High Voltage Cables Research Articles

Feature extraction based on time-series topological analysis for the partial discharge pattern recognition of high-voltage power cables

In the partial discharge (PD) pattern recognition of power cables, the existing time–frequency features often exert an impact on recognition accuracy because of insufficient discrimination. A novel PD feature extraction and identification method on the basis of time-series topological data analysis (TDA) was proposed in this paper. Firstly, original PD sequence was reconstructed as point cloud in phase space based on optimized symbolic entropy. Then, a PD topological space is constituted with point cloud to extract its persistent homology features. On this basis, persistence diagrams and barcodes were calculated and visually expressed as Betty curves. Finally, Betty curves were input into an optimized 1D convolution neural network (1D-CNN) model to recognize four typical PD patterns and carry out comparison experiments. The visualization produced by t-distributed stochastic neighbor embedding (t-SNE) shows that TDA features possess significant discrimination, experiencing an increase of 11.25% in the overall recognition accuracy and reaching 98.00% compared with original PD sequence and time–frequency features. Meanwhile, the computation cost of the proposed algorithm is optimized within the permissible range for real-time applications.

Research on Harmonic Overvoltage of Cable Sheath on 220kV Side of Electric Railway Traction Station

Abstract The special operation mode of high-speed railway will generate a large amount of harmonics. The harmonics will be transmitted to the 220kV side high-voltage cables through the traction transformer, and harmonic voltages will be generated on the cable sheath, threatening the safe operation of the cables. In this paper, on the basis of the measured harmonic data of the traction substation, a harmonic source model based on the measured data is established, which solves the complex problem of harmonic source modeling and can accurately reflect the actual operating conditions of high-speed trains. On this basis, the harmonic voltage characteristics of the cable sheath on the 220kV side of the high-speed railway under the three working conditions of traction, regenerative braking and inertia are simulated and calculated, and the effects of cable length, cable grounding method, and harmonic current parameters on the harmonic voltage are explored. Affect the law. The results show that under different operation modes of high-speed rail, the harmonic voltage of the sheath far exceeds the normal operation of the power frequency, and the maximum value of the harmonic voltage of the cable sheath can reach 454V under the traction condition; Under working conditions, the overvoltage of the metal sheath is greatly affected by the grounding method of the cable, the length of the cable and the harmonic current content. The above research results have important reference significance for the safe operation of electrified railways.

Effect of hindered phenolic antioxidants on crosslinking characteristics of low-density polyethylene initiated by peroxide

Hindered phenolic antioxidants are the most prevalent antioxidants used in crosslinked polyethylene (XLPE) insulating materials of high-voltage (HV) cables. Doping antioxidants is conducive to delaying the low-temperature pre-crosslinking, but decreases final crosslinking degree. In order to comprehensively reveal the effect of hindered phenolic antioxidants on the crosslinking characteristics of XLPE insulating materials, four kinds of insulating materials doped with different hindered phenolic antioxidants are studied by experiment and simulation methods. The results demonstrate that antioxidant 300 is better for delaying low-temperature pre-crosslinking of insulating materials, but negative for maintaining high crosslinking efficiency and degree. Although insulating materials with antioxidant 1010 have higher crosslinking degree, it is poor to delay the low-temperature pre-crosslinking. Notably, antioxidant 245 with phenolic hydroxyl of lower bond dissociation energies can delay the low-temperature pre-crosslinking to some extent, meanwhile, crosslinking efficiency and degree of XLPE are still higher. Notably, the crosslinking characteristics of XLPE insulating materials are closely related to molecular structure of antioxidants, including functional group and ortho-substituents. Comprehensively considering the demands of delaying low-temperature pre-crosslinking and maintaining high crosslinking degree of insulating materials, antioxidant 245 is the better choice. This study provides a theoretical guidance for the choice of hindered phenolic antioxidants used for HV cable insulating materials.

Electric Field Characteristics of HDPE-NR Biocomposite Under Breakdown Condition

It is critical to develop new insulating materials that can improve the performance of next generation high voltage cables for creating future electrical networks. The high electric field reduces the resistance of solid insulation and produces partial discharge through imperfections in a dielectric, causing the dielectric to age and eventually fail. Thus, this project seeks to analyse the electric field intensity of High Density Polyethylene (HDPE) in breakdown condition when added with 10g, 20g and 30g of different types of bio-filler such as coconut coir fibre, pineapple leaves fibre, and oil palm empty fruit bunch. This can be achieved by creating a two-dimensional (2D) axisymmetric electrostatic model by using the Finite Element Method Magnetics (FEMM) 4.2 software. The results showed that the unfilled HDPE biocomposites have a higher electric field intensity than 10g, 20g, and 30g biocomposite. This indicates that the maximum electric field intensity changes according to the permittivity and voltage of the bio-filler under breakdown conditions. As a result, the maximum electric field intensity was much lower for HDPE added with a 20g of the pineapple leaves fibre. Hence, pineapple leaves fibre was the best composition as it tends to improve the dielectricproperties since it has a lower electric field intensity at the top electrode as compared to other compositions.

Analytical Computation of Thermal and Electrical Issues in E-Mobility Cabling Network

The demand for pollution-free transportation is increasing daily worldwide due to increasing concerns about global warming, greenhouse gas emissions, and the depletion of fossil fuels. In e-mobility, electric vehicles (EVs) have received massive popularity due to their performances and efficiencies compared with IC engine vehicles in recent decades. Cables play an essential role in delivering electric power to the different electrical components system from the battery source of vehicles. Electrical insulation is the backbone of the power cable, and its state is usually used to reflect the healthy condition of this cable and any electrical networks. Deterioration of the cable during normal operation is a major concern. Usually, electric cables receive less maintenance as compared to other electrical components in EVs. Due to the many stresses, the cable insulation must constantly withstand better connectivity between different parts in e-mobility. In the analytical method, the solution obtains known elementary functions by integrating a partial differential equation better to understand the variation of thermal and electrical stresses. This paper studied the high voltage cabling network of electric vehicles and the analytical method used for computing conductivity, temperature, and electrical stress distribution in electric vehicle cabling networks by including the higher vehicle ambient temperatures. The thermal and electrical stress maximizes at the conductors' surface and gradually reduces the function of the radial distance.

High Voltage Cable Fault Location Technology Based on Traveling Wave

High voltage cable line is an important part of power grid; its stable operation is of great significance to urban power system. This paper proposed a high voltage cable insulation monitoring system using traveling wave. The travelling wave data are collected by high precision satellite timing signal and an on-line fault location system for high voltage cable is designed.

The Lifetime Prediction and Insulation Failure Mechanism of XLPE for High-Voltage Cable

The performance parameters and service life of the insulation layer of high-voltage cables are the key to ensure safe cable operation. Through extracting the mechanical parameters of high voltage cable insulation layer under different thermal aging temperatures, a normal linear regression model is established to predict the service life of high voltage cables. Meanwhile, the physicochemical characteristics such as microscopic morphology and molecular structure changes of the cable insulation layer are analyzed, the dielectric properties and breakdown field strength under ac condition are tested and the macroscopic electrical properties of the insulation layer are studied, and the insulation failure mechanism is further analyzed. The experimental results show that the elongation at break retention rate of cross-linked polyethylene (XLPE) increases slowly with the aging time, and then decreases rapidly when it reaches 50% of the initial elongation at break retention rate. The normal linear regression prediction model is established based on the Arrhenius formula, and it can be obtained the life endpoint of XLPE high voltage cable about 65 years at an operating temperature of 70 °C. Further analysis, under the action of heat and oxygen, the crystal zone structure of cable insulation is seriously damaged, and the carbonyl index is significantly increased. Accordingly, when the aging failure point is reached, the dielectric permittivity and dielectric loss of insulation are significantly increased, and the breakdown performance is significantly decreased. The work has an important guiding significance for insulation condition assessment and life prediction of high voltage cable.

Annealing effect on the crystallinity characteristics of XLPE from High-voltage Cables

The thermal effects during the cable operation brought various changes in cable insulation, strongly affecting the cable’s long-term behavior. In this study, a new and seven-year serviced 110 kV XLPE cable was taken, and the insulation layer was peeled and thermally aged at 115 for various 60, 120, and 180 days. Then, they were annealed at 90 to 115°C with a gap of 5°C, respectively. The gel content and differential scanning calorimetry (DSC) were measured. The results show that the 60 and 120-day aging tests promote the crystallization of XLPE and show a higher recrystallization point and crystallinity, while the 180 days aging test brought an opposite change. After the annealing process, melting point and crystallinity increase with the increasing annealing temperature. Before they reached the highest values, 60-day-aged peels showed higher the two factors than the fresh peels, with a slight difference to 120-day-aged peels, but 180-day aged showed the lowest values. However, the annealing process results in a lower melting point and crystallinity when the temperature exceeds the optimum point. Finally, it was found that the crystallization characteristics of the aged XLPE peels could be improved if the annealing was done at proper temperatures.

Research on the selection of high voltage submarine AC cables for long distance offshore wind farm

With the increase distance of offshore wind farm, the investment proportion of high-voltage delivery submarine cable in the whole project is gradually increasing, so the reasonable selection of cable delivery scheme becomes more and more important. In this paper, for different scales of offshore wind farms, the preliminary selection basis of two delivery schemes of AC high-voltage and flexible DC is proposed, and the economic and technical comparison principles of different AC delivery schemes are further analyzed with engineering example. In general, for medium-sized offshore wind farms, if the AC high-voltage transmission scheme is used, a reactive power compensation station can be set in the middle of the cable to improve the current distribution on the cable.

Anchor Fault Identification Method for High-Voltage DC Submarine Cable Based on VMD-Volterra-SVM

This article introduces a new method for identifying anchor damage faults in fiber composite submarine cables. The method combines the Volterra model of Variation Mode Decomposition (VMD) with singular value entropy to improve the accuracy of fault identification. First, the submarine cable vibration signal is decomposed into various Intrinsic Mode Functions (IMFs) using VMD. Then, a Volterra adaptive prediction model is established by reconstructing the phase space of each IMF, and the model parameters are used to form an initial feature vector matrix. Next, the feature vector matrix is subjected to singular value decomposition to extract the singular value entropy that reflects the fault characteristics of the submarine cable. Finally, singular value entropy is used as a feature value to input into the Support Vector Machine (SVM) for classification. Compared with Empirical Mode Decomposition (EMD) and Ensemble Empirical Mode Decomposition (EEMD), the proposed method achieves a higher fault identification accuracy and effectively identifies anchor damage faults in submarine cables. The results of this study demonstrate the feasibility and practicality of the proposed method.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.

Effect of thermo-oxidative aging on thermal elongation performance of XLPE insulation for high-voltage cables

The thermal elongation of cross-linked polyethylene (XLPE) insulation for high-voltage cables is an important factor for evaluating the high-temperature mechanical performance, which is an important parameter included in the testing standards of the power cable insulation. Previous studies have found that the thermal elongation of XLPE insulation for high-voltage cable depends on the cross-linking degree, but have not dealt with the effect of the thermo-oxidative aging during the thermal elongation test. In this paper, the thermal elongation experiments of the XLPE samples compounded with different kinds of antioxidants were carried out under both air and nitrogen atmospheres. The molecular structure changes of the XLPE samples after thermal elongation under air atmosphere were examined by gel content, FTIR spectra and X-ray diffraction. The oxidation induction periods were also measured to analyze the antioxidation performance of the phenolic antioxidants and study its contribution to the thermal elongation performance. The results showed that the XLPE samples underwent thermo-oxidative aging in the thermal elongation test under air atmosphere at 200 °C. It caused that the thermal elongation properties can not accurately reflect the cross-linking degree of the original XLPE samples, but has a strong correlation with the gel content of the aged samples. Antioxidants can inhibit the thermo-oxidative aging effect on the network structure, leading to a slower uptrend of elongation under the air atmosphere. This indicates that the thermal elongation performance of XLPE insulation is determined by the synergistic effect of the network structure and the antioxidation performance, and this can provide reference significance for optimizing the evaluation methods of high-voltage cable XLPE insulation performance.

Fault Diagnosis of HV Cable Metal Sheath Grounding System Based on LSTM

At present, the metal sheath of high voltage (HV) cables generally adopts the cross-bonded grounding method, which brings many types of faults and challenges the monitoring and diagnosis of the operation status of the cables. In order to effectively diagnose various types of faults in the metal sheath grounding system of HV cables, this paper proposes a fault diagnosis method for the metal sheath grounding system of HV cables based on long and short-term memory (LSTM). Firstly, the grounding system model of HV cable metal sheath is established. Secondly, the sheath currents of four faults are analyzed. Based on the sheath current amplitude ratio and phase difference of the same loop and the same grounding box, 14 feature vectors reflecting the operation state of the metal sheath grounding system are constructed. Then, the operation state of 18 kinds of metal sheath grounding systems is simulated, and the fault database is established. Finally, the LSTM algorithm is used to accurately identify the fault of HV cable grounding system. The results show that the LSTM algorithm can effectively diagnose and identify the faults of the HV cable metal sheath grounding system, and the accuracy rate is 100%.

A computational modelling of carbon layer formation on treeing branches

Polymeric insulation employed in electrical power industry undergo irreversible and unpredictable ageing due to partial discharges (PDs). In particular, the dielectric properties of polyethylene (PE) used in high voltage cables are often compromised by the formation of electrical trees. In this work we assume that the propagation of treeing channels involves the injection of carbonic material into the gas interacting with the surface of the defect. Experimental characterizations proved that, in certain conditions, disordered graphitic carbon can form in some areas of the electrical trees, thus increasing surface conductivity and inhibiting PDs. The chemical mechanism involved in this process is yet to be clarified. Here we propose a model for this process. By means of a series of molecular dynamics simulations, we show how the chemisorption of gaseous molecules on a PE surface can lead to a bidimensional carbonic structure. The characterization of the density of states of such systems suggests that the presence of pure carbon adsorbed on the polymer causes an increase in surface conductivity.

Numerical Investigation on Thermal and Electrical Stress in Electric Vehicle Cabling Network

Global warming and an impending energy problem have compelled nations to become greener and cleaner. Worldwide, interest in electric vehicles (EVs) is growing as a result of rising gasoline prices and environmental concerns. The need for electrical components and cabling networks is expanding along with the demand for electrified vehicles. The complexity of vehicle electrical, electronics, and control circuits is also rising. There are many wire and cable performance issues in modern e-mobility, including limited space, vibration, high-temperature variation, unfriendly fluids, and rising data transmission requirements. Thus, it is important to study and evaluate the thermal and electrical stresses in the electric vehicles cabling network to avoid insulation failure, which causes fire accidents in the electric components of EVs. An EV's entire electrical system gets hotter, and insulation strength is affected by both temperature and the electrical field. The insulation system is one of the most important components in any electrified vehicle. From a design and protection perspective, the computation of electric potential distribution and electric field within and around the cables of electric vehicles is very important. The strong non-linear dependency of the electrical conductivity of the insulation material on prevailing electrical stress and temperature makes the field problem not only coupled but also non-linear. Finite Difference Numerical (FDM) is used for non-linear field computation. In this paper, different electric vehicle cabling network layouts were studied and listed the challenges. Chosen the high voltage cables of electric vehicles from the cabling network and numerically computed the conductivity, temperature, and electrical fields of cable.

Effect of Polycyclic Aromatic Compounds on Electrical Treeing Growth in XLPE Insulation

This article focuses on the effect of polycyclic aromatic compounds (PACs) on the electrical tree of cross-linked polyethylene (XLPE) insulation for high-voltage (HV) cables. The XLPE insulation samples with or without PACs are prepared for electrical treeing degradation at constant and cyclic temperatures. The results show that the growth of the electrical tree within the XLPE/PACs insulation is retarded. The partial discharge (PD) amplitudes of XLPE/PACs insulation are significantly decreased during the treeing process compared to XLPE insulation. Furthermore, under cyclic temperature conditions, the tree growth of XLPE/PACs composites stagnates as the temperature decreases from 90 °C to 25 °C. Even when it rebounds to 90 °C, the treeing degradation of XLPE/PACs insulation is still retarded, resulting from a significant weakness of PD. The results show that the XLPE/PACs composites exhibit a greater electrical treeing resistance. Based on density functional theory (DFT), analysis of the excitation characteristics and density of states (DoS) reveals that the PACs absorb photon energy to prevent damage to insulation. In contrast, the excited PACs result in a cross-linking reaction to XLPE and introduce electron and hole traps, which capture hot electrons. The cross-linking product acts as localized states of electron traps and hole traps, which capture the high energy carriers during treeing. In summary, the PACs retard the growth of electrical trees and improve the insulation performance.

Impact of heterogeneous cavities on the electrical constraints in the insulation of high-voltage cables

1. Khouildi E, Attia R, Chtourou N. Numerical modeling of the electric field and the potential distributions in heterogeneous cavities inside XLPE power cable insulation. Journal of Electrical and Electronics Engineering. 2016; 9(2):37-42. https://www.proquest.com/openv.... Google Scholar

Dynamics of Phonon-Assisted Holes Trapping and Transport over Chemical Defects in Polyethylene.

Charge trapping and transport over chemical defects in polyethylene have significant impacts on its electrical and dielectric properties. However, the dynamics of this phenomenon and its underlying mechanisms remain unclear. To understand this fundamental aspect, we conducted a time-domain ab initio nonadiabatic molecular dynamics study of phonon-assisted holes dynamics in polyethylene over C═O and C-OH defect states. Our results suggest that the hole transfer and energy fluctuations substantially depend on temperature and local morphology. When the temperature decreases from 300 to 100 K, the hole transfer efficiency and the energy fluctuations are severely suppressed due to the weakened interactions between holes and phonons. Furthermore, amorphous polyethylene exhibits a severe suppression of the hole transfer process compared to crystalline polyethylene. An explanation for the influence of morphology on the hole transfer process can be found in the differences in the hole-phonon coupling and the electronic coupling between two chemical defect states in crystalline and amorphous polyethylene. Advancing the fundamental understanding of the dynamics of hole transfer over chemical effects in polymers is a key to improving their insulating properties for the next-generation high-voltage cables.

Electric field regulation of polypropylene insulation for high voltage DC cables

High voltage cable is the key factor to determine the quality and capacity of power transmission. Polypropylene has widely attracted more attention because of its excellent heat resistance, insulation and green environmental protection, and it is used as cable material. Polypropylene insulation material for high voltage cable needs to bear pulsed voltage and the DC rated voltage, which can easily cause electric field to be distorted and lead the space charge to be accumulated. Meanwhile, the change of cable temperature will also affect the conductivity of insulating material and promote the accumulation of space charge, resulting in the distortion of internal electric field of insulating material and the initiation and growth of electric tree. Therefore, it is necessary to regulate the electric field of high voltage cable so as to suppress the deterioration phenomena such as electric field distortion, partial discharge and electrical demoralization. In this work, the theory and method of regulating DC electric field of polypropylene insulation of high voltage cable is first introduced. Then the main direction of electric field regulation is presented. Finally, the application prospect of polypropylene cable insulation is also put forward.

Electrical Tree Image Segmentation Using Hybrid Multi Scale Line Tracking燗lgorithm

Electrical trees are an aging mechanism most associated with partial discharge (PD) activities in crosslinked polyethylene (XLPE) insulation of high-voltage (HV) cables. Characterization of electrical tree structures gained considerable attention from researchers since a deep understanding of the tree morphology is required to develop new insulation material. Two-dimensional (2D) optical microscopy is primarily used to examine tree structures and propagation shapes with image segmentation methods. However, since electrical trees can emerge in different shapes such as bush-type or branch-type, treeing images are complicated to segment due to manifestation of convoluted tree branches, leading to a high misclassification rate during segmentation. Therefore, this study proposed a new method for segmenting 2D electrical tree images based on the multi-scale line tracking algorithm (MSLTA) by integrating batch processing method. The proposed method, h-MSLTA aims to provide accurate segmentation of electrical tree images obtained over a period of tree propagation observation under optical microscopy. The initial phase involves XLPE sample preparation and treeing image acquisition under real-time microscopy observation. The treeing images are then sampled and binarized in pre-processing. In the next phase, segmentation of tree structures is performed using the h-MSLTA by utilizing batch processing in multiple instances of treeing duration. Finally, the comparative investigation has been conducted using standard performance assessment metrics, including accuracy, sensitivity, specificity, Dice coefficient and Matthew’s correlation coefficient (MCC). Based on segmentation performance evaluation against several established segmentation methods, h-MSLTA achieved better results of 95.43% accuracy, 97.28% specificity, 69.43% sensitivity rate with 23.38% and 24.16% average improvement in Dice coefficient and MCC score respectively over the original algorithm. In addition, h-MSLTA produced accurate measurement results of global tree parameters of length and width in comparison with the ground truth image. These results indicated that the proposed method had a solid performance in terms of segmenting electrical tree branches in 2D treeing images compared to other established techniques.