Search Results (1,938)

With the demand for high-voltage electrical insulation systems increasing, the development of environmentally friendly anti-corona materials with reliable nonlinear electrical properties has become essential. In this work, a waterborne polyurethane/epoxy (WPU/EP) composite coating was fabricated using micron-sized SiC (α-SiC), nano-sized SiC (β-SiC), and n-ZnO as multi-scale fillers. Its microstructure, nonlinear conductivity, flashover characteristics, and electro-thermal aging performance were systematically investigated. The results indicate that the incorporation of α-SiC significantly enhances conductivity under high electric fields by forming conductive pathways, while β-SiC further improves nonlinear behavior through interfacial bridging effects. The addition of n-ZnO modifies interfacial characteristics and contributes to improved electrical response. Moreover, the flashover performance is strongly dependent on filler composition, showing a critical role of nano-fillers in charge trapping and transport regulation. Electro-thermal aging tests on simulated stator bars reveal that the developed coating exhibits improved resistance to degradation compared with conventional materials. These findings demonstrate the effectiveness of multi-scale filler design in tailoring the electrical and insulation performance of waterborne anti-corona coatings. Full article

This study aimed to describe the endocrine, cellular, and transcriptomic changes associated with mild heat stress responses in Wugu-Hu and Hu rams. Testicular samples from rams exposed to 3 days of scrotal insulation, resulting in an approximate 3 °C increase in scrotal temperature, and corresponding controls were analyzed for endocrine activity, seminiferous tubule morphology, germ cell composition, and transcriptomic profiles. There were no significant changes in testosterone, follicle-stimulating hormone, or luteinizing hormone after 3 days of mild heat exposure in either breed. Wugu-Hu rams showed greater disorganization of seminiferous tubules. Apoptotic events occurred mainly from spermatocytes to spermatids and were accompanied by a greater decline in spermatids in Wugu-Hu rams. Comparative transcriptomic analysis between Wugu-Hu and Hu rams identified 854 differentially expressed genes, mainly enriched in immune response function. We conclude that scrotal heat stress does not disrupt endocrine balance at the level applied in this study, but it induces breed-dependent morphological and testicular cellular responses. The differences in the immune response of Hu and Wugu-Hu rams may contribute to their distinct levels of spermatocytes and spermatids’ response to elevated temperatures. Full article

This study addresses the premature failure of electric motor bearings caused by inverter-induced parasitic currents. We propose a novel segmented end shield design utilizing 24 carbon fiber-reinforced polymer (CFRP) lamellae to provide both structural support and galvanic isolation. The “main working” of the design relies on a segmented architecture where the lamellae are adhesively bonded between a central bearing housing and an outer mounting flange, creating a high-impedance path that interrupts circulating currents. Experimental validation focused on both mechanical stability and dielectric performance. Results indicate that the assembly maintains rotor positional integrity under nominal loads while providing an insulation resistance > 1 GΩ at 1 kV and a structural capacitance of 2.47 nF. These parameters effectively mitigate low-frequency circulating currents. Data analysis, derived from the mean values of repeated test cycles, confirms that the composite architecture serves as a viable, mechanically robust alternative to conventional metallic end shields. Full article

With the capacity of generators continuing to increase, higher demands are placed on the heat dissipation of epoxy resin (EP), the main insulation material used in stator bars and windings. To overcome its low thermal conductivity, a multiscale hybrid filler strategy was adopted to investigate the effects of spherical Al₂O₃ (10 and 1 μm), platelet BN (1 μm), and SiO₂ (50 nm) on the thermal and insulating properties of EP composites. Unlike conventional studies focusing on individual fillers, this work highlights the synergistic design of fillers with different sizes and morphologies. The filler ratios were optimized by finite element simulation, and the composites were prepared by melt blending. The results show that, at a total filler loading of 38.5 wt%, the EP composite filled with spherical Al₂O₃ particles of 10 and 1 μm, platelet BN of 1 μm, and nano-SiO₂ of 50 nm achieves a thermal conductivity of 0.5497 W/(m·K), corresponding to an increase of 158.2% compared with pure EP (0.2129 W/(m·K)). This enhancement is attributed to the synergistic effect of multiscale and multishape fillers, where large Al₂O₃ particles form the main thermally conductive framework, small Al₂O₃ particles fill the gaps, platelet BN acts as a bridging filler, and nano-SiO₂ improves the interfacial region. In addition, the composite exhibits low relative permittivity and dissipation factor tanδ in the frequency range of 10⁻²–10⁶ Hz, and its breakdown strength reaches 65.99 kV/mm. These results demonstrate that simulation-guided multiscale hybrid filler design is an effective strategy for improving the thermal conductivity of EP while maintaining acceptable insulating performance. Full article

SiO₂ aerogel cement composites (SACCs) are promising for building insulation, but how their residual thermal performance evolves after high-temperature exposure remains unclear, limiting fire protection assessment. In this study, SACC specimen with aerogel contents of 0%, 5%, 7%, and 10% were heat-treated at 400, 600, 700, 800, and 1000 °C. After cooling, their post-exposure thermal performance and microstructure were characterized via mass loss, density, thermal conductivity, MIP, and SEM. Results obtained at room temperature showed that with increasing treatment temperature, thermal conductivity first decreases and then increases, reaching a minimum after 700 °C treatment for the A7 specimens (from 0.092 to 0.063 W/(m·K)). Microstructural analysis of cooled specimens revealed that this non-monotonic behavior arises from three heat-induced changes: the cement matrix, aerogel aggregates, and the interfacial gap between them. After treatment at 700 °C, the gap corresponds to a Knudsen number of 0.01–0.02, entering the slip-flow regime. Combined with the low thermal conductivity of the cement matrix, this yields the best insulation. After treatment at 800 °C and above, the gap exceeded 60 μm, shifting heat transfer to the continuum regime and reducing insulation capacity. A thermal conductivity prediction model based on these post-exposure mechanisms agreed well with the experimental results. Full article

This study investigates the development of high-strength biofiber cement boards with enhanced thermal insulation properties by utilizing recycled biofibers derived from cement packaging bags, combined with a water-based adhesive to enhance the curing efficiency of Portland cement through a cementation–curing process. This approach reduces waste from cement packaging and other biofiber residues through recycling, thereby promoting environmental sustainability. Moreover, it does not require the use of additional chemicals for the disposal or treatment of fiber waste, nor does it require the incineration of biofiber waste. Recycled biofiber from cement bags, composed primarily of cellulose (60 wt%), lignin (15 wt%), and hemicellulose (10 wt%), serves as a reinforcing phase, while the cement and adhesive mixture functions as a strong binding matrix. The fabrication of composite materials using undamaged cement bag fibers preserves fiber integrity and enables a well-ordered one-dimensional (1D) fiber alignment, which promotes more effective reinforcement than two-dimensional (2D) or three-dimensional (3D) orientations, in accordance with the rule of mixtures. In addition, the incorporation of a water-based PVAc adhesive accelerates the curing rate of the cement phase, promoting the formation of a strong interconnected network structure, and facilitates a more complete curing process. The physical, mechanical, chemical, and thermal properties of the biofiber cement boards were evaluated in accordance with relevant industrial standards, including TISI 878:2023, BS 874, ASTM C1185, ASTM D570, ASTM C518, ISO 8301, and JIS A1412. The results indicate that an optimal cement mortar to water-based adhesive ratio of 1:2, combined with an increased number of biofiber sheet layers, significantly enhances material performance, particularly in Formulas (7)–(9). Among these, Formula (9) exhibits the lowest water absorption (0.0835 ± 0.0102%), the highest tensile strength (19.489 ± 0.670 MPa), the highest flexural strength (20.867 ± 2.505 MPa), the highest Young’s modulus (5735.068 ± 387.032 MPa), and low thermal conductivity (0.152 W/m.K). The resulting boards demonstrate strong bonding ability, enhanced resistance to fire, moisture, and weathering, and a longer service life compared to lower cement-to-adhesive ratios (1:1 and 1:0). These findings demonstrate the potential of recycled biofiber composites, combined with water-based adhesives, as sustainable alternative materials for thermal insulation and structural applications, including ceilings and walls in building construction. Full article

Mycelium-based composites (MBCs) have already been applied in various fields, like construction, architecture, packaging, waste management and many others, as sustainable replacement materials. The composites created from such materials are lightweight, biodegradable and can take many different geometrical shapes. As there are many different combinations of fungal mycelium and organic substrates, it is not only important to investigate and determine which of these combinations perform best from an acoustic perspective but also from an environmental point of view. The sound absorption qualities of these biocomposites have been investigated. It was found that the sound absorption coefficients range from 0.33 to 0.49 in the mid-high frequency range for the four different mixtures of substrate and oyster mushroom (Pleurotus ostreatus). The results from the acoustic testing are promising, but the environmental impact of these mycelium-based composites also needs to be determined. The impacts from water and especially from energy, used during the growth and preparation cycles, are the main contributors to the environmental impact of MBCs, which is also confirmed by the relevant literature. A cradle-to-grave life cycle assessment (LCA) was conducted, utilizing the ReCiPe method, with selected environmental impact categories, based on real-world production data and the scientific literature. The results obtained were also compared with a commercially produced acoustical stone wool panel. The influence on environmental impact of the different substrates is also analyzed, determining which MBC is the most environmentally friendly and has the best acoustical properties. Full article

Epoxy-glass-mica composite materials are widely used as electrical insulating materials in high-voltage rotating machinery due to their layered structure and excellent dielectric properties. Taking the F-class epoxy glass with a small amount of rubber powder mica tape commonly used as the main insulation of wind turbine stator coils as the research object, 7-day, 14-day, 21-day, and 28-day low-temperature treatment tests were conducted at −50 °C. The surface morphology and chemical structure changes of the materials were characterized by SEM and FTIR, and the influence laws of low-temperature treatment on the electrical properties of the mica tape insulation materials were systematically studied. The experimental results show that the low-temperature environment will induce microcracks and interface delamination and other structural damages, but no obvious change in the chemical structure of the mica tape was observed. With the extension of the low-temperature treatment time, the electrical properties of the mica tape show a deteriorating trend, and after 28 days of low-temperature treatment, the breakdown field strength of the F-class mica tape decreased by approximately 18.5%, and the volume conductivity overall increased by about two orders of magnitude. This indicates that the microcrack defects induced by low-temperature will lead to an enhanced electrical-thermal coupling effect in the insulation structure, thereby accelerating the degradation process of the insulation material. This reveals the degradation mechanism of wind turbine stator main insulation from “structural damage” to “performance degradation” and then to “insulation aging” under low-temperature conditions, providing a theoretical basis for the design and reliability assessment of insulation systems in wind turbine generators in cold regions. Full article

The increasing global demand for oil and gas, together with the depletion of shallow reservoirs, has driven exploration toward deep and ultra-deep formations characterized by high-temperature and high-pressure (HTHP) conditions. In such environments, conventional drill pipes often experience thermal stress, corrosion, and mechanical degradation, which can reduce drilling efficiency and compromise operational reliability. Thermal insulated drilling pipes (TIDPs) have therefore emerged as an effective solution to minimize heat transfer between drilling fluids and the surrounding formation. This review summarizes recent advances in TIDP materials, structural design strategies, fabrication technologies, and critical performance. Relevant studies were collected from major scientific databases, including Web of Science and Google Scholar, with a focus on insulation materials, coating technologies, and thermal management approaches used in drilling systems. The analysis indicates that advanced insulation systems, including polymer-based coatings, silica aerogels, vacuum-insulated layers, and phase-change materials, can significantly enhance thermal management in drilling operations. These technologies can reduce heat loss by approximately 40–60% (i.e., 400–600 W·m⁻²) and maintain drilling-fluid temperature differentials of 10–18 °C under HTHP conditions. In addition, fabrication techniques such as plasma spraying, composite fabrication, and additive manufacturing enable the development of multifunctional insulation systems with improved thermal, mechanical, and corrosion-resistant properties. Hybrid TIDP systems integrating nanocomposites and advanced polymers show strong potential for improving drilling safety and efficiency. However, challenges related to durability, scalability, and cost remain, highlighting the need for further research on multilayer insulation architectures and sustainable materials. Full article

Tree contact discharge is a key contributing factor to wildfires caused by medium-voltage insulated conductors. Prolonged abrasion of the insulation layer by branches gradually creates weak points in the insulation. When subjected to lightning strikes, these areas are prone to forming lightning-induced pinholes, which can subsequently trigger partial discharge and even ignition. This study systematically investigates the discharge-induced ignition mechanism for 10 kV overhead insulated conductors in tree contact scenarios by establishing an experimental platform integrated with high-speed imaging, ultraviolet detection, and simulation methods. Three types of typical defects were set up in the experiments: complete insulation abrasion, lightning puncture holes accompanied by localized abrasion, and lightning puncture holes without abrasion. The development process and characteristics of different discharge forms were observed and analyzed. The results indicate that the tree contact discharge ignition mechanism can be categorized into two types: thermal accumulation and direct arcing. The former occurs when insulation abrasion or composite defects exist, where sustained partial discharge or a high-resistance current leads to gradual heat accumulation, resulting in an ignition delay lasting tens of seconds. The latter occurs when only small defects such as lightning puncture holes exist in the insulation layer. A concentrated arc forms due to gap breakdown under high voltage, leading to a millisecond-level ignition process. The study found that different discharge forms produce significantly distinct ablation and carbonization patterns on both the insulation layer and the branch surface, reflecting differences in energy transfer pathways. Simulation analysis further indicated that the thickness of the insulation layer affects the electric field distribution in the tree contact gap, with the initial discharge field strength decreasing as the thickness increases. This study provides experimental evidence and classification guidance for tree contact fault monitoring, insulation condition assessment, and wildfire prevention and control in medium-voltage distribution networks. Full article

The development of high-performance composite supercapacitors remains challenging because the specific capacitance of composite electrodes is jointly governed by electronic percolation, ion accessibility, and interfacial contact, all of which are strongly affected by the balance among active materials, conductive agents, and binders. Traditional equivalent circuit modeling and empirical trial-and-error methods are often inadequate for describing these non-linear relationships and optimizing electrode design. To address this limitation, we establish a physics-guided and interpretable machine learning (ML) framework for predicting the specific capacitance of composite electrodes. Unlike traditional methods that rely on macroscopic mass fractions, our approach constructs a feature space comprising ten descriptors, including two newly introduced binder-related proxy descriptors—Binder-to-Conductive Ratio (BCR) and Specific Binder Loading (SBL)—to better represent the influence of binder content. By systematically evaluating 17 machine learning algorithms on a high-fidelity dataset, we identify the XGBoost model, optimized via Bayesian optimization, as the best predictor, achieving a coefficient of determination (R²) of 0.981 and a low mean absolute percentage error (MAPE) of 14.49%. Importantly, interpretability analysis using Shapley Additive Explanations (SHAP) provides physically interpretable statistical insights, revealing that high BCR suppresses specific capacitance through an insulating barrier effect, whereas lattice distortion in the filler material promotes ion transport. This study offers a robust, data-driven framework for optimizing composite electrode performance, demonstrating the potential of interpretable ML models for the rational design of advanced energy-storage materials. Full article

Maintenance is crucial for the durability of the existing building stock and should be perceived as an opportunity to improve the built environment. The implementation of thermal retrofitting measures to the building’s envelope enhances global energy performance, which is economically and environmentally beneficial. Building-related energy consumption during the operation phase is key to tackling carbon neutrality and climate change. Introducing thermal retrofitting within the context of maintenance planning can be cost-optimizing, as it reveals the technical–economic synergy between building pathology and energy efficiency. Maintenance activities and energy demand throughout the building’s service life influence life-cycle costs (LCCs). Decision-making based on LCC awareness is an advantage for owners. This study discusses the impact of implementing an optimal retrofitting solution (ORS), according to different maintenance strategies, on the LCC of an existing single-family home. The ORS comprises the following measures: adding an external thermal insulation composite system (ETICS) to external walls, extruded polystyrene (XPS) panels to the roof, and replacing the existing windows with others with improved thermal performance. The three maintenance strategies involve different complexity levels, concerning the type, number and timing of activities. Moving beyond isolated assessments, this study develops an integrated framework that bridges based on two existing background methodologies, involving optimal thermal retrofitting and condition-based maintenance planning, which, combined with new research, enable the assessment of maintenance, energy and global LCC for a time horizon of 100 years. The evaluation of energy-related LCC is based on simulations. The results indicate that these costs represent the majority of the global LCC. The ORS has a considerable positive impact on energy and global LCC. Adopting a maintenance strategy characterized by fewer planned activities and an earlier schedule of replacement interventions, which determines the implementation of the retrofitting measures, is better in terms of LCC savings. 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

In this study, polysiloxane-containing polyimide (si-PI) composite coatings containing hexagonal boron nitride (hBN) particles of four different sizes and at different contents were prepared, and their mechanical and tribological properties were investigated. The coatings were deposited on steel substrates via dip coating and cured at 160 °C. Their tribological properties were measured using reciprocating sliding tests under unlubricated conditions against a steel ball. The composite coatings containing nano-hBN with the smallest mean primary particle size of 0.05 μm exhibited the lowest wear. Subsequently, coatings containing 1–15 wt% nano-hBN were prepared to examine the effect of filler content. The results showed that the coatings with low nano-hBN contents (1–2 wt%) had relatively high friction coefficients and significantly reduced wear on both the coating and the counterpart. Cross-sectional scanning electron microscopy (SEM) observations revealed that dispersed small hBN aggregates suppress crack propagation through dispersion strengthening. Coatings with low nano-hBN contents (1–2 wt%) also exhibited sufficient electrical insulation. However, as the hBN content increased further, hBN agglomeration was promoted, weakening the crack-propagation suppression effect and increasing wear. These findings indicate that low-content nano-hBN/si-PI composite coatings are promising electrical erosion-resistant coatings for the outer rings of the bearings used in electric vehicle motors. Full article

To investigate the multi-factor aging mechanisms of silicone rubber used in the outer sheath of composite bushings, this study focused on HTV silicone rubber employed in the sheath layer of 1100 kV high-voltage bushings. The samples were subjected to temperature–humidity–corona coupled aging in a multi-factor aging platform. The aged samples were characterized by scanning electron microscopy, energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, hydrophobicity measurements, hardness tests, and dielectric constant measurements. The results indicate that different aging factors affect the material differently. Corona aging primarily affects the sample surface, leading to substantial methyl group detachment, surface oxidation, and a decrease in hydrophobicity, with the local static contact angle decreasing by up to 70%. In contrast, wet heat aging affects the bulk material; under high-temperature and high-humidity conditions, the internal small-molecule chains accelerate silicon-oxide crosslinking, leading to a marked increase in hardness and a relative dielectric constant that initially decreases and then increases. Considering the complex field environment, surface performance measurements are easily influenced by external factors. Therefore, hardness and relative dielectric constant are proposed as key indicators for evaluating the aging degree of silicone rubber sheaths in service. The findings provide a valuable reference for the service-life evaluation of composite bushings. Full article