This article presents an ultrasonic intelligent diagnostic method for internal defects in ultrahigh voltage basin insulators using an improved YOLOv8 model. This approach addresses the limitations of manual interpretation in traditional ultrasonic inspections by enabling automatic analysis and intelligent defect identification. The proposed method incorporates a deeper network architecture with optimized loss functions and adaptive feature extraction mechanisms, significantly enhancing adaptability in complex scenarios. Compared to YOLOv5 and YOLOv8n, the improved model achieves a 7% and 3% increase in ${F}1$ score, respectively, along with a 13.6% and 10.3% improvement in mAP@0.5. Experimental validation on standard defect samples and a three-phase common box basin insulator demonstrates the model's capability to detect 1 mm-scale bubbles and cracks with less than 2% localization error, over 80% diagnostic confidence, and 93.5% consistency with industrial Digital Radiography (DR) inspections, providing a robust and intelligent solution for defect detection in critical power system components.

When high-voltage DC equipment is subjected to polarity-reversing voltage, the insulation performance of its internal insulation material, epoxy resin-impregnated paper (RIP), is significantly affected by low-frequency polarization. To clarify the underlying mechanisms, this study analyzes the impact of the relationship between low-frequency dielectric relaxation time and polarity-reversing time on the dynamic changes of space charges at different temperatures based on the pulsed electro-acoustic (PEA) method. Furthermore, the influence of traps at the epoxy resin (EP)/RIP interface on interfacial charge accumulation is considered. By improving the existing bipolar carrier transport model, the dynamic characteristics of interfacial space charges in RIP under different polarity-reversing times are explored. The results show that at 313K, due to the low-frequency dielectric relaxation time constant exceeding 60s, the charge distribution is not significantly affected by the reversal time; At 333K and 353K, the reduction in dielectric relaxation time leads to a decrease in interfacial charge density and maximum field strength, with the peak field strength shifting towards the epoxy layer; At 373K, influenced by space charge dissipation and enhanced relaxation effect, the electrode surface charges and the maximum field strength in the epoxy layer initially decrease and then increase with increasing reversal time. The simulation results more explicitly characterize the interfacial polarization process between EP and RIP, and together with the experimental results, elucidate the mechanism of low-frequency polarization on the dynamic characteristics of space charges in RIP under polarity-reversing voltage. The research results may provide a theoretical basis and reference for the insulation design and optimization of high-voltage DC equipment.

The valve-side bushing of converter transformer is a critical component in both AC and DC power grids and plays an essential role in ensuring the safe and stable operation of power systems. Flashover at the gas–solid interface between the valve-side bushing core and SF₆ is closely related to surface charge accumulation. Understanding surface charge accumulation characteristics under DC voltage is therefore of great significance for the reliable operation of valve-side bushings. In this study, the isothermal surface potential decay method was employed to investigate the trap distribution of epoxy resin impregnated paper used in valve-side bushing cores at different temperatures. The trap distribution of epoxy resin impregnated paper samples coated with TiO2 was also measured. The DC creepage flashover performance of coated and uncoated samples in SF₆ was further examined. The experimental results indicate that, with increasing temperature, the shallow trap density increased while the deep trap density gradually decreased for both types of samples. Moreover, the TiO2 coating reduced the deep trap energy level of epoxy impregnated paper at temperatures above 70 °C. In cylindrical sample tests, the TiO2 coating altered the surface conductivity of epoxy-impregnated paper, thereby modifying the charge distribution at the gas–solid interface. In DC surface flashover tests conducted in SF6, the average flashover voltage of TiO2-coated samples was 66.47 kV, which was higher than that of epoxy resin impregnated paper sample’s 55.70 kV. This coating effectively enhanced the creepage flashover voltage and exhibited superior resistance to electrical tracking. These findings provide guidance for the design of surface coatings for valve-side bushing cores aimed at promoting charge dissipation and improving resistance to electrical tracking.

ABSTRACT As a commonly used bushing current‐carrying structure in recent years, contactor‐type electrical connection parts operate in a complex environment of electric, thermal and chemical corrosion for extended periods. With the increase of ultra‐high voltage (UHV) transmission capacity, its operating environment faces more stringent challenges, and the stability of their operation is directly linked to the reliability of the UHV transformer equipment. This paper aims to investigate the mechanism behind contact failure by developing a contactor deterioration test platform in oil to study the deterioration and corrosion process of strap contactor in oil under 120°C environment. The study found that the sulphur element content on the exposed copper surface of the strap contactor was elevated from 0% to 2.05% in 28 days, and there was an obvious latency period for the sulphide corrosive reaction with the surface of the strap contactor. The electrical contact resistance of the strap contactor after the corrosion reaction was elevated from 110 to 251 μΩ, which became overheating failure and contact failure of electrical connection components of bushings.

With the rapid development of high-voltage DC (HVDC) power systems, accurate measurement of surface electrostatic potential on insulating components has become critical for electric field assessment and insulation reliability. This paper proposes an electrostatic potential sensor based on cantilever micro-vibration modulation, which employs piezoelectric actuators to drive high-frequency micro-vibration of cantilever-type shielding electrodes, converting the static electrostatic potential into an alternating induced charge signal. An electrostatic induction model is established to describe the sensing principle, and the influence of structural and operating parameters on sensitivity is analyzed. Multi-physics coupled simulations are conducted to optimize the cantilever geometry and modulation frequency, aiming to enhance modulation efficiency while maintaining a compact sensor structure. To validate the effectiveness of the proposed sensor, an electrostatic potential measurement platform for insulating components is constructed, obtaining response curves of the sensor at different potentials and establishing a compensation model for the working distance correction coefficient. The experimental results demonstrate that the sensor achieves a maximum measurement error of 0.92% and a linearity of 0.47% within the 1-10 kV range. Surface potential distribution measurements of a post insulator under DC voltage agreed well with simulation results, demonstrating the effectiveness and applicability of the proposed sensor for HVDC insulation monitoring.

This study investigates the thermal aging behavior of bamboo paper and wood paper and their epoxy resin impregnated composites. The results reveal that although both materials follow a common “degradation-reorganization” aging path, their mechanisms differ fundamentally due to inherent structures. Bamboo paper exhibits higher chemical reactivity arising from its greater hemicellulose and lignin content, leading to more extensive oxidative degradation, as evidenced by a 66% increase in carbonyl index versus 53% for wood paper, a faster decline in thermal decomposition temperature, and a higher char residue rate. Crystallinity analysis shows a non-monotonic evolution in both papers, with wood paper maintaining a consistently higher crystallinity index throughout aging. Dielectric measurements demonstrate that the epoxy resin impregnated bamboo paper composites develop a more reactive interface, producing broader interfacial polarization, higher relaxation strength and conductivity, and a more dynamic three-stage dielectric evolution, with parameters 30% to 50% higher than those of the epoxy resin impregnated wood paper composites. Havriliak-Negami model analysis reveals that the epoxy resin impregnated bamboo paper composites possess higher charge mobility and a wider trap energy distribution. Separate analysis of the shape parameters further identifies fundamentally different interfacial polarization evolution modes, with the bamboo composites exhibiting α1-dominated broadening of the relaxation time distribution and stable β1, whereas the wood composites display a β1-dominated decline. These findings demonstrate that wood paper undergoes structure-modulated aging with relatively stable progression, while bamboo paper follows chemically driven aging characterized by more complex degradation and interfacial restructuring.

This paper presents a trapezoidal toothed log-periodic ultra-high frequency antenna for partial discharge (PD) detection in high-voltage power equipment. The proposed antenna features a novel trapezoidal toothed structure and a systematic parametric optimization process, achieving an impedance bandwidth of 0.5–3 GHz (VSWR < 5) and a maximum gain of 6.34 dBi at 1.75 GHz. Experimental validation in a controlled sulfur hexafluoride (SF6) gas environment demonstrates the antenna’s ability to detect weak PD signals with a high signal-to-noise ratio of up to 20 dB and generate clear phase-resolved partial discharge (PRPD) patterns. The obtained PRPD patterns aligning well with theoretical expectations and commercial detection systems, highlighting the antenna’s potential for real-time PD monitoring and fault diagnosis in high-voltage power systems.

Epoxy-Al2O3 composites is the main material of HVDC GIL insulator, whose space charge characteristics are closely related to the safety of device. In production, semiconducting electrodes are respectively coated on the surface of the high voltage rod and grounding inserts to increase the bonding strength between the metal and the insulator. This paper studies the effect of semiconducting electrode on the space charge behavior of EA composites. In this paper, the EA composites for GIL insulator are firstly prepared. The epoxy-based semiconducting electrode (ER) and chloroprene rubber-based semiconducting electrode (CR) are coated on one side of the EA-1 and EA-2 samples, and then sputtering silver electrode (Ag). And Ag is the cathode and anode of EA-0. The space charge characteristics in each samples are measured by pulsed electroacoustic method under different polarity electric fields at 25 °C, 40 °C 60 °C and 80 °C. The results show that the number of electrons and holes injected from the ER and CR is similar, and the distribution of space charge seems to be less affected by the semiconducting electrode at low temperature. But the effect of ER and CR on charge distribution is obviously different at high temperature, and ER has better performance than CR in controlling charge injection.

Dielectric polymer capacitors are essential for electrostatic energy storage but suffer from charge transport‐induced energy losses, particularly at elevated temperatures where thermally activated charge carriers exacerbate conduction. Conventional mitigation strategies rely on introducing heterogeneous interfaces to create charge traps, complicating scalable film fabrication. A homogeneous molecular trapping mechanism would circumvent these complexities, yet remains underexplored. Herein, a charge trapping strategy is devised by modifying the lowest occupied molecular orbitals of dielectric polymers through Lewis acid‐base adduct formation. The use of tris(pentafluorophenyl)boron (BCF) as a Lewis acidic molecular additive introduces deeper charge traps in commercial polyetherimide (PEI) while retaining homogeneity. With only 0.5 wt.% loading, the PEI‐BCF film exhibits greatly improved breakdown strength, achieving an ultrahigh discharged energy density of 7.3 J cm −3 with excellent cycle stability at 200 °C. This work establishes a facile molecular approach to decoupling charge trapping from heterogeneous interfaces, enabling high‐energy‐density polymer capacitors operable under extreme thermal conditions.

The digital twin technology plays a crucial role in enabling the intelligent operation and maintenance of power equipment, as well as facilitating the digital transformation of the power industry. High voltage (HV) converter transformer valve side bushing is a critical equipment in high voltage direct current (HVDC) transmission projects and the coupling effect of its multi-physical fields determine the operation state of the equipment. Therefore, there is an immediate necessity to develop key digital twin technology for HV bushings, allowing for real-time monitoring of multiple physical field to support their reliable operation. The paper adopts the finite element method to construct a model for electro-thermal coupling field of the converter transformer valve side bushing. By solving electro-thermal coupling finite element equations, snapshots are obtained and electro-thermal coupling field of the bushing is efficiently computed using singular value decomposition and proper orthogonal decomposition (POD). The results demonstrate that electro-thermal coupling field distribution obtained through the reduced-order model closely matches that computed by commercial software, significantly reducing the required computation time. This research validates the effectiveness of utilizing POD for fast computation and real-time simulation of electro-thermal coupling field of HV converter transformer valve side bushings.

Fractional frequency transmission (FFT) technique has emerged as a prospective solution for achieving carbon neutrality and enabling long-distance transmission of offshore wind power. During the long-term operation of FFT lines, main cable insulations inevitably face challenges of charge accumulation and electrical aging under complex conditions involving electric fields, temperature variations, and frequency drops. Herein, we have developed a modified space charge measuring system, with rapid detection capabilities, to evaluate space charge characteristics of low-density polyethylene (LDPE) used in FFT lines. Pulse electroacoustic (PEA) testing results indicate that charge accumulation intensifies at low-voltage frequencies, while elevated temperatures significantly increase carrier mobility, leading to hetero charge accumulation and deteriorated electric field distortion. Comprehensive theoretical analysis through bipolar charge transport (BCT) modeling and numerical simulations further support experimental findings, revealing that as the frequency increases, energy release concentrates at sample edges and causes material degradation. This study offers a rational pathway for understanding charge behaviors and is beneficial for the optimal design of cable insulation in FFT systems (FFTSs).

ABSTRACT In order to achieve the online analysis of the status of the current carrying structure by using the limited number of external sensors in three‐phase integrated gas insulated transmission line (GIL), this paper proposes a data‐driven fast calculation method for the temperature distribution with deep‐learning reduced‐order model, to address the efficiency issue of finite element and other numerical methods in real‐time applications. This method combines a proper orthogonal decomposition (POD) with the BP neural network (BPNN) and the deep convolutional neural network (DCNN) based on U‐net structure, respectively, so that the accuracy and efficiency of temperature calculation in the solid and fluid domains can be well balanced. A lower‐dimensional approximate system of the temperature in solid domains is constructed by POD so that the computational scale can be reduced. BPNN is introduced to map the external sensors data of the GIL to the feature coefficient obtained by POD nonlinearly. The DCNN based on U‐net structure is developed to estimate the temperature of the fluid domains by learning the feature of the solid domains, so as to obtain the overall temperature distribution. The results show that the proposed framework can rapidly and accurately predict the thermal state of sliding contact section in three‐phase integrated GIL with limited external data, where the maximum relative error is less than 1.0%. The proposed method achieves an acceleration factor of 5.6 × 10 3 compared with the numerical simulation software, providing an available option for the real‐time visualization and digital twin diagnosis of GIL temperature distribution.

This paper proposes a transfer learning-based surrogate-assisted multi-objective optimization method for the valve-side electrostatic ring insulation structure of converter transformers, considering electro-thermal coupling effects. Low-cost pure electrostatic simulations are used as source domain data, while a limited number of high-fidelity electro-thermal simulations serve as target domain data. A deep neural network-based transfer learning surrogate model is constructed to reduce training time while ensuring high prediction accuracy and generalization. Key design variables are identified through Sobol global sensitivity analysis, and the sample space is generated via Latin hypercube sampling. Two surrogate models are trained to predict the minimum oil-gap insulation margin under AC conditions and the maximum electric field strength in the pressboard under DC conditions. These models are integrated into the NSGA-II multi-objective optimization framework, and TOPSIS is used to select the best compromise solution from the Pareto front. Results show that the proposed method improves the minimum oil-gap insulation margin by 8.87% and reduces the maximum electric field strength in the pressboard by 11.90%. Compared to conventional methods relying solely on electro-thermal simulations, the proposed approach achieves comparable accuracy while reducing model construction time by approximately 67.76%.

Under long-term exposure to high dc voltage, the converter transformer valve-side bushing will accumulate surface charge at the solid insulation interface, which affects the distribution of electric field inside the bushing and even triggers the bushing insulation failure. To address the problem of surface charge accumulation in converter transformer bushing, this article builds a bushing core surface potential measurement system, proposes a bushing dc field model considering weak gas ionization and surface conductivity, and carries out experimental measurements and simulation analyses on the surface potential distribution characteristics of the bushing core. Meanwhile, the transient change process of the bushing electric field under dc withstand voltage is simulated and calculated for the actual ultrahigh-voltage (UHV) converter transformer valve-side bushing structure. The results show that the surface potential distribution of the bushing core has a nonlinear relationship with the applied voltage, and there is a polarity effect, while the surface current is the dominant factor for the surface charge accumulation. The research results of this article can provide a theoretical basis for the insulation structure design of converter transformer valve-side bushing and play an important supporting role in improving the reliability of bushing insulation.

As a key current-carrying structure of high-voltage bushings, the reliability of electrical connection components is crucial to the safe and stable operation of power equipment. To obtain the microstructural evolution of electrical connection components with different deterioration states, CUD strap contactors were deteriorated in different ways, and electron backscatter diffraction technique was used to test the microstructure of strap contactors with different deterioration states. The results showed that compared to the unused contactors, the contact resistance of the contactors under the combined effect of friction and high temperature increased 203.12 times and was in a failed state. During the process from unused state to wear deterioration, high temperature deterioration, and then to eventual failure of the contactors, the average grain size gradually grows from 8.15 mu m to 25 mu m, the dislocation density gradually decreases from 2.38 x 10(14) m(-2) to 1.04 x 10(14) m(-2), and there are a significant proportion of the recrystallized organization. These changes are detrimental to the mechanical properties of the contactors. In addition, the distribution of grain boundaries in the contact area proves the occurrence of over-temperature phenomenon in this area, which will accelerate the deterioration of the contactors and eventually lead to the failure of the component. The relevant conclusions can provide a theoretical basis for the design of electrical connection structure of strap contacts as well as the study of deterioration mechanism.

Bamboo grows rapidly and can be continuously recycled, which is beneficial for environmental protection. What is more, bamboo exhibits good pulping performance second only to softwood and can to some extent replace the softwood pulp. However, currently, the insulating paper used in the electrical industry is mostly made of softwood pulp. In this article, the properties of transformer insulating oil-bamboo paper, which is used in oil-filled electrical equipment, were researched. The thermal aging characteristics of bamboo paper and softwood paper impregnated with insulating oil were compared. Based on the research results, it is found that the degree of polymerization (DP) of bamboo paper is obviously higher than that of softwood paper in the middle and late aging period despite the DP of new bamboo paper is lower than that of new softwood paper. The dissolved gas content and the acid value in the oil of the insulating oil-bamboo paper system are significantly lower than that of the insulating oil-softwood paper system throughout the aging process, which indicates the lower reactivity of the bamboo paper with transformer oil. The conductivity of the insulating oil-bamboo paper is relatively lower, and the breakdown strength is higher than that of the insulating oil-softwood paper in the middle and later stages of aging, which proves that the insulating oil-bamboo paper has better electrical performance during aging process. It is indicated that insulating oil-bamboo paper has more excellent structural stability and thermal aging resistance than traditional insulating oil-softwood paper.

ABSTRACT Resin impregnated paper (RIP) converter transformer valve‐side bushings are the key equipment in converter stations. Local overheating of the RIP core not only reduces the transmission efficiency but also causes insulation failure of converter transformers. In this paper, a new heat dissipation structure is proposed to improve the temperature distribution homogeneity of the bushing using two‐phase closed thermosyphon (TPCT). A test model is developed to determine the optimal working fluid inventory. Then, the temperature distribution of a ± 400‐kV RIP converter transformer valve‐side bushing with an optimised heat dissipation structure is obtained using the coupled three‐dimensional electromagnetic‐fluid‐thermal numerical simulation method considering multiphase flow and phase change processes. The influence of the new structure on the electric field is analysed. The simulation result is verified by the temperature rise test. The results show that two‐phase closed thermosyphon can reduce the maximum temperature of the RIP valve‐side bushings and significantly improve the temperature distribution homogeneity.

In recent years, surface flashover faults have occurred frequently in the core of the converter transformer valve side bushing, and the surface charge distribution at the gas-solid interface directly affects the insulation performance along the surface of the core. High-precision surface charge inversion algorithms are essential for studying the accumulation characteristics of charge at the gas-solid interface. This article establishes a method that uses B-spline basis functions as the basis for surface charge inversion. Through geometric mapping, normalized nearly uniform B-spline curves and cyclic B-spline curves are mapped onto the surface of the object under test. The basis functions representing the surface charge distribution of the object are constructed by the product of the B-spline curves in the height direction of the sample and those in the circumferential direction. A simulation is conducted to construct the overdetermined equations relating potential and charge, achieving efficient and stable solutions using the LSMR iterative algorithm and the GCV regularization parameter selection method. This article demonstrates the advantages of B-spline basis functions in characterizing the continuous distribution of surface charges at the gas-solid interface through fitting examples of 2-D continuous functions using both B-spline and binary rectangular window basis functions. It is verified that B-spline basis functions can achieve better inversion results with fewer basis functions in the surface charge inversion process, thus reducing computational complexity. Finally, the reliability of using B-spline basis functions as the basis for inversion is validated through dust pattern experiments and inversion of measured data.

Epoxy/paper composites are critical materials in drytype bushings for Ultra-High Voltage Direct Current (UHVDC) systems. Understanding the aging behavior of epoxy/paper composites under combined electrical and thermal stresses is crucial for ensuring the reliable operation of insulation systems. The study investigates the changes in dielectric properties and space charge distribution in epoxy/paper composites subjected to both thermal aging and electrothermal aging. The results show that both aging conditions lead to significant degradation in the electrical properties, but electrothermal aging causes more pronounced effects. Specifically, the relative permittivity initially decreases in thermal aging due to the decomposition of residual curing agents, but it increases as the material undergoes further aging. In electrothermal aging, the relative permittivity increases immediately due to the combined effects of thermal and electrical stresses, leading to structural damage and more pronounced interfacial polarization. Additionally, space charge accumulation is higher in electrothermal aging compared to thermal aging, as the electric field concentrates stress at internal interfaces, accelerating material degradation. These findings provide valuable insights into the aging mechanisms of epoxy/paper composites, highlighting the need to consider both electrical and thermal stresses in the design and operation of high-voltage equipment.

Free metal particles within HVdc gas-insulated transmission line (GIL) pose a significant threat to insulation integrity. This article presents a multiscale dynamic simulation method for micrometer-sized metal particles in HVdc GIL systems. It establishes an adhesion simulation model for these metal particles and captures their macroscopic movement in conjunction with microscopic properties. Based on this model, the collision characteristics of particles of algorithms, sizes, and shapes are analyzed. The simulation results indicate that the critical adsorption velocity of ellipsoidal particles with an eccentricity of 5 is six times greater than that of particles of the same size. The belly of the tri-post insulator is identified as a high-risk area for the adsorption of metal particles. While increasing the particle trap length enhances capture efficiency, a saturation phenomenon occurs, which varies with the electric field of the GIL insulator. Following simulation analysis, the optimal trap length is determined to be 550 mm. These studies provide methodologies for the accurate simulation of metal particles and contribute to particle pollution control and the reliability enhancement of HVdc GIL equipment.