The increase in offshore wind power transmission capacity and the development of far-shore projects mean that cables in converter stations must carry higher loads in increasingly compact layouts. Proper cable arrangement is essential for ensuring the operational safety of cables and improving space utilization in converter stations. The paper presents a three-dimensional simulation model for analyzing the spatial distribution of loss density under complex installation configurations. The effects of different installation configurations and phase-angle matching schemes on the loss densities of the aluminum screen and conductive graphite coating were analyzed based on actual cable arrangements and the combined effects of internal and external interference. Ultimately, arrangement principles for cables within compact converter stations under different screen-bonding designs are proposed. The study found that adjacent cables should be arranged as perpendicular as possible and bent at intersection points. The maximum loss density is reduced by a factor of 9.13 compared with the parallel arrangement. If a parallel arrangement is unavoidable, proper phase-angle matching between adjacent cables should be ensured. Different phase-angle configurations can produce a maximum-to-minimum loss-density ratio of up to 31.15. This research provides references for the compact design of internal cables in flexible DC converter stations.

Real-time vibration monitoring for oil-immersed transformer windings is critical for power grid digitalization, yet traditional fluid-structure interaction (FSI) simulations remain computationally prohibitive. This paper proposes a Domainless fluid inertia equivalent(DFIE) method that eliminates flow domain meshing by discretizing fluid velocity potential and added mass directly on the winding boundary. The method couples with structural dynamics to form a simplified 'structure-inertia' equation, bypassing global flow field calculations. Compared with the global FSI method, DFIE reduces the calculation time by 99.38% and the memory occupation by 26.43% while maintaining the calculation accuracy (error within 5%), which breaks through the core bottleneck that the traditional method's 'accuracy-efficiency' is difficult to balance. The multi-condition vibration test carried out on the customized 10 kV oil-immersed distribution transformer experimental platform further verifies the effectiveness of the method : the average relative error of the vibration acceleration amplitude between the simulation and the experiment is 3.35% (within 3.5%). Crucially, the direct sensor placement on the transformer coil surface resolves prior validation gaps. The method enables rapid multi-condition vibration evaluation for dynamic stiffness optimization and fault early-warning model training, directly addressing measurement-validated engineering solutions. By breaking the 'accuracy-efficiency' trade-off, DFIE provides a practical path for real-time transformer monitoring in smart grids.

The compact design of the offshore converter station increases the density of high voltage cable laying. To ensure the stable operation of the cable, the outer sheath should be coated with a graphite conductive coating (GCC) after laying to test its insulation. The grounding configurations applicable to GCC coated cable have not yet been clarified. Therefore, a new method is proposed to analyse the electromagnetic interference (EMI) level of high voltage cable under the condition of external GCC. Combined with the actual working conditions of the flexible DC converter station, a finite element model of high voltage cable supporting flexible grounding configurations is constructed from capacitive and inductive coupling perspectives. The error margin is approximately 1% compared to the calculation results of the equivalent circuit method. The influence mechanism of different grounding configurations on the EMI of aluminium metal sheath (AMS) and GCC is investigated. The results show that the capacitive coupling mainly affecting the interference voltage and inductive coupling mainly affecting the interference current. The actual project should ensure that at least one end of the AMS protective grounding, and GCC at least one end of the direct grounding, to avoid abnormal EMI phenomenon during cable testing and operation.

Sheath currents in HV cable systems often exceed standard values, while no faults were found. Existing fault diagnosis methods for the grounding system heavily rely on theoretical models and neglect the shared grounding points of multiple cable circuits, resulting in unsatisfactory practical performance. This paper establishes theoretical models of the grounding system in various states of cable circuits with shared grounding grids. Whist differences among the magnitudes of the three phase load currents are assumed negligible, the distribution characteristics of the sheath currents are analyzed and three kinds of correlations between the measured sheath currents and the configuration of the sheath grounding systems are proposed and investigated. A fault diagnostic model based on graph attention networks (GATs) is established with the combination of the three relationships as prior knowledge, enabling the diagnosis of the grounding system without reliance on theoretical models or circuit parameters. The model is validated by field data and simulation data, which demonstrate that the four metrics of the fault diagnostic model are above 90%. The incorporation of GATs and prior knowledge enhances the model’s accuracy by 14.41% in comparison with that of the traditional fully connected neural network model.© 2017 Elsevier Inc. All rights reserved.

Dynamic thermal rating (DTR) is an effective strategy that can enlarge transfer capacity of cables and enhance renewable distributed generators (RDGs) accommodation in favorable meteorological conditions. However, with higher penetration of RDGs, distribution networks face voltage rise challenge, which in turn could hinder further implementation of DTR. At the same time, higher carrying-currents aggravate losses of life (LOL) of cables. To deal with such issues, an optimal model is proposed, which aims to minimize the operation cost by comprehensively taking advantages of DTR, network reconfiguration and active controls such as energy storage and reactive power compensation devices, so as to effectively enhance RDGs accommodation as well as keep the LOL of cables at a relative low level. Accordingly, a model transformation method based on second-order cone relaxation, linearization of variables product and piecewise linearization is designed, the original non-convex nonlinear model is then transformed into a mixed integer second-order cone programming (MISOCP) model by convex processing of non-convex sources, thus reducing the computational complexity. Numerical results demonstrate that the proposed model can effectively enhance RDGs accommodation as well as reduce the LOL of cables.

Researching the measurement of DC total electric field with space charges (Poisson field) can help establish a monitoring system for the electromagnetic environment of UHVDC transmission lines and protect the health of the ecological environment. This paper proposes a DC total electric field optical measurement method based on the Pockels effect and probe self-rotation modulation. It can address the issues of internal charge drift and external charge accumulation in traditional optical probes when measuring DC electric fields with space charges. Theoretical analysis was conducted on measurement under probe rotation, and the optical modulation system was integrated into a probe with dimensions of 60 mm x 30 mm x 20 mm. A self-rotating platform for the probe was designed, and the influence of rotation mode on the results was analyzed. It was found that the sensitivity was higher when using the horizontal-horizontal mode. The signal processing system was tested, showing that the probe retained around 50 % of its original output when rotating at low speeds (frequency 1-3 Hz), fully meeting the measurement requirements. The test platform has been constructed, and the probe's sensitivity was assessed under an AC electric field and validated under a DC electric field. Finally, the optical method proposed in this paper was used to measure the DC total electric field with space charges under a small model of a unipolar HVDC transmission line. Five locations under the line were selected as measurement points, and the results were compared with those obtained from a field mill probe and numerical simulation. This comparison indicates that the proposed method agrees with experimental and simulation results. The average sensitivity of the self-rotating optical probe was 3.71 mV/(kV/m). The error did not exceed 5 % in high-field strength areas (above 20 kV/m) and was also controlled within 15 % in low-field strength areas (below 20 kV/m).

Current thermal analysis of power equipment predominantly employs electromagnetic-thermal indirect coupling methods. While accounting for temperature-dependent material conductivity necessitates iterative electromagnetic-thermal field calculations, existing approaches suffer from cumbersome data extraction and mapping during cross physical field coupling. To address this limitation, this study proposes a direct electromagnetic-thermal coupling method that integrates governing equations of electromagnetic and thermal fields through discretized matrix coupling coefficients, enabling simultaneous updates of both fields via iterative matrix solutions. Applied to oil-immersed transformers, the method incorporates temperature-dependent winding conductivity into an electromagnetic-thermal-fluid coupled framework. Case studies demonstrate that this direct coupling strategy reduces iteration cycles in multi-physics simulations, significantly improving computational efficiency for winding temperature rise analysis.

With the development of deep-sea wind power, the temperature hotspots of submarine cables in J-tubes are getting increasing attention. Currently, the relevant standards do not provide a thermal rating method for such cable sections, and the only studies are difficult to apply in practice. This study derived an analytical solution for calculating the derating in ampacity of submarine cables within J-tubes. The proposed approach is efficient and readily integrated with IEC-related standards. Initially, an indoor experiment was conducted to validate the correctness of the analytical model. Subsequently, a numerical example utilizing an actual HVDC submarine cable is presented, demonstrating increased cable conductor temperature within the J-tube and a corresponding reduction in ampacity. A derating factor is employed to quantify the extent of ampacity reduction, which is a function of the J-tube length, outer diameter, ambient temperature, wind speed, and solar radiation intensity. It turns out that once the J-tube air section's length exceeds approximately 60 times the cable outer diameter, the transmission circuit ampacity can be based on the value installed in the infinite J-tube. Furthermore, factors resulting in substantial cable ampacity reduction, such as high solar radiation intensity, may yield a derating factor approaching 0.6.

Insulating oil is the primary insulating medium of converter transformers, which may be subject to the influence of direct current superimposed with impulse voltage under working conditions. In this paper, a two-dimensional axisymmetric fluid simulation model of streamer discharge in mineral insulating oil is established based on the hydrodynamic drift-diffusion model. The simulation investigates the initiation and development of needle-plane streamer discharge in mineral insulating oil under short oil gap conditions. The characteristics of streamer discharge are analyzed in mineral insulating oil under various conditions, including different pulse, different voltage amplitude, and different direct current superimposed with impulse voltage conditions to provide theoretical and technical reference for the design of insulation of converter transformers.

The increasing permeability of renewable energy render the traditional static security analysis method based on deterministic load flow no longer applicable. In power systems with uncertain renewable energy sources, probabilistic load flow (PLF) analysis must be conducted to achieve static security analysis of the power system by examining voltage and branch load flow during the operation. This paper proposes a PLF calculation method based on C-type Gram-Charlier series expansion and cumulant (CGC-CM), which can determine the distribution characteristics of bus voltage and branch transmission power. The proposed method solves the problem of negative values in the calculation of PLF for the results of the traditional A-type Gram-Charlier series expansion (AGC) method. Additionally, three typical wind and photovoltaic power generation output scenarios are created using k-means clustering, followed by an assessment of the static security of the power system. In this paper, the accuracy and efficiency of the algorithm is verified using the IEEE30 test system. Besides, it is observed that the static stability of the power system decreases with an increase in wind and photovoltaic power output. Subsequently, a real power system model was established and demonstrated that the branch capacity increase can improve the stability of the system operation.

Due to the enclosed air interlayer in the J-tube section, it has the potential to limit the current-carrying capacity of offshore wind farm export cables. The standard calculations outlined in the IEC guidelines are deemed inadequate for this unique laying method. Conducting fluid simulations can be time-consuming and challenging to implement in practical engineering scenarios. This article introduces a rapid calculation approach for determining the current-carrying capacity of submarine cables in J-tube sections, utilizing a semi-empirical correlation formula for natural convection in a vertical enclosed annular space and an axial heat transfer model for submarine cables. A comparative analysis between the proposed method and thermal-fluid coupling numerical simulations demonstrates the effectiveness of the proposed approach.

The ion flow field of UHVDC transmission lines is greatly affected by wind, especially in high-altitude areas where the regional and gradient differences in wind speed are significant. To accurately provide the required wind speed verification values for line parameter design, a numerical simulation method based on Weibull-WSE-UFEM is proposed in this paper. Weibull function is used to construct the probability distribution of wind speed in the studied area based on real data, and the maximum value within the appropriate range is selected as the wind speed verification value for the location of the wind speed sensor. Wind Shear Exponent (WSE) is used to expand the verification values at different positions in the vertical direction. Upstream Finite Element Method (UFEM) is used to calculate ion flow field and the verification values are used as the input wind speeds in different height nodes. The method was applied to a real high-altitude UHVDC transmission line case and the theoretical minimum height of line to ground was obtained. The results indicate that the method has certain guiding significance for the design of UHVDC transmission lines in high-altitude areas.

MATLAB software is used to simulate the circulation of the gas insulated metal enclosed transmission lines (GIL) pipe corridor system and the ground potential. The 500 kV GIL grounding system and the shell circulation model are established. The analysis shows that the shell circulation decreases with the increase of the resistance of the ground lead, while the shell potential to the ground increases, and both values tend to be saturated. Under the condition of the same resistance of the ground lead, the shell circulation and potential to the ground increase linearly with the increase of line length and mutual inductance, and the ground lead impedance increases with the increase of line length. Through the simulation analysis of the shell potential to the ground of the long-distance GIL of the single phase, it is obtained that the shell potential to the ground is lowest in the center of the shell and tends to 0, and highest at both ends, showing a "V" shape distribution. When the total length of the line is constant, the more the number of segments of the shell, the lower the shell potential to the ground at both ends. It provides the basis for practical engineering design.

As an important indicator of the electromagnetic environment of UHVDC transmission lines, the ion flow field needs to be quickly calculated and updated in case to meet the requirement in building a digital twin of the power transmission system. This paper is based on the UFEM and starts from two aspects: electric field intensity convergence and charge density convergence. a) An adaptive iteration factor for charge density update is introduced, which can automatically control the iteration speed according to the change degree of electric field intensity, ensuring the rapid and stable update of charge density. b) On this basis, a half-error term is added to the charge density update formula. This controllable disturbance has little impact on the convergence of the charge density, but can greatly accelerate the convergence of the electric field intensity. Their combined effect greatly reduces the iteration steps required for the entire solution. A coaxial cylindrical model with analytical solutions and a real +/- 800 kV UHVDC transmission line project with test results are used to verify the method. In terms of accuracy, the numerical calculation results are exactly the same as the analytical solutions and are basically consistent with the test results. In terms of speed, compared with traditional fixed factors, after using the adaptive iteration factor, the iteration steps are reduced by up to 75%. In addition, after adding the half-error term, the iteration steps are further reduced by 32%. This method can strongly support the application of digital twin technology in power transmission.

海上风电场送出线路从升压站穿出首先需经过散热环境较差的J型管段,目前针对该区段海底电缆载流量的计算主要采用数值模拟法,而三维流体仿真计算非常耗时,因此难以推广使用.该文基于基本热分析方法提出了J型管段海底电缆径向-轴向传热解析模型,考虑温度沿轴向分布的差异,实现J型管段海底电缆载流量的快速计算.在计及导体电阻率随温度变化情况下,利用数值仿真软件建立海底电缆 J 型管系统三维热-流耦合数值模型,并与径向-轴向传热解析模型进行了对比计算.最后基于两种方法分析了 J型管外径、太阳辐射强度和环境温度对 J型管段海底电缆缆芯最高温度的影响规律.结果表明,J 型管段海底电缆缆芯最高温度与太阳辐射强度和环境温度存在明显的线性关系,而 J型管外径与海水温度对 J型管段海底电缆缆芯最高温度影响较小,且解析法与数值仿真计算结果误差在 5%以内.该文所提出针对J型管段海底电缆载流量计算的解析法高效准确,具有较好的工程应用价值.

The Jiles Atherton hysteresis model (J-A model) is a mainstream magnetization model that describes the hysteresis phenomenon of ferromagnetic materials. It is widely used in the field of magnetic modeling, which can reflect macroscopic magnetization phenomena and calculate micro energy loss changes. This article derives the characterization form of J-A theory based on the magnetization mechanism and energy conservation equation, and conducts simulation calculations on different material samples. The simulation results are compared with the measured magnetic characteristics data of the material, verifying the effectiveness and accuracy of the J-A model, which can more accurately simulate the static hysteresis loop of ferromagnetic materials.

This paper quantitatively analyzes the impact of induced current and leakage current on GIL equipment by establishing a GIL shell circulating current calculation model. In addition, the GIL grounding system and shell circulation model were established. When the grounding spacing is less than 2000 m, the shell circulation and shell potential will increase significantly with the increase of grounding spacing, and the GIL shell potential shows a “U”-shaped distribution with low middle and high end. The potential can be reduced to a single digit to ensure the safety of staff.

Gas insulated transmission line (GIL) is widely used for large-capacity power transmission in complex environment, and has the characteristics of long distance and totally enclosed structure. When the insulation fault occurs inside GIL, its metal shell structure makes it more difficult to monitor through optical, electrical and other physical quantities. Considering the rapidity and accuracy of positioning, the propagation of sound waves along the GIL sheath is a commonly used method in GIL on-site PD testing and running state online monitoring for fault positioning. This paper establishes a high-pressure GIL acoustic propagation simulation model based on pipe acoustics theory, analyzes the frequency dispersion and mode distribution of acoustic waves along the GIL shell, determines an appropriate fault location strategy based on the propagation velocity and attenuation of the selected acoustic wave mode, and carries out experiments to verify it. The results of the research show that the low order bending wave F(1,1) propagated along the GIL shell has good positioning characteristics, and the propagation velocity conforms to the dispersion curve distribution. By taking into account the attenuation and delay of the acoustic wave passing through epoxy insulators or expansion joints in the fault localization strategy, the localization accuracy can be improved by 60%. And this positioning strategy was verified to be effective in the GIL insulation fault localization test conducted in the field.

When gas insulated transmission line (GIL) is applied to long-distance transmission in urban underground pipe gallery, it will generate overvoltage due to capacity rise effect, which may threaten the insulation safety of equipment. However, at present, there is little research on voltage distribution along long-distance GIL. In this paper, the transmission line distributed parameter model is used to establish the voltage distribution calculation model along GIL, and the voltage distribution characteristics along GIL at different distances and voltage levels are calculated by taking typical transmission voltage levels as examples. The results show that the maximum value of GIL no-load line overvoltage occurs at 1 / 4 of the electromagnetic wavelength on the line from the head end of the line, and the line voltage increases with the distance when it is within 1/4 of the wavelength from the head end of GIL line. Through the analysis of overvoltage distribution of GIL lines with typical length, it is found that within 20 km, the increase rate of GIL end overvoltage is lower than 0.03