To investigate the effect of grafting modification on the carrier migration characteristics of polypropylene (PP) elastomer composite insulation, a composite insulation of antioxidant grafted modified PP blend thermoplastic elastomer is prepared. The evolution laws of direct current (dc) conductivity and dc integral charge [DCIC- Q(t) ] of the composite insulation are studied, and the influence mechanism of grafting modification on the distribution characteristics of charge traps is analyzed. Research has found that compared to unmodified composite insulation, graft-modified composite insulation can reduce leakage current by 33.4% under high temperature and high electric field, increase the threshold field for charge injection by 30%-50%, significantly reduce the accumulation of space charge, and increase the trap energy level, exhibiting stronger trapping of carriers. Through experiments and simulations, it was found that grafting not only introduced localized deep trap states in the energy levels of PP, increasing the trap density, but also enhanced the intermolecular interaction energy, thereby restricting carrier migration under high temperatures and high electric fields, ultimately improving the insulating performance of the material.

The operational status monitoring of transformers is critical for the stability of the power grid. However, conventional monitoring methods are limited by low sensitivity and reliance on external power sources. Internal faults in transformers are often accompanied by characteristic variations in leakage magnetic fields, making leakage-field monitoring a direct approach for condition assessment. Here, a hybrid electromagnetic-triboelectric nanogenerator (EM-TENG) based on bacterial cellulose (BC)/graphene oxide (GO)/cobalt ferrite (CoFe2O4) composite film (BGC) is developed. BC is selected as the insulating matrix due to its compatibility with oilimmersed transformer environments. GO constructs a conductive network to enhance charge transport, while CoFe2O4 nanoparticles introduce magnetic responsiveness. Under an external magnetic field, the output voltage of the EM-TENG increases by 43.69%, indicating the excellent magnetic responsiveness of the composite structure. Furthermore, the device achieves a magnetic field sensitivity of 50 mV & sdot;mT-1, enabling efficient conversion of leakage magnetic field variations into electrical signals. As a proof of concept, it successfully drives a digital timer and enables a self-powered leakage magnetic field fault monitoring and alarm system. This work offers a viable self-powered strategy for high-sensitivity transformer condition monitoring toward smart grid applications.

Epoxy resin insulation is widely used in high-voltage power equipment, where they endure complex electromechanical stresses. This study examines the effects of dynamic electromechanical stress on electrical tree growth in epoxy resin under simultaneous AC voltage and cyclic stress. The results show that under high cyclic stress, tensile stress promotes residual stress release, thereby enhancing tensile strength and suppressing electrical tree propagation. In contrast, compressive stress induces fatigue damage, leading to strength reduction and accelerated tree growth. Under low cyclic stress, fatigue striations contribute to improved mechanical strength; however, tensile stress facilitates defect extension and tree initiation, whereas compressive stress inhibits treeing via defect closure. Reverse trees arise under compressive stress due to high resistivity in forward channels. Tensile stress produces wider, slower-growing trees with higher partial discharge amplitude, fewer counts, and narrower phase ranges, while compressive stress leads to narrower, faster-growing trees with lower amplitude, more counts, and broader ranges. These behaviors result from stress-induced dielectric variations that reshape local field distribution and partial discharge activity, ultimately governing tree evolution. This study provides new insights into electromechanical stress-driven insulation degradation and informs epoxy insulation design for long-term reliability in high-voltage equipment.

Epoxy resin in dry cable terminations suffers serious dielectric failure under low-temperature conditions, due to embrittlement-induced fracture toughness degradation and partial discharges. This work engineers epoxy-based composites by incorporating poly(methyl methacrylate)-block-poly(butyl acrylate)-block-poly(methyl methacrylate) (PMMA–b-PBA–b-PMMA) triblock copolymers that achieves 42% fracture toughness enhancement at -40°C, while preserving glass transition temperature (Tg > 117 °C) and stable dielectric performance. When the doping content is 20 wt%, the elongation at break increases from 2.54% to 5.49% at -40 °C, corresponding to a 116% increase. Dielectric loss measurements show that the modified samples maintain low loss values across the temperature range from -80 to 40 °C, confirming their suitability for low-temperature insulation applications. Under 14 kV AC voltage, optimized formulations exhibit 51% enhancement of partial discharge inception voltage and 260% extension of electrical tree breakdown time. These improvements are attributed to the formation of nanoscale domains, wherein PBA-rich regions absorb fracture energy via nanocavitation, and PMMA-rich regions restrict chain mobility and homogenize electric fields. This distinctive molecular architecture endows the epoxy composite with simultaneously enhanced low-temperature toughness and electrical insulation performance, demonstrating promising application potential in epoxy-based power equipment.

As the second part of this work, effects of gamma-ray irradiation (0-250 kGy) on the AC breakdown strength of isotactic polypropylene (iPP) are investigated. The radiation resistance of samples with various crystallization properties is evaluated based on the degradation in breakdown strength. The trap distribution is characterized to analyze charge transport behavior. The degradation mechanism is explored through microstructural characterization using high-temperature gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The results demonstrate that the trap level of each sample remains stable below 80 kGy but decreases dramatically at 250 kGy. As the irradiation dose increases, distinct trends emerge that the breakdown strength of α-iPP decreases more significantly than that of β-iPP. At 250 kGy, β-iPP exhibits 31.4% higher breakdown strength than α-iPP. β-iPP demonstrates superior radiation resistance, maintaining higher molecular weight after high-dose irradiation.

Residual stress generated during curing is a critical factor related to the explosive electrical breakdown of GIL/GIS epoxy Insulators. To further investigate the influence of residual stress on the breakdown process, this study establishes a residual stress model of the basin-type insulator as well as a phase-field breakdown simulation model incorporating electro–mechanical coupling effects. The results indicate that during the curing process, sedimentation of Al2O3 particles leads to a non-uniform density distribution within the basin-type insulator, which in turn results in an uneven distribution of residual stress. The residual stress is mainly concentrated at the interface between the basin-type insulator and the metal insert, and this concentration is more pronounced in low-density regions. Moreover, an excessively high cooling rate further intensifies stress concentration in basin-type insulator. Further breakdown simulation results demonstrate that the first principal stress induced by residual stress during curing promotes the breakdown development of the basin-type insulator. However, as the temperature gradient ΔT increases, the first principal stress is gradually released, thereby suppressing the breakdown process to a certain extent. In addition, the proposed simulation model can accurately reproduce a recent practical failure case, verifying the reliability of the model.

Zinc oxide (ZnO) varistor blocks, commonly integrated into cable sheath protectors, generate substantial active power loss under harmonic voltage stress to accelerate the thermal aging. To investigate the aging behavior of ZnO varistors of protectors subjected to high-order harmonic voltages, this study implements a high-temperature accelerated aging test to simulate long-term thermal stress, while the key electrical degradation indicators are obtained through the leakage current measurements. The extrapolated aging time derived from the experiments is modeled by using a three-parameter Weibull distribution. In combination with a likelihood ratio testing method, the life distribution characteristics and reliability variations of ZnO varistors under different harmonic conditions are quantitatively analyzed. The results show that the life evaluation based on the three-parameter Weibull distribution reveals a 34% reduction in average service life under the 51st harmonic voltage compared with that under the 3rd harmonic voltage for aged ZnO varistors. These findings provide critical insights for the reliability design and maintenance decision-making of ZnO varistors under harmonic stress scenarios, ultimately contributing to the enhancement of the safety and longevity of power systems.

Gas-insulated switchgears (GISs) and gas-insulated transmission lines (GILs) are essential for large-capacity power transmission in demanding environments, such as high drops, large spans, and heavy pollution. As the core components providing both electrical insulation and mechanical support, ultra-high voltage (UHV) epoxy-based insulators often suffer from high internal residual stress. This issue, compounded by a lack of reliable detection methods, frequently results in equipment being commissioned with hidden defects. To address this, this review first examines the formation mechanisms of curing deformation and residual stress in oversized insulators based on cure kinetics and thermo-chemical coupling models. Subsequently, it provides a comprehensive summary of current residual stress measurement techniques, comparing the applicability and limitations of embedded sensors, direct mechanical measurements, and indirect non-destructive testing (NDT) methods. Finally, by coupling residual stress with filler sedimentation, the stress distribution patterns and mechanical reliability of epoxy-based insulators across different life-cycle stages are analyzed. These insights offer valuable theoretical references for the structural design, process optimization, and performance evaluation of oversized epoxy-based insulators, ultimately contributing to the intrinsic safety of UHV power equipment.

Designing effective interfaces for aramid fiber/epoxy (AF/EP) composites in electrical insulation applications is particularly challenging, given that interfacial failure is prone to occur at the AF/EP interface due to charge accumulation and inherent modulus mismatch. Inspired by mussel byssus and nacre, a bionic interface modification strategy is developed in this study, which integrates polydopamine coating and nanosilica (SiO2) onto the fiber surface through a hierarchical assembly approach. The results show that the interfacial shear strength and interlaminar shear strength of the composites are improved by 126.46% and 47.86% respectively, due to the synergistic effects of enhanced interface bonding strength, mechanical interlocking and successful construction of gradient modulus transition layer. Furthermore, more charge traps and energy scattering centers are introduced by SiO2. Consequently, interfacial insulation degradation process under high voltage is significantly suppressed in the channel length, cumulative damage area, and breakdown time. Compared to the unmodified AF/EP composites, the modified composites demonstrate exceptional dielectric properties with DC conductivity decreased by 83.38%, dielectric loss reduced by 10.36% and breakdown strength enhanced by 29.43%. This interface functionalization strategy provides novel insights into the performance improvement of AF/EP composites for high-end power equipment subjected to combined electrical and mechanical stresses.

This paper investigates the evolution of space charge (SC) and electric field (EF) in factory joints (FJs) for ±500 kV submarine cables under DC and polarity reversal (PR) conditions. The FJ insulation samples are prepared for PEA and SPD measurement. A charge transport model for FJ insulation is established and validated. The results show that, compared with the cable insulation (CI), the reinforcing insulation (RI) with a shorter degassing time overall exhibits a higher impurity content, higher carrier mobility, and shallower trap levels. These differences result in the interfacial charge accumulation. Under DC voltage, the interfacial charge density increases with polarization time, weakening the interfacial EF and increasing its angular deviation. As the temperature gradient (ΔT) increases, the combined effects of SC and interfacial charge lead to a gradual rise in the EF on the outer side of the insulation transition region. During PR, charge recombination is the dominant behavior at the interface. The SC and interfacial charge are not fully dissipated at the end of PR, making the interface a critical location for EF distortion. The maximum interfacial EF at ΔT = 30 °C increases by 76.63% compared with that at 0°C, confirming that a higher ΔT exacerbates EF distortion. This study reveals the SC and EF characteristics in FJ insulation under different conditions, which have potential significance for the design and reliability enhancement of HVDC submarine cable systems.

This work focuses on improving the breakdown strength of low-density polyethylene (LDPE) by doping nano-SiO2 grafted with aromatic compounds terminated by alkyl chains. In the first part of the work, quantum chemical calculation is employed to estimate and select the aromatic compound. The selected aromatic compound is grafted onto the nano-SiO2 surface via an amidation reaction. Alkyl chain is grafted as the terminal group of the aromatic compound to enhance the compatibility between the additive and the LDPE matrix. Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and zeta potential measurements are systematically utilized to verify the surface treatment effectiveness of nano-SiO2. The compatibility between the modified nanoparticle and the LDPE is estimated through molecular dynamics simulation. The results confirm the successful surface grafting of nano-SiO2 with 4, 40' -stilbenedicarboxylic acid (SDA) terminated by alkyl chains. The alkyl chain improves the compatibility of the SDA-grafted nano-SiO2 with the LDPE matrix by strengthening the intermolecular interactions. This approach is expected to enhance the breakdown strength of LDPE.

The impact of temperature gradient on the surface charge accumulation on the insulator of direct current gas-insulated switchgear (dc-GIS) under long-time charging is a crucial issue for insulation reliability in the power system. In this study, an improved model based on the bipolar charge transport (BCT) and gaseous ion flow calculation is proposed to simulate the surface charge accumulation on a real-size insulator used in 320-kV dc-GIS with the temperature gradients of 0 degrees C, 15 degrees C, 30 degrees C, and 45 degrees C for 2000 h. The results show that, as the temperature gradient grows from 0 degrees C to 45 degrees C, the maximum density of positive charge on the insulator convex surface increases by 75.1% at 2000 h. The region of accumulated positive charge extends with the charging time on the concave surface, while it shrinks on the convex surface. The dominant accumulating process converts from the electrode injection to the gas phase ionization during surface charging. It is suggested that the surface charge accumulation is intensified under the condition of higher temperature gradient with long-time dc charging, which is determined by the competition of electrode injection and gas phase ionization.

The widespread application of aramid fiber/epoxy composites in high-voltage equipment is severely hindered by weak fiber-matrix interfacial interactions, which can trigger mechanical and dielectric failures. To tackle this bottleneck, this paper constructs a robust multiscale interface by anchoring nanosilica onto plasma-pretreated aramid fibers via a bio-inspired polydopamine (PDA) adhesive layer. This synergistic modification fundamentally transforms the interface. Mechanically, the multiscale structure promotes strong physical interlocking and chemical bonding, increasing the interfacial shear strength. Electrically, the introduction of nano-silica creates charge traps that severely restrict carrier migration. Consequently, the composites exhibit superior insulation stability, achieving a 5.02fold increase in DC resistivity and a 32.47% enhancement in AC breakdown strength at an optimal nano-silica loading. This interface modification strategy provides a promising pathway for fabricating highly reliable dielectrics for power systems.

Polypropylene (PP)-based materials have attracted considerable interest as sustainable candidates for high-voltage cable insulation. Composed of crystal and amorphous phases, its macroscale dielectric properties are closely related to this mesoscale heterophase structure. However, due to the lack of testing methods capable of quantitatively characterizing the dielectric property differences between crystal and amorphous phases, theories on the insulation degradation of semicrystalline polymers lack effective data support. This study establishes an experimental approach leveraging the asymmetric thermal behavior of impact polypropylene copolymers, complemented by numerical simulations, to deconstruct and quantify the intrinsic dielectric parameters of both phases. Results showed that the amorphous phase, owing to its lower deep-trap density, exhibits markedly weaker suppression of charge migration than the crystal phase. This disparity leads to a one-order-of-magnitude increase in conductivity and induces severe electric field distortion (46%) at the crystal-amorphous interface, which is identified as the primary driver of insulation degradation. Building on these insights, we propose a synergistic modulation strategy targeting both crystal morphology and the crystal phase itself through the incorporation of alpha/beta composite nucleating agents. This method substantially mitigates both the magnitude and the spatial extent of electric field distortion, thereby enhancing insulation stability. Overall, this work not only provides data and theoretical basis for understanding insulation degradation in semicrystalline polymers but also offers guidance for developing high-performance dielectrics.

Under combined mechanical and electrical stresses, aramid fiber reinforced epoxy composites (AFRPs) suffer insulation failures due to interface damage and partial discharges. In this study, epoxy network topology is modulated by hyperbranched epoxy resin (HER) to improve electrical insulation performance of AFRPs. The result shows that the incorporation of 5% and 10% HER could simultaneously improve breakdown strength and toughness of the resin samples, while maintaining good mechanical modulus. This is attributed to the enhanced crosslinking degrees and heterogeneous free volume distribution as evidenced by molecular simulation results. In-situ breakdown tests under combined mechanical and electrical stresses demonstrate that the modified AFRPs display markedly lower decline ratios in breakdown strength compared to the unmodified AFRPs, especially under high tensile stress. Damage analysis indicates that the optimized topological structure with moderate HER content (less than 10%) improves crack resistance of aramid fiber/epoxy resin interface, thus uniforming local electric field distribution and improving breakdown strength. The design of the epoxy crosslinked network enables the AFRPs with superior mechanical and insulation performance, providing theoretical foundations for their application in electrical insulation systems.

Polypropylene (PP) is the mainstream dielectric material for high-energy-density capacitors. However, its dielectric performance deteriorates markedly at elevated temperatures. Blending cyclic olefin copolymer (COC) with PP can improve the high-temperature dielectric stability of the material. Nevertheless, the limited compatibility between PP and COC tends to induce defects, thereby constraining the breakdown strength. In this study, a styrene-ethylene/propylenestyrene (SEPS) triblock copolymer was incorporated into polypropylene/cyclic olefin copolymer (PP/COC) blends at different loadings as a compatibilizer. SEPS was found to optimize the morphology of the dispersed phase and enhance interfacial adhesion, thereby effectively suppressing interfacial polarization and charge accumulation. This mechanism not only significantly reduces dielectric loss and alleviates electric-field distortion, but also enhances the breakdown strength and hightemperature stability of the material. Compared with the control groups, the introduction of an appropriate amount of SEPS markedly improved the dielectric performance, resulting in an 15.1% increase in the breakdown strength of the film at elevated temperature and a 38% increase in energy density. These results provide a feasible strategy for the development of hightemperature-stable dielectric materials for energy storage.

Epoxy resin is widely used in high-voltage insulation. However, it is highly susceptible to electrical treeing, which is a critical factor limiting its reliability. In this work, the growth of electrical trees was investigated under complex electric fields and mechanical stress gradients. Finite element simulation and Digital Image Correlation (DIC) validated the gradient establishment. A needle-wire electrode system was employed to evaluate the influence of mechanical stress gradients on electrical tree development, and a phase-field model analyzed the degradation mechanism. Results indicate that increased stress gradients significantly accelerate electrical tree development. Mechanism analysis reveals that stress gradients directly induce driving energy gradients, creating localized energy concentration points that intensify molecular chain fracture. Furthermore, reverse stress gradients yielded a longer time to breakdown relative to the forward gradient condition, attributed to the modulating effect exerted as the tree propagates toward the driving energy minimum zone. These findings highlight the regulatory role of internal stress gradients on electrical tree behavior, offering theoretical insights for optimizing epoxy insulation structures.

DC-GIL insulators are key components that provide both electrical insulation and mechanical support. However, their insulation and mechanical designs have traditionally been developed separately, without accounting for the influence of mechanical stress on insulation breakdown. This study investigates how mechanical stress affects the breakdown strength of epoxy/Al2O3 composite samples at various temperatures. Results show that breakdown strength decreases significantly with increasing mechanical stress, and this effect becomes even more pronounced at elevated temperatures. The security region of DC-GIL insulators can be defined as the region bounded by the breakdown-strength ( E-B ) and tensile-strength ( sigma(B) ) intercepts on the coordinate axes. Accordingly, the criterion E/E-B+sigma /sigma(B) < 1 can be used to assess the safety margin of DC-GIL insulators.

Epoxy resin insulation is widely used on offshore power platforms and is subject to complex electromechanical stresses. This study investigates the impact of cyclic tensile stress on the electrical tree growth of epoxy resin composites under both preloaded and on-loading conditions. The results indicate that cyclic tensile stress not only induces the fatigue damage but also promotes the release of residual stress. When the stress amplitude is low, the fatigue damage dominates, accelerating the electrical tree growth as the stress frequency increases. In contrast, at higher stress amplitudes, the release of residual stress becomes more dominant, slowing down the electrical tree growth with the increasing frequency. Preloaded cyclic stress does not directly affect the electrical tree growth but enhances the residual stress release with the increasing stress amplitude, thus slowing down the electrical tree growth. Conversely, on-loading cyclic stress directly accelerates electrical tree growth, and as the stress amplitude increases, the growth rate of electrical trees also increases. Both the fatigue damage and the residual stress release effects are associated with the relaxation of physical and chemical crosslinks in epoxy resin. The strain energy density is used to quantitatively characterize the contribution of cyclic stress to electrical tree growth, with results aligning closely with the experimental trends.

The essence of pulse separation is decoupling multi-source pulses. The performance of pulse separation directly constrains the accuracy and engineering application value of partial discharge (PD) detection and diagnosis. Recent algorithms suffer from insufficient robustness when dealing with pulse clusters in overlapping separation regions. Moreover, when deployed at the edge, the algorithm struggles to balance operational efficiency and computational resource consumption. To address these issues, we improve and optimize a dual-mode density peak clustering algorithm for edge deployment. First, the algorithm can automatically select between the Manhattan distance mode and the cross-correlation distance mode according to the overlapping degree of pulse clusters, thereby achieving optimal separation. Meanwhile, an edge deployment optimization scheme is designed to address the efficient embedding of the algorithm in PD detection devices. Experimental results indicate that the cross-correlation distance mode excels at separating overlapping clusters, while the Manhattan distance mode suits non-overlapping ones. In complex three-source scenarios, the optimized algorithm achieves an accuracy of 98.7% with an overall separation duration of 11.837 s. Its precision and computational efficiency are significantly higher than those of classical methods. The algorithm provides an effective solution for detecting complex insulation defects.