Search Results (200)

AC power cables play an important role in power systems, in the transmission and distribution of electrical energy. For this reason, to ensure high operational reliability, voltage withstand tests and diagnostic tests are performed at every stage of their technical life to determine the condition of cable insulation. Due to the large electrical capacitances of cable systems, modern testing methods use very low frequency (VLF) and damped oscillating (DAC) voltages. The research presented in the article analyzed the effect of the test voltage waveform parameters on the partial discharge (PD) inception conditions in spherical gaseous voids present in the XLPE insulation of AC cable model. Using COMSOL 6.1 and MATLAB R2021b, a coupled electro-thermal model of a 110 kV AC cable was implemented, for which the critical gaseous void dimensions were estimated and phase-resolved PD patterns were generated for the rated voltage and the VLF and DAC test voltages specified in the relevant standards. In the analyses for the rated voltage, the influence of internal temperature distribution, which causes modification of XLPE permittivity, was taken into account in the numerical cable model. Full article

In order to ensure the continuous and reliable supply of electrical energy to the power grid, it is necessary to evaluate and monitor the degree of impairment of the insulation of electrical cables, as throughout its service life, insulation around cables suffers degradation due to numerous stress factors, which can arise from both environmental and operational causes. This aspect has aroused deep interest among energy professionals, as well as the industrial sector, with focus mainly placed on the undesirable effect caused by unexpected and sudden process stoppages, as well as their consequent financial and social impacts. That said, this article presents a methodology for evaluating the degree of insulation aging using the partial discharge progression curve. For this purpose, a thermal oven was duly constructed, in accordance with the technical premises presented in the literature, capable of homogeneously heating conductor samples. After thermal cycles, these conductors were aptly handled and tested in a controlled laboratory environment to determine the partial discharge progression curve. Through accurate data processing, a correlation was obtained between the degradation of the insulation and the rate of increase in partial discharge. The results are promising, as they provide support for maintenance agents’ ability to monitor and intervene regarding conductors. Full article

Ensuring the fire resistance and thermal stability of power cables is crucial for their reliable performance in fire environments, essential for sustainable power distribution, and allowing for more time to extinguish fires and for evacuation. This study utilises numerical simulation to analyse the thermal behaviour of fire-resistant medium-voltage cable, focusing on the impact of conductor radius and material properties under external heat flux. A heat transfer model of cables with conductor radii of 3 mm, 5 mm, and 7 mm under a localised external heat flux of 750 °C was developed. The results show that smaller conductors stabilise faster (reaching the steady state at 45 min for 3 mm vs. 79 min for 7 mm) but experience higher thermal stress, with conductor temperatures peaking at 692.5 °C. Larger conductors enhance axial heat conduction, reduce steady-state temperature by up to 25%, and improve heat dissipation by over 360%. The 5 mm conductor radius provided balanced performance, lowering the temperature by 65 °C compared to 3 mm, although it remained 20.1% hotter than the 7 mm. The ceramic layer played a crucial role in reducing heat flux in the heat source section. Optimised polyethylene insulation and ceramic material improved heat retention and surface temperature control in non-heat source sections. Also, thermal resistance analysis decreased from 1.00 K/W (3 mm) to 0.65 K/W (7 mm). Among material properties, increasing ceramic thermal conductivity had a more significant impact on reducing core temperature than improving insulation. These findings provide practical recommendations for optimising conductor geometry and material properties for more fire-resistant cables. Full article

Reducing the environmental impact is a key reason for developing recyclable insulation materials for high-voltage industries. In this study, polypropylene (PP) blends were prepared via melt mixing with styrene–ethylene–butylene–styrene (SEBS), a thermoplastic elastomer, to improve breakdown strengths at various cooling speeds. A systematic investigation was conducted to evaluate the influence of crystal size, degree of crystallinity, and nucleation growth rate on the breakdown strength. Crystallization behavior was analyzed using isothermal and non-isothermal methods based on the Avrami model. Increasing SEBS content reduced crystallinity, with the lowest nucleation growth rate observed at 35% SEBS. Breakdown strength correlated with crystallization behavior and was further validated by Weibull distribution method. Notably, PP/SEBS blends containing 35% SEBS exhibited the highest breakdown strength of 66.4 kV/mm at a cooling speed of 10 °C/mm. This improvement reflected a reduction in the degree of crystallinity from 36.0% to 22.9% and the lowest growth rate constant (k) at 35% SEBS. Furthermore, the predicted lifetime of PP/SEBS blend containing 35% SEBS, calculated using the oxidation induction time and the Arrhenius equation, was 42 years. These findings demonstrate that SEBS content and cooling rate effectively modulate crystallization and breakdown strength, enabling recyclable PP/SEBS with XLPE-comparable performance for sustainable high-voltage insulation. Full article

A cable accessory is a critical component in constructing high-voltage direct current (HVDC) power grids, and it is typically composed of multiple materials. Due to the discontinuity of the insulation medium, it is prone to failure. This study focuses on a two-layered composite insulation medium simplified from HVDC cable accessories, and its surface potential decay (SPD) characteristics are related to the space charge transport characteristics. Previous studies on surface charge migration have been limited and primarily focused on single-layered insulation materials. However, the actual insulation structure is mostly composite. Therefore, it is of great practical significance to explore the surface charge migration characteristics of two-layered structures. This study presents a bipolar charge transport model after pre-depositing surface charges to investigate the surface charge migration characteristics of an ethylene–propylene–diene monomer (EPDM)/polyethylene (PE) two-layered polymer film. The effects of charge injection and trap related to nano-doping, local defects, and thermal aging on the surface potential decay (SPD) and space charge distribution in EPDM/PE were analyzed. The results show that the increase in the electron injection barrier slows surface charge dissipation and inhibits charge accumulation at the interface. An increase in the trapping coefficient leads to a higher surface potential in the stable state and a greater space charge density. During the early depolarization stage, the SPD rate is weakly dependent on the trap depth, with charge migration primarily governed by the external electric field. Full article

Aiming at the challenge of trajectory planning for a continuum manipulator in the confined spaces of gas-insulated switchgear (GIS) chambers during intelligent operation and maintenance of power equipment, this paper proposes a configuration space (C-space) obstacle-avoidance planning method based on an improved RRT-Connect algorithm. By constructing a virtual joint-space obstacle map, the collision-avoidance problem in Cartesian space is transformed into a joint-space path search problem, significantly reducing the computational burden of frequent inverse kinematics solutions inherent in traditional methods. Compared to the RRT-Connect algorithm, improvements in node expansion strategies and greedy optimization mechanisms effectively minimize redundant nodes and enhance path generation efficiency: the number of iterations is reduced by 68% and convergence speed is improved by 35%. Combined with polynomial-driven trajectory planning, the method successfully resolves and smoothens driving cable length variations, achieving efficient and stable control for both the end-effector and arm configuration of a dual-segment continuum manipulator. Simulation and experimental results demonstrate that the proposed algorithm rapidly generates collision-free arm configuration trajectories with high trajectory coincidence in typical GIS chamber scenarios, verifying its comprehensive advantages in real-time performance, safety, and motion smoothness. This work provides theoretical support for the application of continuum manipulator in precision operation and maintenance of power equipment. Full article

The present study explores and verifies the chemical modifications achieved by grafting 4-formylcyclohexyl heptanoate (FH) and 4-(2,5-dioxopyrrolidin-1-yl) cyclohexane-1-carbaldehyde (CC) onto addition-curing silicone rubber (SiR). These modifications aim to enhance the electrical insulation performance, moisture resistance, and pyrolysis tolerance of the SiR material, thereby improving its suitability for reinforced insulation in power transmission systems. First-principles calculations demonstrate that both the chemical graft modifications can introduce shallow hole traps of 0.3~0.4 eV and deep electron traps of 0.9~1.0 eV into the polymer molecule of addition-curing SiR for inhibiting charge transport and injection. It is indicated from first-principles oxidation reaction pathways that the chemical grafting of FH or CC contributes positively, rather than impacts negatively, to the oxidative stability of addition-curing SiR. We also reveal how the two proposed species of organic molecules as grafting agents can act on modifying water adsorption uptake, heat capacity, molecular thermal vibration, and polymer pyrolysis of the SiR material, which are highly accountable for its resistances to high-temperature electrical breakdown, moisture aging, and thermal spikes of partial discharge. The comprehensive molecular simulations and material calculations demonstrate that both the grafted agents can significantly intensify polymer molecule aggregations, restrain molecular thermal vibrations, and reduce water adsorption uptakes. One of the preferable graft agents (CC) can also considerably improve polymer pyrolysis tolerance, while contributing to improved high-temperature electrical breakdown strength and moisture resistance of addition-curing SiR. This research highlights the significant potential of graft modification in molecular compositions to improve the electrical insulation, moisture resistance, ambient-temperature thermal stability, and pyrolysis tolerance of addition-curing SiR, offering valuable insights to develop competent elastomeric polymer applied for cable accessory insulation. Full article

Moisture ingress in power distribution cable bodies can lead to insulation degradation, jeopardizing the operational safety of power grids. However, current cable maintenance technologies lack effective diagnostic methods for identifying moisture defects in cable bodies. To address this gap, this paper proposes a dynamic frequency domain reflectometry (D-FDR) method for moisture localization and diagnosis in power distribution cables. Leveraging the temperature-sensitive nature of moisture defects—in contrast to the temperature-insensitive characteristics of other defects—the method involves the application of thermal excitation to induce differential dynamic changes in the distributed capacitance of moisture-affected cable segments compared to normal segments, enabling the precise identification and diagnosis of moisture ingress. Simulations and experiments confirm that moisture ingress in cable bodies increases the distributed capacitance, generating reflection peaks at corresponding distances on frequency domain localization plots. Under thermal excitation, the reflection peak amplitude of moisture defects exhibits a temperature-dependent decrease, distinct from the behavior of intact cables (amplitude increase) and copper shielding layer damage (negligible variation). By utilizing the dynamic characteristics of reflection peak amplitudes as diagnostic criteria, this method is able to accurately localize and diagnose moisture defects in cable bodies. Full article

The continuous distribution ability of electricity is defined as the effectiveness of the computation of reliability indices. Therefore, we conducted a reliability assessment and evaluated the performance of the distribution system in the Freeport Area of Bataan (FAB). For reliability assessment, software was developed to automate the computation of indices, including system average interruption frequency index (SAIFI), system average interruption duration index (SAIDI), customer average interruption frequency index (CAIFI), and customer average interruption duration index (CAIDI). Through reliability assessment and evaluation, the low-performing distribution network of the FAB was successfully identified. After the identification of the low-performing network, reconductoring and redundant feeder line projects were proposed to alleviate and reduce the occurrence of power interruptions. An analysis of its economy was also conducted, and the result showed that line reconductoring from bare conductor to insulated cable was the most feasible option since it resulted in a high benefit–cost ratio (BCR) and a positive net present value (NPV) for all evaluated cases. Full article

Currently, zero-emission targets require future global energy concepts to be based on renewable energy sources; therefore, huge investments are being made in bulky offshore wind parks worldwide. In this context, there is ongoing and enormous development and a need for HVDC submarine cables (both static and dynamic) to connect offshore wind farms. One of the basic problems when analyzing the operating conditions of HVDC cables is assessing the effects of the load current, which generates thermal and electric fields on the insulation systems in these cables. This article considers the problem of the influence of the thermal effect and space charges—the field effect—on the electrical conductivity of polymeric insulating materials and, thus, on the distribution of the electric field intensity in the cable insulation. An analytical methodology for joint analysis of the thermal-effect- and space-charge-related influence is presented. The critical value of the electric field intensity at which the electrical conductivity is significantly modified under coupled thermal–electric exposure is determined. Special focus is placed on the analysis of the coefficient representing the dependence of the electrical conductivity on the temperature in a much broader range than typically assumed. Hence, the intention of this paper is to highlight the limit values of the electric field strength under the simultaneous action of the space charge and temperature gradient. Recognizing the changes in the electric field intensity value in the insulation is of fundamental importance from the point of view of HVDC cable technology and construction. Full article

HVDC cable systems are becoming an upscaled technical option, compared to AC, because of various factors, including easier interconnections, lower losses, and longer transmission distances. In addition, renewables providing direct DC energy, electrified transportation, and aerospace where DC can be favored because of higher carried specific power all point in the direction of broad future usage of HV and MV DC links. However, contrary to AC, there is little return from on-field installation as regards long-term cable reliability and aging processes. This gap must be covered by intensive research, and contributing to this research is the purpose of this paper. The focus is on key points for HVDC (and MVDC) cable reliability and sustainability, from design modeling able to account for voltage transients and extrinsic aging (such as that caused by partial discharges) to the impact of aging on insulation conductivity (which rules the electric field distribution, thus aging rate). Also, recyclable and nanostructured materials, as well as health conditions, are considered. It is shown how cable design can account for accelerated aging due to voltage transients, as well as for aging-time dependence of conductivity, and how design can be free of extrinsic aging caused by PDs. Algorithms for health condition evaluations, which have additional value in a relatively new technology such as HVDC polymeric cables, are applied to insulation system aging under partial discharges, showing how they can provide an indication of insulation degradation globally or locally (weak spots) and of possible maintenance times. All of this can effectively contribute to reducing the risk of major cable breakdown and damage under operation, which would significantly affect the return on investment (ROI). Full article

To investigate the impact of temperature variations during the secondary crosslinking of cross-linked polyethylene (XLPE) on the insulation performance of the interface layer, commercial XLPE cable pellets were subjected to flat hot pressing at 140 °C, 160 °C, 180 °C, and 200 °C. XLPE insulation interface layers were prepared at different secondary crosslinking temperatures. The samples were characterized by gel content, differential scanning calorimetry (DSC), thermal elongation test, power frequency breakdown voltage, and scanning electron microscope (SEM). Key parameters, including crosslinking degree, crystallinity, thermal elongation, and characteristic breakdown voltage of the samples, were obtained. The results indicate that as the secondary crosslinking temperature increases, the crosslinking degree of the samples rises, while thermal elongation initially decreases and then increases. Crystallinity shows a decreasing trend overall. The characteristic breakdown voltage shows a trend of increasing first and then decreasing. When the temperature is 180 °C, the characteristic breakdown voltage reaches its maximum value. Therefore, increasing the secondary crosslinking temperature can help improve the mechanical and electrical properties of the XLPE insulation interface layer. However, crystallinity decreases at excessively high temperatures, which has a negative impact on insulation performance. Full article

High-voltage underground cables inevitably experience frequency-dependent electromagnetic (EM) losses, driven primarily by skin and proximity effects. These losses become more severe at higher harmonic frequencies, which are increasingly common in modern power networks. In traditional multi-segment cable designs, uninsulated conductor bundles enable large circular eddy current loops that elevate AC resistance and exacerbate both skin and proximity phenomena. This paper investigates the impact of introducing a thin insulating layer between individual conductor strings in a five-segment high-voltage cable model. Two insulation thicknesses, 75 µm and 100 µm, are examined via two-dimensional finite element (FE) harmonic analysis at 0, 50, 150, and 250 Hz. By confining eddy currents to smaller loops within each conductor, the insulating layer achieves up to a 60% reduction in AC losses compared to the baseline uninsulated model, lowering the ratio of AC to DC resistance from about 3.66 down to 1.47–1.49 at 250 Hz. The findings confirm that adding even a modest inter-strand insulation is highly effective at mitigating skin and proximity effects, with only marginal additional benefit from thicker insulation. Such designs offer improved energy efficiency and reduced thermal stress in underground cables, making them attractive for modern power distribution systems where harmonic content is pervasive. Full article

The intermediate joint of high-voltage cables, as a critical component in the power transmission system, plays a direct role in the stable operation of the entire electrical system. In recent years, frequent explosions of intermediate joints in high-voltage cables have led to significant economic losses and safety risks. Therefore, studying the explosion mechanisms and explosion prevention measures of high-voltage cable intermediate joints is particularly important. This article provides a systematic review of the explosion mechanisms and explosion prevention measures for high-voltage cable intermediate joints. It begins by introducing the composition of cable systems and the structural features of the 220 kV prefabricated cable joint. Next, the article elaborates on the spatiotemporal evolution process of cable joint explosions. Typically, a cable joint explosion undergoes several stages: partial discharge, arc breakdown, and insulation material decomposition, which ultimately leads to explosion and ignition. Subsequently, the article reviews each of these dynamic stages in detail. Finally, the article discusses the existing explosion prevention measures and their shortcomings, and proposes future directions for the development of explosion prevention measures. This article can provide a theoretical foundation and technical reference for the research on the explosion mechanisms of high-voltage cable joints, as well as for the development of explosion prevention measures. Full article

As critical infrastructure in modern distribution systems, power cables face progressive insulation degradation from partial discharge (PD), while conventional recognition methods struggle with feature extraction and model generalizability. This study develops an integrated experimental platform for PD pattern recognition in power cable systems, comprising a control console, high-voltage transformer, high-frequency current transformer, and ultra-high-frequency (UHF) signal acquisition equipment. Four distinct types of discharge-defective models are constructed and tested through this dedicated high-voltage platform, generating a dataset of phase-resolved partial discharge (PRPD) spectra. Based on this experimental foundation, an improved Swin Transformer-based framework with adaptive learning rate optimization is developed to address the limitations of conventional methods. The proposed architecture demonstrates superior performance, achieving 94.68% classification accuracy with 20 training epochs while reaching 97.52% at the final 200th epoch. Comparisons with the original tiny version of the Swin Transformer model show that the proposed Swin Transformer with an adaptive learning rate attains a maximum improvement of 6.89% over the baseline model in recognition accuracy for different types of PD defect detection. Comparisons with other deeper Convolutional Neural Networks illustrate that the proposed lightweight Swin Transformer can achieve comparable accuracy with significantly lower computational demands, making it more promising for application in real-time PD defect diagnostics. Full article