Search Results (150)

Aluminum-clad steel wires are widely used in ultra-high-voltage (UHV) transmission lines due to their excellent beneficial properties. To address the inadequate strength–ductility balance of aluminum-clad steel wires for UHV applications, this study investigates the effects of cold drawing and low-temperature annealing (200~330 °C) on the microstructure, aluminum/steel interface, and mechanical properties of 20SA (20.3% IACS) aluminum-clad steel wires. The results indicate that the cold-drawn steel core exhibits high strength due to its high dislocation density and strong <110> fiber texture. Low-temperature annealing promotes overall recovery and partial recrystallization of the microstructure. Specifically, annealing at 240~280 °C significantly enhances ductility while maintaining high strength, achieving optimal strength–ductility synergy; however, higher annealing temperatures result in an unacceptably low ultimate strength, rendering them impractical for application. Interfacial characterization reveals that the as-clad and cold-drawn processes, as well as annealing below 250 °C for 10 min, maintain stable metallurgical bonding at the aluminum/steel interface, whereas annealing at 300 °C for 10 min induces the formation of brittle Fe-Al intermetallic compounds, thereby compromising service reliability. Furthermore, the precipitation of cementite (Fe₃C) with increasing temperature partially compensates for the strength loss caused by overall recovery. This study identifies the optimal heat treatment window, providing a theoretical basis for the strength–ductility design and reliable service of UHV transmission lines. Full article

To address the reliance on empirical knowledge and the lack of a quantitative basis for worker positioning in high-altitude UHV live-line work, a refined power plant model consisting of workers, transmission towers, insulator strings, and conductors has been established. Based on altitude-corrected breakdown field strength and discharge attachment criteria, entry paths and positioning for the cradle and power-driven ascender methods were optimized under IVI- and VVV-type insulator strings. Results show that field concentration is more pronounced in the middle phase. For the cradle method, a 30° approach angle is optimal, reducing body surface field strength by 9.4–18.6%, with discharge points at the toes; a sitting posture with slightly raised legs and toes pointing toward the conductor is recommended. For the power-driven ascender method, vertical entry from the side outperforms entry from below, reducing the far-tower side-phase field strength by 22–24%, with discharge points at the head; an upright, sideways posture with the face turned away from the conductor is recommended. This study provides a quantitative basis for high-altitude UHV live-line work. Full article

The long-term reliability of XLPE submarine cable insulation is influenced by progressive thermal degradation during operation and subsequent seawater ingress caused by external damage. Although thermal aging and seawater exposure have been widely investigated individually, the influence of the prior thermal-aging state on the subsequent seawater-induced degradation behavior of XLPE remains insufficiently understood. In this study, XLPE insulation specimens prepared from the same commercial compound used for 500 kV submarine cables were subjected to sequential accelerated aging consisting of controlled thermal pre-aging followed by simulated seawater exposure. Broadband dielectric spectroscopy, AC breakdown testing with two-parameter Weibull analysis, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) were employed to investigate the evolution of electrical properties, surface morphology, and molecular structure. The results demonstrate that seawater-induced electrical deterioration strongly depends on the initial thermal-aging state of XLPE. Increasing thermal pre-aging duration resulted in progressively higher relative permittivity and dielectric loss, together with reduced characteristic breakdown strength after subsequent seawater exposure. Under the most severe condition of 1440 h thermal pre-aging followed by 672 h seawater exposure, the power–frequency relative permittivity increased by 32.1%, while the characteristic breakdown strength decreased by more than one-third compared with the initial state. SEM observations revealed that thermally pre-aged specimens developed accelerated surface damage during seawater exposure, including pores, cracks, corrosion pits, and honeycomb-like structures. FTIR analysis further indicated molecular-chain degradation and increased hydroxyl-related species during sequential aging. These results suggest that thermal-aging-induced molecular oxidation, polar-group formation, and microstructural defects enhance water and ion penetration pathways, thereby increasing the susceptibility of XLPE insulation to subsequent seawater-induced degradation. This study provides material-level experimental evidence for understanding sequential aging processes in submarine cable insulation and highlights the importance of considering historical thermal damage in future condition assessment and lifetime evaluation models. Since accelerated laboratory conditions were adopted, the results should be interpreted as comparative degradation characteristics rather than direct predictions of field-service lifetime. Full article

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. Full article

Unidirectional glass fiber reinforced polymer (GFRP) composite insulators are widely used in extra-high voltage (EHV) and ultra-high voltage (UHV) transmission lines due to their outstanding electrical and mechanical performance. However, the accurate prediction of the critical buckling load is crucial to satisfy the high reliability requirement under complex operations. In this paper, an improved Perry–Robertson theory to predict the critical buckling loads of GFRP composite insulators with different slenderness is proposed. Firstly, initial imperfection is expressed as a function of the insulator strut length, which enables the critical load to be formulated as a function of slenderness explicitly. It also allows for convenient comparisons with other theories, such as Euler and Johnson’s, and easy calibration with the magnitude of initial imperfections. Secondly, the nonlinear material behavior of the GFRP composite insulator strut, resulting from changes in glass fiber orientation in relation to the loading direction during buckling, is considered to further enhance the prediction accuracy. The predicted results with current theory were validated through compression tests of GFRP composite insulators with solid and hollow struts and different slenderness and boundary conditions, which shows an accuracy of over 85%. Thus, the proposed improved Perry–Robertson theory can be also applied in other fiber-reinforced composite buckling analyses. Full article

This paper presents a miniaturized ultra-wideband high-pass filter integrated with a notch function based on low-temperature co-fired ceramic (LTCC). The design motivation is to realize continuous wideband high-pass transmission while rejecting a narrow in-band interference/leakage component in compact RF front-end modules. The proposed design employs a cascaded structure of a seventh-order quasi-elliptic HPF and a three-section $\lambda /4$ stub notch filter in a single multilayer LTCC chip. Multiple transmission zeros (TZs) are introduced to improve the lower-stopband selectivity, while the three-section coupled-line NF produces a tunable localized rejection band. The LTCC implementation further integrates multilayer capacitors, three-dimensional helical inductors, shielded strip-line coupling stubs, a grounding compensation capacitor, and an isolation wall to balance compactness, impedance matching, and parasitic suppression. The fabricated chip achieves an ultra-wide bandwidth of 2.35 octaves, a notch 20 dB FBW of 8.5%, an insertion loss below 2 dB, a 60 dB roll-off rate of 154.1 dB/GHz within the lower stopband, and a voltage standing wave ratio (VSWR) less than 2. Experimental results validate that the proposed compact chip meets communication requirements and is suitable for 5G base stations, radar systems, and other applications. The chip dimensions are 4.5 mm × 3.2 mm × 2.5 mm. Full article

Facing the demand of long-distance, high-voltage and high-power transmission, the research on MMC-UHVDC (Modular Multilevel Converter based Ultra High Voltage Direct Current) has become a hot issue. This paper focuses on the ±800 kV/8 GW UHVDC transmission system to conduct simulation modelling and insulation coordination studies. First, broadband models of the main circuit and primary equipment are established to simulate and analyse the distribution characteristics of both switching and lightning transient overvoltages under typical faults. Second, based on the overvoltage severity at critical nodes, two surge arrester configuration schemes with distinct internal valve protection topologies are proposed. Finally, an Improved Fuzzy Analytic Hierarchy Process (FAHP) is introduced to perform a quantitative techno-economic evaluation of the comparative schemes. The results demonstrate that the optimised configuration successfully suppresses extreme overvoltages at vulnerable sub-module nodes, maintaining adequate insulation margins. These research findings provide a highly reliable mathematical framework and engineering reference for the safe design of UHVDC systems. Full article

High-altitude, low-pressure environments significantly reduce the insulation strength of air gaps, posing severe risks to live-line working on Ultra High Voltage and Extra High Voltage (UHV/EHV) transmission lines. To address this challenge and ensure operational safety, this paper proposes a predictive gap discharge voltage calculation model based on the dynamic coupling of time-varying electric fields and space charge. Unlike existing approaches that rely on static, geometry-dependent empirical corrections, the proposed model achieves high predictive capability by intrinsically mapping air relative density and absolute humidity to dynamically modify key microscopic discharge parameters, including the effective ionization coefficient, attachment coefficient, and streamer internal electric field strength. This physical framework enables the successful simulation of the complete progression from streamer inception to leader development and final breakdown, thereby calculating the 50% breakdown voltage under varying altitudes and gap distances. To rigorously validate the proposed model, breakdown tests were conducted using simplified sphere–plane gaps and full-scale simulated gaps between a human worker and a tower window at altitudes of 23 m and 2100 m. Additionally, third-party experimental datasets were utilized for comprehensive comparative analysis. The results demonstrate that the model’s predictive values align excellently with multi-source experimental data, establishing its high accuracy and practical engineering value for complex electrode configurations under diverse high-altitude conditions. Full article

To address the issues of thermal non-uniformity and insulation aging of converter transformers operating under long-term high electric field and high-temperature conditions in ultra-high-voltage direct current (UHVDC) transmission systems, this paper investigates the temperature field distribution characteristics of converter transformers based on electro–thermal–mechanical multiphysics coupling. By establishing a full-scale multiphysics simulation model of a ±800 kV converter transformer, the interactions among the electric field, temperature field, and mechanical stress field are comprehensively considered. The temperature gradient distribution and hotspot formation mechanisms within the valve-side winding and the lead-out structure are revealed. The results show that the internal temperature distribution of the converter transformer is non-uniform, resulting in a nonlinear distribution of material parameters in oil-paper insulation, which significantly affects the insulation performance. The research findings provide a theoretical basis and engineering reference for the structural optimization and thermal stability improvement of the main insulation system of converter transformers. Full article

Ultra-high-voltage direct-current (UHVDC) transmission systems impose stringent requirements on the reliability of insulation materials used in converter transformer bushings. Epoxy resin systems are key insulating materials in resin-impregnated paper (RIP) capacitor bushings, and their processing characteristics, curing behavior, and electrical properties directly affect bushing performance. In this study, two epoxy insulation systems used for resin-impregnated paper (RIP) bushings, namely the imported Araldite LY1564/Aradur 3486 system and the domestic EP-2020/CA-3015 system, were systematically investigated through viscosity, curing, and electrical property tests. The results show that the viscosities of both resins decreased significantly with increasing temperature. At 60 °C, the viscosities of Resin A and Resin B were 151.6 mPa·s and 156.3 mPa·s, respectively. The mixed resin–hardener systems exhibited similar viscosity evolution and comparable pot life characteristics. DSC measurements revealed two-stage curing reactions for both materials, with first exothermic peak temperatures of 65.4 °C and 96.3 °C and second peak temperatures of 269.3 °C and 269.8 °C for Materials A and B, respectively. Electrical testing demonstrated that both materials exhibited similar temperature-dependent dielectric and resistivity behavior, with dielectric loss increasing at elevated temperatures and resistivity decreasing as temperature increased. The volume resistivity trends and dielectric characteristics of the two materials remained highly consistent throughout the investigated temperature range. The results indicate that Material B exhibits processing performance, curing characteristics, and electrical insulation properties comparable to those of Material A. Therefore, Material B demonstrates strong potential for application in UHVDC RIP bushing insulation systems and provides a promising alternative for the localization of key insulating materials. Full article

Against the backdrop of global carbon neutrality, the cross-regional allocation of green electricity is pivotal for energy transition, yet its impact on inclusive economic growth and regional equity remains contentious. This study addresses the spatial welfare mismatch arising from large-scale power transmission in China. Utilizing provincial panel data from 2006 to 2022 and employing the staggered rollout of Ultra-High Voltage (UHV) lines as a quasi-natural experiment, we apply advanced econometric models, including CS-DID and Bartik instrumental variables, to identify causal effects. Empirical results reveal an asymmetric “cost-benefit separation” effect: while green electricity imports significantly bolster high-quality development (HQD) in eastern recipient regions, exports exert a drag on western provinces by triggering capital outflow, profit deprivation, and ecological load. Consequently, regional HQD gaps exhibit divergence rather than convergence. However, we find that fiscal ecological compensation acts as a critical moderating buffer, effectively reversing this trend and driving conditional convergence and sustainable regional development. Heterogeneity analysis further indicates that market-oriented electricity reforms and “East Data, West Computing” infrastructure mitigate these negative externalities. These findings underscore the necessity of shifting from a purely engineering-focused transmission model to an institutional framework centered on energy justice, offering actionable insights for achieving SDG 7 and SDG 10 synergies. Full article

With the ongoing trend of miniaturization and intelligent power transmission equipment, the compact design of environmentally friendly gas-insulated switchgear (GIS) has emerged as a critical technical challenge. This study presents a detailed case study of a 40.5 kV dry air-insulated switchgear under specific dimensional constraints. Specifically, the cabinet width was reduced from 1000 mm to 800 mm, significantly narrowing the phase-to-phase and phase-to-ground clearances. A high-fidelity three-dimensional electric field model was established using the finite element method to evaluate the dielectric stress distribution within the enclosure. Numerical results indicate pronounced electric field concentrations at critical regions—including copper busbar joints, disconnector contacts, and the inlet bushing shielding rings—where local intensities exceeded the insulation safety threshold. To mitigate these issues, integrated design refinement strategies were evaluated, encompassing the structural modification of shielding rings, the application of silicone rubber coatings, and insulation reinforcement via heat-shrinkable tubing. Comparative analysis and experimental results demonstrate that the refined configuration effectively suppressed the peak electric field intensity. Finally, the design was validated through comprehensive dielectric tests, including a 215 kV lightning impulse withstand voltage test. This work may offer useful engineering references and quantitative data for the ultra-compact design of eco-friendly switchgear under similar constraints. Full article

Ultra-high-voltage (UHV) converter transformer equipment is critical for UHVDC transmission systems. This paper proposes a Cross-modal Transformer framework for fault diagnosis by fusing dissolved gas analysis (DGA) and infrared (IR) thermography data. The framework encodes DGA measurements into temporal tokens and processes IR images through a ResNet-18 backbone to generate spatial tokens. A Cross-modal Transformer module enables deep semantic interaction via bidirectional cross-attention, allowing DGA tokens to attend to relevant IR regions and vice versa. A modality-gating mechanism adaptively reweights the two modalities under measurement degradation, including partial and fully missing-modality scenarios. The novelty lies in adapting these components into a leakage-controlled DGA-IR diagnostic framework for UHV converter transformers, with explicit interaction between gas-evolution tokens and spatial thermal tokens. Evaluation is performed under a leakage-controlled grouped chronological split that isolates equipment units, converter stations, and fault episodes across train, validation, and test partitions. Labels are drawn exclusively from maintenance inspection and operational records, independent of the IEC 60599 ratio features seen by the model. Under this protocol, the proposed framework consistently improves accuracy and macro-F1 over encoder-matched simple-fusion baselines (Transformer-DGA + ResNet-18 with concatenation, late fusion, and gated averaging). Additional missing-modality, noise, and ablation experiments indicate that the gains come from bidirectional cross-attention and adaptive gating rather than from stronger unimodal encoders alone. Full article

This study examines how power transmission infrastructure expansion reshapes manufacturing agglomeration and regional industrial systems. Taking China’s ultra-high-voltage (UHV) transmission projects as a quasi-natural experiment, we investigate their impact on manufacturing agglomeration. Using panel data from 282 prefecture-level cities over the period 2006–2020, we adopt a comprehensive empirical strategy centered on a multi-period difference-in-differences (DID) framework, complemented by synthetic DID, propensity score matching, instrumental variable approaches, and double machine learning methods to ensure robust causal inference. The results show that UHV projects significantly promote manufacturing agglomeration, indicating a substantial reconfiguration of regional industrial systems. This effect operates through increased power supply in input areas, the release of resource advantages in output areas, and market scale expansion. Both input and output sides have significant positive effects, with a stronger impact from the input side. Moreover, government intervention and infrastructure development further amplify the agglomeration effect. Furthermore, the manufacturing agglomeration induced by UHV projects promotes economic growth, green development, and urban sustainability. These findings provide system-level insights into the role of power transmission infrastructure in energy–industrial integration and offer implications for the design and optimization of sustainable energy systems. Full article

The electrical connection structure of the grid-side bushing of a converter transformer is a core current-carrying component in ultra-high voltage direct current (UHVDC) transmission systems. Under seismic conditions, it is prone to overheating and discharge faults, endangering the safe operation of converter stations. To reveal the damage mechanism and temperature evolution law of the electrical connection structure under seismic conditions, this paper establishes a refined finite element model for the structure and conducts seismic response analysis. Combined with the empirical formula of contact resistance and the electrothermal coupling model, the evolution of contact resistance and distribution characteristics of the temperature field of the electrical connection structure under different seismic peak accelerations are analyzed. The results indicate that earthquakes disrupt the stress distribution at the electrical contact interface, causing eccentric load and stress concentration, reducing the effective high-stress current-carrying area. The contact resistance rises rapidly with increasing acceleration, leading to severe degradation of current-carrying performance. The increase in contact resistance results in a manifold increase of Joule heat, and both the maximum and minimum temperatures of the structure increase significantly as acceleration rises. This study clarifies the mechanical–electrothermal coupling response mechanism of the structure, providing theoretical basis and technical support for its seismic design, thermal stability evaluation, operation, maintenance, and overhaul. Full article