Search Results (172)

A novel interfacial coating agent was developed by modifying silicone oil with polycyclic aromatic hydrocarbons (PAHs) to enhance the insulation performance of HVDC cable accessories. This study investigates the effects of corona and hot–cold cycle aging on the DC breakdown characteristics of the Cross-Linked Poly Ethylene and Ethylene Propylene Diene Monomer (XLPE/EPDM) interface. Interfacial breakdown tests, infrared spectroscopy, and a microstructural analysis were employed to investigate aging mechanisms. The results show that PAH-modified silicone oil significantly increases the breakdown voltage, with 2,4-dihydroxybenzophenone (C₁₃H₁₀O₃) identified as the optimal additive via quantum chemical calculations (QCCs). Even after aging, the modified interface maintains its superior performance, confirming the long-term reliability of the coating. Full article

The goal of this paper is to evaluate the life of HVDC extruded cables subjected to the extension of qualification test (EQT) load cycles, introduced by Cigrè Technical Brochure 852, as well as to compare the results thus obtained with those formerly obtained by the authors in the case of the prequalification test (PQT) load cycles. This goal has been achieved in the present investigation by properly modifying a previously developed procedure for the life and reliability estimation of HVDC cables—implemented in Matlab^TM environment—to make it applicable to EQT load cycles in addition to PQT and type test load cycles, which are already considered in the former version of the procedure. Considering a 500 kV DC-XLPE cable as the case study, the time-varying temperature profile and electric field profile within the cable insulation are calculated. Then, the fractions of life lost and the life of the cable at five locations within the insulation thickness are evaluated by means of a proper electrothermal life model. A comparison between the electric field distributions, fractions of life lost, and cable life under EQT and PQT is carried out. In this way, important features of the EQT compared to the PQT load cycles are singled out, and eventually, a new modified extension of qualification test (MEQT) is proposed as a feasible and meaningful compromise between the pros and cons of the EQT and PQT. Full article

This paper addresses the challenges of efficient electric vehicle (EV) charging integration in Direct Current (DC) microgrids (MGs), particularly the impact of intermittent EV loads on power sharing and voltage regulation. Traditional droop control methods suffer from inherent trade-offs between performance indices of parallel distributed energy resources (DERs), which in turn results in improper source utilization. We propose a novel decentralized piece-wise droop control (PDC) approach with voltage compensation for EV charging to overcome this limitation and to minimize the unequal cable resistance effect on power sharing. This strategy dynamically optimises the droop characteristics based on EV charging load profiles, partitioning the droop curve to optimize power sharing accuracy and voltage stability considering the constraints of maximum allowable voltage deviation and loading. Simulation and experimental results demonstrate significant improvements in power sharing, enhanced DER utilization, and voltage deviations consistently within 2.5% when compared with traditional strategies. PDC offers a robust solution for enabling efficient and reliable EV charging in MGs, as it is not sensitive for EV load prediction errors and measurement noise. Full article

Offshore wind power has a broad development prospect, but with the development of offshore wind farms to the deep sea, the traditional high-voltage AC transmission has been difficult to adapt to the offshore wind power transmission distance and transmission capacity needs. A flexible DC transmission system applying modular multilevel converter is a common scheme for offshore wind power, which has been put into use in actual projects, but it is still facing the problems of high cost of offshore converter station platforms and high loss of collector systems. In order to improve the economy and reliability of the medium- and long-distance offshore wind power delivery systems, this paper proposes a diode rectifier-based medium-frequency AC pooling soft-direct low-cost delivery system for medium- and long-distance offshore wind power. Firstly, the mid-frequency equivalent model of the diode converter is established, and the influence of topology and frequency enhancement on the parameters of the main circuit equipment is analysed; then, the distribution parameters and transmission capacity of the mid-frequency cable are calculated based on the finite element modelling of the marine cable, and the transmission losses of the mid-frequency AC pooling system are then calculated, including the collector losses, converter valve losses, and transformer losses, etc. Finally, an economic analysis is carried out based on a specific example, comparing with the Jiangsu Rudong offshore wind power transmission project, in order to verify the economy of the medium-frequency AC flexible and direct transmission system of the medium- and long-distance offshore wind power using diode rectifier technology. Full article

The evolution of automation has reached marine operations in general and offshore operations in particular. Many facilities in these areas use the Internet of Things (IoT) to consolidate processes and improve data release systems. In addition, the IEC60870-5-104 protocol (IEC104) enables remote data release. This paper introduces and develops a novel IoT architecture that enables the continuous acquisition, evaluation, and release of data between platforms. Continuous data release is based on a dynamic configuration (DC) approach using the IEC104 protocol (DC-IEC104). The proposed approach thoroughly analyzes the structural model and communication process and then proposes a set of design tables according to the information object (type and amount) of the data to be released. In the application case, the data of the photoelectric composite submarine cables were successfully released with an average mean square error of 3.78 and an average processing time of 1.083 s. These results have been proven to be better compared to those obtained using three other approaches for data release. Full article

Space charge injection in polypropylene (PP) significantly weakens the stability of HVDC cables. Impact polypropylene copolymer (IPC) is often used as insulation material for AC cables, but in the DC field, IPC has the problem of space charge accumulation. This is because there is a multi-phase structure inside the IPC to which ethylene monomer was added in the production process, and the difference in physicochemical properties of each phase is an important reason for the accumulation of space charge inside the material. In this work, the vinyl phases and propenyl phases of two types of IPC were separated. The film samples were prepared and tested at 30 °C and 50 °C for DC electrical conductivity, and at 30 °C, 50 °C, and 80 °C for space charge. The experimental results show that the DC conductivity of vinyl phases is significantly higher than that of propenyl phases in both types of IPC. The degrees of mismatch between the DC conductivity of vinyl phase and that of propenyl phase are different in the two types of IPC, and the mismatch degree of DC conductivity is from several times to hundreds of times. The conductivity of the two vinyl samples is ohmic. The conductivity of the two propenyl phases shows nonlinearity under different electric field intensity, and the mismatch degree of the two phases increases with temperature. Compared to untreated IPC, at all test temperatures, the maximum space charge density of the propenyl samples is much lower, which can be reduced by about 1/3 at 50 °C and by about 50% at 80 °C. The density of heteropolar charge produced by impurity ionization in the samples and the depth of electrode injection both decreased. At each temperature, the distortion rate of the electric field in propenyl samples is lower than that in IPC, the distortion rate can be reduced by more than 15%, and the distortion rate can be reduced by nearly half at 80 °C. The charge dissipation characteristic of propenyl samples during depolarization is also optimized compared with IPC samples, the time required for charge dissipation to reach stability is shortened, and the residual charge density in the sample is reduced at the end of depolarization. In addition, the relevance between the variation of DC conductivity of phases and space charge characteristics was discussed according to SCLC (space charge limited current) theory. This work provides a feasible reference for the manufacture of high-reliability polypropylene-based cable material with excellent insulation performance. 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

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

This paper investigates the influence of skin and proximity effects on power losses in segmented power cables using finite element (FE) analysis. Two-dimensional (2D) and three-dimensional (3D) FE models are developed to evaluate the AC-to-DC resistance ratio ($R_{\mathrm{AC}}/R_{\mathrm{DC}}$) in single-, three-, and five-segment cable configurations. Frequencies of 0, 50, 150, and 250 Hz are considered under an infinite lay length (parallel strands) assumption. This study reveals that 2D modeling provides nearly identical $R_{\mathrm{AC}}/R_{\mathrm{DC}}$ values to 3D, with deviations of less than 0.6% at 50 Hz when no twisting is present. This highlights the computational efficiency of 2D models for certain cable designs without compromising accuracy. Furthermore, this paper examines the mesh refinement and sub-conductor geometry (hexagonal packing) of underground cables under full compression assumption. The results underscore the viability of 2D cross-sectional simulations for multi-segment cables, ensuring accurate loss predictions while saving considerable computational resources. Full article

This paper presents a comprehensive three-dimensional (3D) finite-element (FE) study of skin and proximity losses in a five-segment, helically twisted underground power cable. Unlike conventional two-dimensional (2D) analyses—which assume parallel conductors and consequently overestimate eddy current losses—our 3D approach accurately captures the effects of varying lay lengths ($\lambda$). Simulations are performed from 0 Hz (DC) to 50 Hz, showing that while the per-unit-length DC resistance remains unaffected by twisting, the AC resistance can increase significantly depending on the pitch. At 50 Hz, the ratio of AC to DC resistance ($R_{\mathrm{AC}}$/$R_{\mathrm{DC}}$) ranges from about 1.32 for very tight twists ($\lambda =0.1\mathrm{m}$) to nearly 1.72 for gentle pitches ($\lambda =5.0\mathrm{m}$). Further analysis reveals that short lay lengths enhance magnetic field coupling, improving current distribution and partially mitigating losses. To quantify these findings, an exponential-saturation model is proposed to describe $R_{\mathrm{AC}}$/$R_{\mathrm{DC}}$ as a function of lay length, achieving excellent agreement ($R^2\approx 0.996$) with the 3D FE data. These results underscore the importance of considering full 3D geometry in cable design, offering a practical tool for optimizing both mechanical reliability and electromagnetic performance in high-voltage underground applications. Full article

During the long-term operation of the DC grounding electrode of the converter station, there are often hazards such as heating and aging of the coke layer, and burning and corrosion at the connection between the feed rod and the cable, resulting in break problems at the connection between the cable and the feed rod. Currently, the operational status monitoring of grounding electrodes primarily relies on daily tracking of well temperature, humidity, and water level characteristics; periodic testing; and on-site excavation. However, the above methods cannot accurately obtain the breakage location information at the connection between the cable and the feed rod. To address these issues, this paper first analyzes the current distribution law in the feeder rod of the DC grounding electrode. Subsequently, it studies the impact of localized fractures in the DC grounding electrode on the surface potential distribution characteristics. Finally, an Operation State Detection Method (OSDM) based on potential distribution is proposed and validated through case studies, demonstrating high measurement accuracy. The results indicate that OSDM can effectively monitor the operational status of DC grounding electrodes, providing a reference for their maintenance and repair. Full article

Cross-linked polyethylene power cables are widely used in high-voltage DC transmission lines, owing to their good dielectric and physical–chemical properties. However, the production process of XLPE involves cross-linking and degassing, in which the cross-linking process produces a variety of cross-linking by-products, and the changes in the properties of the cable insulation caused by the degassing process are not well understood. XLPE samples were degassed at 90 °C for 7 and 14 days in this paper, and the main by-products were found to be α-methylstyrene, acetophenone, and cumyl alcohol, the contents of which all declined after the degassing treatment. The results show that the space charge density, the leakage current under a high electric field at different temperatures, and the breakdown strength of the XLPE samples all decreased after the degassing treatment. On the other hand, the XLPE sample after 7 days’ degassing had the lowest conductivity and the highest conductance activation, and the space charge density and the charge decay rate as well as the breakdown strength after 7 days’ degassing differed little from the 14-day treated sample, demonstrating that the 7-day degassing treatment at 90 °C would be enough to achieve superior performance. Full article

The direct current (DC) cable serves as the link for energy output in photovoltaic (PV) systems. Its degradation can cause arcs, which easily lead to fire accidents. Locating arc faults, however, is challenging. To cope with it, this paper proposes an arc location method based on time reversal. The method has been tried to locate system fault. However, its application in the arc fault location of photovoltaic systems is seldom discussed and needs further research. For this purpose, the voltage waveforms of an arc fault collected at one of the cable ends is reversed. This transformation derives a symmetrical arc fault signal. Afterwards, the reversed signal is injected back into the cable to trace the fault location, which is a symmetrical process of the arc fault signal travelling from its origin to the detection point. Utilizing the energy-focusing characteristics of time reversal, the position with the highest energy in the derived waveform corresponds to the actual fault location. To verify the proposed method, a DC arc fault test is performed to obtain the wave characteristics. The Paukert arc model is chosen based on the tested result. A PV system containing a DC cable with an arc fault is simulated with Simulink with the affecting factors, i.e., grounded resistance, cable length, fault location and sampling frequency. The simulated results demonstrate that the localization error is within 5% in the worst case. Full article

Energy harvesting technologies are becoming increasingly popular as potential sources of energy for Internet of Things (IoT) devices. Magnetic field energy harvesting (MFEH) from current-carrying components, such as power cables, represents a particularly promising technology for smart grid, infrastructure, and environmental monitoring applications. This paper presents a single-stage AC/DC power converter, a control architecture, and an energy harvester design applicable to MFEH devices. The power converter consists of a MOSFET full bridge that is used to actively rectify the induced voltage at the transceiver while providing a regulated output voltage. The approach is suitable for a broad range of grid power lines, offering a compact power stage that achieves a reduction in component count while active rectification minimizes energy losses, thereby improving thermal management in power electronics compared with the previous research. The experimental results demonstrate that the power converter provides a stable energy source and offers an alternative to self-powering smart grid IoT devices. Full article

A growing interest in offshore wind energy in the Mediterranean Sea has been recently observed thanks to the potential for scale-up and recent advances in floating technologies and dynamic cables: in the Italian panorama, the offshore wind connection requests to the National Transmission Grid (NTG) reached almost 84 GW at the end of September 2024. Starting from a realistic estimate of the offshore wind power plants (OWPPs) to be realized off the southern coasts in a very long-term scenario, this paper presents a novel optimization procedure for meshed AC offshore network configuration, aiming at minimizing the offshore wind generation curtailment based on the DC optimal power flow approximation, assessing the security condition of the whole onshore and offshore networks. The reactive power compensation aspects are also considered in the optimization procedure: the optimal compensation sizing for export cables and collecting stations is evaluated via the AC optimal power flow (OPF) approach, considering a combined voltage profile and minimum short circuit power constraint for the onshore extra-high voltage (EHV) nodes. The simulation results demonstrate that the obtained meshed network configuration and attendant re-active compensation allow most of the offshore wind generation to be evacuated even in the worst-case scenario, i.e., the N1 network, full offshore wind generation output, and summer line rating, testifying to the relevance of the proposed methodology for real applications. Full article