rubber is an important external insulating material for composite bushings, composite insulators, and other power equipment. During long-term service, it is inevitably exposed to coupled environmental and electrical stresses, such as elevated temperature, moisture ingress, strong electric fields, and partial discharge, which may lead to hydrophobicity loss, surface chalking, crack propagation, and particle shedding. To reveal the microscopic degradation mechanism of silicone rubber under complex operating conditions, a molecular model of methyl vinyl silicone rubber was constructed using Materials Studio. A stable silicone rubber molecular structure was obtained through crosslinking, geometry optimization, and ensemble relaxation. Subsequently, a reactive molecular dynamics simulation system under coupled temperature–humidity–electric field conditions was established using LAMMPS and the ReaxFF reactive force field. Different temperature gradients, electric field intensities, and aging–recovery stages were designed to investigate the degradation behavior of silicone rubber. The evolution of the maximum carbon content, maximum silicon content, carbon-containing decomposition products, and typical small-molecule products, including H₂, H₂O, CH₄, C₂H₂, C₂H₄, and C₂H₆, was statistically analyzed. In addition, atomic trajectory tracking was performed to clarify the processes of methyl group detachment, Si-O bond cleavage, water molecule participation, and molecular chain reconstruction. The results show that high temperature mainly promotes methyl group detachment from side chains and fracture of the siloxane main chain, while a strong electric field accelerates the decomposition process and induces the transformation of long siloxane chains into shorter chains. Water molecules can react with broken siloxane chains to form hydroxyl-containing structures, making the structural degradation partially irreversible. The degradation process of silicone rubber under coupled temperature–humidity–electric field stress can be summarized as side-chain detachment, main-chain scission, water-assisted reactions, free-radical recombination, and local molecular aggregation. This study provides a molecular-level theoretical basis for aging mechanism analysis, condition assessment, and lifetime prediction of composite external insulating materials. Full article

To investigate the aging behavior of high-temperature-vulcanized silicone rubber (HTV-SiR) used in composite insulator sheds under coupled electrical, thermal, humidity, and mechanical stresses, accelerated aging tests were conducted to emulate the service conditions of ±800 kV ultra-high-voltage direct current (UHVDC) systems in Guangzhou, China. The physicochemical, mechanical, and electrical properties of the specimens were systematically characterized. The results show simultaneous degradation of both electrical and mechanical performance. In particular, the tensile strength exhibits a significant monotonic decrease and drops to 49.52% of its initial value under the most severe condition (0.5 kV·mm⁻¹ and 5% tensile strain) after 75 days. In contrast, the DC breakdown strength shows a non-monotonic “rise-then-fall” trend and decreases more markedly with increasing tensile strain. To address the one-shot and destructive nature of tensile testing and the associated statistical uncertainties, a lifetime prediction framework was developed by integrating a generalized Eyring acceleration relation with a stochastic degradation process. Under representative service conditions of 0.09 kV·mm⁻¹ and 0.2% tensile strain, the predicted lifetimes corresponding to failure probabilities of 10%, 75%, and 90% are 1.77, 9.08, and 17.90 years, respectively. The applicability of the model is supported by field-aged specimens. These findings provide a mechanistically grounded and reliability-oriented basis for condition assessment, lifetime-margin evaluation, material screening, and maintenance planning of UHVDC composite insulators operating in hot–humid environments. Full article

During the long-term operation of composite insulators in transmission lines, they are easily affected by harsh environments, resulting in hidden defects such as surface contamination, shed damage, and adhesive failure. A defect detection method based on microwave for composite insulators was proposed, and a corresponding numerical simulation model was established. A large-aperture horn antenna model with a wide frequency band and high gain was built, the accuracy of which was verified. In the simulation, shed crack defects were selected as representative probes to model typical defects in the sheds, sheath, and core rod of composite insulators. This study investigated defects with varying severity levels and spatial distributions while also exploring optimal placement configurations for detection antennas. An experimental platform was built for testing, and it was found that the experimental results showed a similar changing trend to the simulation results, which further verified the accuracy of the simulation model and the feasibility of simulating defects. Full article

Optical fiber composite insulators are essential for photoelectric current measurement, yet insulation failure at embedded optical fiber interfaces remains a major challenge to long-term stability. This study proposes a strategy to replace conventional silicone rubber with cycloaliphatic-like epoxy resin (CEP) as the shed-sheathing material. Three optical fibers with distinct outer coatings, ethylene-tetrafluoroethylene copolymer (ETFE), thermoplastic polyester elastomer (TPEE), and epoxy acrylate resin (EA), were evaluated for their interfacial compatibility with CEP. ETFE, with low surface energy and weak polarity, exhibited poor wettability with CEP, resulting in an interfacial tensile strength of 0 MPa, pronounced dye penetration, and rapid electrical tree propagation. Its average interfacial breakdown voltage was only 8 kV, and the interfacial leakage current reached 35 μA after hygrothermal aging. In contrast, TPEE exhibited high surface energy and strong polarity, enabling strong bonding with CEP, yielding an average interfacial tensile strength of approximately 46 MPa. Such a strong interface effectively suppressed electrical tree growth, increased the average interfacial breakdown voltage to 27 kV, and maintained the interfacial leakage current below 5 μA even after hygrothermal aging. EA exhibited moderate interfacial performance. Mechanism analysis revealed that polar ester and ether groups in TPEE enhanced interfacial electrostatic interactions, restricted the mobility of CEP molecular chain segments, and increased charge traps. These synergistic effects suppressed interfacial charge transport and improved insulation strength. This work offers valuable insight into structure–property relationships at fiber–resin interfaces and provides a useful reference for the design of composite insulation materials. Full article

In high-voltage transmission lines, insulators subjected to prolonged electromechanical stress are prone to zero-value defects, leading to insulation failure and posing significant risks to power grid reliability. The conventional detection method of spark gap is vulnerable to environmental interference, while the emerging electric field distribution-based techniques require complex instrumentation, limiting its applications in scenes of complex structures and atop tower climbing. To address these challenges, this study proposes an electroluminescent sensing strategy for zero-value insulator identification based on the electroluminescence of ZnS:Cu. Based on the stimulation of electrical stress, real-time monitoring of the health status of insulators was achieved by applying the composite of epoxy and ZnS:Cu onto the connection area between the insulator steel cap and the shed. Experimental results demonstrate that healthy insulators exhibit characteristic luminescence, whereas zero-value insulators show no luminescence due to a reduced drop in electrical potential. Compared with conventional detection methods requiring access of electric signals, such non-contact optical detection method offers high fault-recognition accuracy and real-time response capability within milliseconds. This work establishes a novel intelligent sensing paradigm for visualized condition monitoring of electrical equipment, demonstrating significant potential for fault diagnosis in advanced power systems. Full article

To investigate the force characteristics of phase spacers during ice-shedding galloping of transmission lines, a comprehensive finite element model for double-circuit lines on the same tower was developed. The analysis focused on the spacers’ suppression effect on galloping and the variation in their axial force. A solid finite element model of phase spacers was constructed, incorporating suspension fittings, ball eye links, and composite insulators. By using the axial force time history under galloping as excitation, the deformation and stress distribution of phase spacers, as well as stress changes in their connection fittings, were studied. The results revealed that phase spacers significantly suppress galloping, with a more pronounced effect on middle-phase conductors. Axial force fluctuates sharply due to galloping, but stabilizes over time, approaching a limit value. The ice-shedding galloping phenomenon impacts stress distribution, with the ball eye link being more susceptible to fracture. Although the ball-and-socket connection at the composite insulator stem may experience high bending stress, the overall stress distribution meets safety requirements, ensuring safe and stable transmission line operation. Full article

Icing significantly reduces the electrical performance of insulators, and grid failures caused by insulator icing are common. Currently, most research on the flashover characteristics of insulators under icing conditions focuses on artificially iced suspension insulators, with limited studies on post insulators under natural icing conditions. The shed spacing of post insulators is smaller, making them more prone to bridging by icicles in the same icing environment, which exacerbates insulation problems. Therefore, investigating the icing characteristics of post insulators is crucial. In this study, natural icing growth was observed on seven different types of post insulators at the Xuefeng Mountain Energy Equipment Safety National Observation and Research Station. The icing morphology and characteristics of these insulators were examined. The main conclusions are as follows: (1) the icing type and morphology of post insulators are influenced by meteorological conditions, with more severe icing observed on the windward side. (2) The icing mass and icicle length of the insulator increase nonlinearly with icing time. Specifically, during the glaze icing period from 0 to 8 h, the ice mass on the Type V composite post insulator was 3.89 times greater than that during the 13-to-18 h period. (3) Within the same icing cycle, the icing growth rate on composite post insulators is faster than on porcelain post insulators. (4) Compared to suspension insulators, the sheds of post insulators are more easily bridged by icicles. Notably, when the sheds of post insulators are bridged by icicles, the length of icicles on suspension insulators is only half of the gap size. Full article

Composite insulators have been widely used in power grids due to their excellent electrical-external-insulation performance. Long-term operation at high voltage levels accelerates the aging of composite insulators; however, there is a scarcity of research on aged composite insulators operating at 500 kV for over ten years. In this paper, the mechanical, electrical, and microscopic properties were tested on different sheds along a 500 kV composite insulator that had been running for 18 years. Additionally, the results were compared with a new insulator and the standards for live insulator operation. The results showed that the aging of the high-voltage end of composite insulators was the most serious. The results of the physical properties test indicated that the insulator’s hardness was compliant but its tensile strength and break elongation did not meet standards. Under wet conditions, the pollution flashover voltage decreases by about 50% compared to the new insulator. Combined with the microscopic test results, the shed skeleton structure could be damaged and the filler might be lost during the aging process of polydimethylsiloxane (PDMS). The hardness of the insulator would increase by the precipitation of inorganic silicon; however, inorganic silicon might destroy the hydrophobicity and other properties of insulator sheds. These results can provide theoretical references for insulator life prediction and operation protection. Full article

This study delves into the integration of phase change materials (PCM) in solar thermal collector systems to address this challenge. By incorporating nano encapsulated PCMs, researchers have mitigated concerns surrounding PCM leakage, revolutionizing the potential of solar collector systems to elevate energy efficiency, diminish carbon emissions, and yield manifold benefits. This article comprehensively investigates the design and utilization of solar phase change energy storage devices and examines the transformative impact of employing nano-coated phase change materials (Nano capsules) to augment solar collector performance. The integration of paraffin-based PCM and the insulation of the collector system have been crucial in optimizing heat retention and operational efficacy. The composition of the PCM involves a balanced blend of octadecane phase-change particles and water as the base fluid, designed to maximize thermal performance. Analysis of the experimental findings demonstrates the dynamic thermal behavior of the nano encapsulated phase change material, revealing distinctive temperature profiles about fluid dynamics and absorbent characteristics. Notably, the study emphasizes the nuanced trade-offs associated with the conductivity and melting temperature of the Nano encapsulated PCM, yielding valuable insights into energy storage capacity limitations and thermal performance variations throughout diurnal cycles. Central to the investigation, the optimal nanoparticle proportion is elucidated, shedding light on its pivotal role in modulating PCM performance. Furthermore, findings underscore the complex interplay between nanoparticle volume fraction and thermal fluid temperature, providing critical perspectives on optimizing PCM-enhanced solar collector systems. Full article

Copper oxide nanowires (NWs) are promising elements for the realization of a wide range of devices for low-power electronics, gas sensors, and energy storage applications, due to their high aspect ratio, low environmental impact, and cost-effective manufacturing. Here, we report on the electrical and thermal properties of copper oxide NWs synthetized through thermal growth directly on copper foil. Structural characterization revealed that the growth process resulted in the formation of vertically aligned NWs on the Cu growth substrate, while the investigation of chemical composition revealed that the NWs were composed of CuO rather than Cu₂O. The electrical characterization of single-NW-based devices, in which single NWs were contacted by Cu electrodes, revealed that the NWs were characterized by a conductivity of 7.6 × 10⁻² S∙cm⁻¹. The effect of the metal–insulator interface at the NW–electrode contact was analyzed by comparing characterizations in two-terminal and four-terminal configurations. The effective thermal conductivity of single CuO NWs placed on a substrate was measured using Scanning Thermal Microscopy (SThM), providing a value of 2.6 W∙m⁻¹∙K⁻¹, and using a simple Finite Difference model, an estimate for the thermal conductivity of the nanowire itself was obtained as 3.1 W∙m⁻¹∙K⁻¹. By shedding new light on the electrical and thermal properties of single CuO NWs, these results can be exploited for the rational design of a wide range of optoelectronic devices based on NWs. Full article

Energy conservation has emerged as a strategic target worldwide, which will enable the protection of the environment and the preservation of natural resources. Energy consumption in buildings for heating and cooling is considered one of the main sources of energy consumption in several countries. For this reason, there is an ongoing search for appropriate alternatives to preserve energy and reduce energy losses. To overcome this challenge, thermal insulation is becoming increasingly essential to save energy. Although a large number of insulation materials are used commercially, this sector still faces various challenges such as cost, thermal and mechanical properties, the end-of-life cycle, as well as health issues, etc. Furthermore, the harmful impact of buildings on the environment and health issues should be considered not only in relation to the energy expended whilst using them but also in relation to the energy performance materials they are constructed from. The insulation materials commonly used in the construction industry today are polymer-based materials such as polystyrene and polyurethane foam. These materials have a critical impact on the environment. In light of these results, several researchers have concluded that it is imperative to develop insulating materials with outstanding properties that have a lower impact on the environment and are relatively affordable. Agricultural and/or industrial wastes, and even natural fibers, are increasingly used as green insulation materials, as they are an eco-friendly, cost-effective alternative to conventional oil-based materials, as well as the fact that their end-of-life cycle does not pose a critical problem. This review paper discusses the several renewable resources and industrial wastes developed as thermal insulations. Furthermore, it sheds light on composite materials used as construction materials, as well as their end-of-life cycle. Full article

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. Full article

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. Full article

The thermal radiation phenomenon is more crucial than other thermal transportation phenomena at elevated temperatures (>300 °C). Therefore, infrared radiation resistance and its performance on thermal conduction of nanofibrous aerogel with Titanium oxide (TiO₂) filler have been investigated compared to control groups (silica nanofibrous aerogels with and without filler). Nanofibrous aerogel has been produced by electrospun silica nanofibers. Later, TiO₂ opacifier and a non-opacifier filled materials were prepared by a solution homogenization method and then freeze-dried to obtain particle-filled nanofibrous aerogel. Moreover, the thermal radiation conductivity of the composite was calculated by numerical simulation, and the effect of the anti-infrared radiation of the TiO₂ opacifier was obtained. The fascinating inhibited infrared radiation transmission performance (infrared transmittance ~67% at 3 μm) and excellent thermal insulation effect (thermal conductivity of 0.019 Wm⁻¹K⁻¹ at room temperature) and maximum compressive strengths (3.22 kPa) of silica nanofibrous aerogel with TiO₂ opacifier were verified. Excellent thermal insulation, compression and thermal stability properties show its potential for practical application in industrial production. The successful synthesis of this material may shed light on the development of other insulative ceramic aerogels. Full article