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Cable termination fault is one of the most important problems for high voltage underground cable lines (HVUCL). Harmonic current (HC) and the sheath current (SC) are causes of cable termination faults of HVUCL. The sheath voltage (SV) of cable increases due to SC and HC also. So, the electroshock risk for human occurs. In this study, cable termination faults are examined for long HVUCL that is connected to electric network with high harmonic distortion rate. In literature, solid bonding (SB) and sectional solid bonding (SSB) methods are used to reduce harmonic distortion rate and SC effect in HVUCL. However, when SB and SSB methods are used for bonding of long HVUCL, harmonic distortion limit and touch voltage limit are exceeded. Therefore, the modified SSB (MSSB) method is developed for bonding of long HVUCL. SV of HVUCL should be known to use MSSB for bonding of long HVUCL. Then SV of HVUCL is forecasted by using artificial neural network and hybrid artificial neural networks (HANN) before the long HVUCL is installed. MSSB parameters should be optimized, so that optimization methods are used for optimization of MSSB and HANN. When MSSB method is used for bonding of long HVUCL, harmonic distortion limit and touch voltage limit are not exceeded under high harmonic distortion conditions.

This two-part paper proposes a revised method for calculating high voltage (HV) cable sheath currents, and for fault location of cross-bonded HV cable systems. The equivalent circuit and the cable impedance per unit length under short-circuit fault conditions are revised from those under non-fault conditions. Part 1 of this paper proposes a revised phasor domain mathematical model for the sheath current calculation under fault conditions, following demonstration that short-circuit faults can cause changes in the equivalent circuit of the cable metal sheath, and cause changes in the cable impedance per unit length. The calculation results, as given in a case study, show that there exists a unique relation between the fault position and the sheath fault currents, making it possible to locate a fault by analyzing the characteristics of the sheath currents during a fault. Part 2 of the paper focuses on the fault location method via sheath current monitoring.

Sheath current is one of the key indicators of underground power cable conditions. Considering the limitations of existing model-based methods for sheath current monitoring and difficulty in handling the increasing amount of unlabeled sheath current data accumulated by cable monitoring systems, we propose a data mining method based on unsupervised learning and spatiotemporal analysis of sheath currents for underground power cable monitoring. Tests based on real historical data demonstrate that the proposed method can effectively reveal unknown inherent patterns in unlabeled sheath current data.

Based on the Zhoushan alternating current (AC) 500kV cross-linked polyethylene (XLPE) submarine cable project, a method of metal sheath grounding via a low resistor, a low reactor, or a low resistor in parallel with a reactor at both terminals of the cable to reduce the power loss has been proposed in this paper. By numerically modeling the submarine cable system with the PSCAD/EMTDC software, the voltage and current distributions, and power loss on the sheath, armor and total submarine cable under three types of grounding impedors are calculated. The results show that with the increase of resistance value or inductance value, the sheath current decreases, and the armor current and sheath voltage increase, but the overall loss of the submarine cable decreases. When the submarine cable is operating under normal, short-circuit or transient conditions, in which the sheath voltage does not exceed the critical condition of these allowable values, the way that the sheath is grounded via a low resistor is the most beneficial to the power loss reduction. When the corresponding critical resistance value is 2.1 ohms at the start of cable and 1.3 ohms at the end respectively, it will reduce the power loss of cable for one phase 23.5% and the total power loss including resistors for one phase 14.2%, which is conducive to improving both the safety and operation economy of submarine cable.

In order to locate short circuit fault in power cable systems accurately and in a timely manner, this paper proposes a novel traveling-wave-based fault location method improved by unsupervised learning. There are two main steps of the method: a) record the traveling-wave data and build a sheath current matrix; b) cluster the data and identify the arrival time by the characteristic cluster. The improvement mainly lies in that the high-dimensional data can be directly used for clustering. A PSCAD (Power System Computer Aided Design) simulation has been carried out for a selected HV (high voltage) cable circuit. Results indicate that the hierarchical structure of condensed cluster tree just corresponds to the positional relationship between the fault point and monitoring points. The clustering results can be used for the identification of the arrival time of the traveling wave. The potential problems of the method lie in the “noise” identification. Ordinary samples can be labeled as “noise” by HDBSCAN. The combined use of DBSCAN and HDBSCAN maybe a solution for the “noise” problem.

The paper verifies that the advantages of sheath current over cable core current in fault detection, and designed a scheme to monitor the fault of Medium and Low Voltage cable in power system online which also can give an early warning when the insulation is damaged. The author built a 35kv cable model based on PSCAD, conducted simulation analysis on the low resistance earth fault, high resistance earth fault and sheath insulation fault of the cable, and further processed the analysis results with the wavelet analysis function in MATLAB, and finally established a mathematical model to analyze the error of the simulation data. It can be concluded that the current sheath method can not only effectively monitor the running condition of the cable online, but also give out the warning signal before the failure occurs. Meanwhile, the application of wavelet analysis also makes the data error smaller.

Due to recent advances, the numerical analysis of submarine three-core armored cables can nowadays be developed through the finite element method (FEM) in a small slice of the cable. This strongly reduces the computational burden and simulation time. However, the performance of this ultra-shortened 3D-FEM model is still to be fully assessed with experimental measurements. This paper focuses on this validation for an extensive variety of situations through the experimental measurements available in the specialized literature for up to 10 actual cables. In particular, it deals not only with relevant calculations at power frequency, like the series resistance and inductive reactance or the induced sheath current, but also with other aspects never analyzed before through 3D-FEM simulations, such as the zero sequence impedance, the magnetic field distribution around the power cable, as well as side effects due to the nonlinear properties of the armor wires. All this considering different armoring and sheath bonding configurations. Results show a very good agreement between measured and computed values, presenting the ultra-shortened 3D-FEM model as a suitable tool for the analysis and design of three-core armored cables, and opening the possibility to reduce the need of extensive experimental tests in the design stage of new cables.

In recent years, on-line monitoring and condition-based maintenance of HV cable systems have been extensively investigated to prevent cable fault. By analyzing cable sheath current, sheath defects can be identified. A new method of cable sheath defect identification is proposed in this study on the basis of the coding of the equivalent sheath impedance spectrum characteristics. In the proposed method, the sheath defects are identified by calculating the equivalent sheath impedance spectrum on the basis of the detected currents of the on-line sheath monitoring system. The equivalent circuit model of cross-bonded (CB) HV cable for sheath defect identification is constructed. The three-phase circuit model is decoupled to solve each phase independently in accordance with the CB scheme of the cable sheath. The equations of solving the equivalent sheath impedance are deduced. The criteria of sheath defect identification are proposed using the coding of characteristic parameters of the equivalent sheath impedance spectrum. Finally, a simulation model of the HV cable is built in the Simulink software to simulate 12 types of sheath defects. The simulation results have proven the correctness and efficiency of the proposed method.

A finite element code that solves self-consistent radio-frequency (RF) sheath–plasma interaction problems is improved by incorporating a generalized sheath boundary condition in the macroscopic solution scheme. This sheath boundary condition makes use of a complex sheath impedance including both the sheath capacitance and resistance, which enables evaluation of not only the RF voltage across the sheath but also the power dissipation in the sheath. The newly developed finite element procedure is applied to cases where the background magnetic field is perpendicular to the sheath surface in one- and two-dimensional domains filled by uniform low- and high-density plasmas. The numerical results are compared with those obtained by employing the previous capacitive sheath model at a typical frequency for ion cyclotron heating used in fusion experiments. It is shown that for sheaths on the order of 100 V in a high-density plasma, localized RF power deposition can reach a level which causes material damage. It is also shown that the sheath–plasma wave resonances predicted by the capacitive sheath model do not occur when parameters are such that the generalized sheath impedance model substantially modifies the capacitive character of the sheath. Possible explanations for the difference in the maximum RF sheath voltage depending on the plasma density are also discussed.

Cross-bonded three-phase single-core Cross-linked Polyethylene (XLPE) cables are widely used in power transmission and distribution systems. A great deal has been published on on-line monitoring of HV cable systems to prevent failure. Relative Dielectric Losses (DL) monitoring reveals the general condition of the cable insulation. Generally, DL measurement relies on measuring operating voltage and insulation leakage current. The main challenge to on-line monitoring of DL in Cross-bonded High voltage (CB HV) cables is the interconnectedness of metal sheath. Measured sheath currents are a combination of the leakage currents of each section and the imbalanced circulating current. Differentiating the leakage current of each interconnected section from the measured data is complex. The second challenge is that co-axial cables are used to connect cable sheaths to cable link boxes, for ease of installation and protection against moisture. As a result, any measured value contains currents from the two sheaths connecting at a joint. The third challenge is that it is hard to obtain the reference voltage synchronously and with high accuracy. Consequently, this paper investigates separation of leakage current components and analysis of DL based on leakage currents without reference voltage. A circuit model is proposed to describe the leakage current separation method for CB HV cables to allow on-line monitoring of DL, and the criterion required for assessing relative change of DL among different phases or sections of the cable for insulation deterioration are presented. Operational measurements from a cable system are analyzed and discussed. Results show that there is no significant deterioration in this monitored major section of a CB HV cable system.

The leakage currents detection is an effective method to evaluate the insulation condition of power cable. However, one of the significant challenges of the leakage currents detection is the leakage currents separation, because the leakage currents are mixed with the sheath circulating currents. Therefore, the leakage currents separation method of cross-bonded cable system based on sheath current vector difference was proposed and verified in the paper. Firstly, a separation method of differentiating the leakage currents and sheath circulating currents in the cross-bonded cable system with three imports of cross-bonded link box was proposed. Then, the simulation model of 110kV cross-linked polyethylene (XLPE)cable was established by PSCAD software. Furthermore, the separation method was used in cross-bonded cable simulation system. Finally, an actual on-site leakage currents testing of single-end-grounded cable system was carried. Simulation results indicated the proposed separation method can be accessible to differentiate the leakage current individually in the cross-bonded cable system with three imports of cross-bonded link box. The proposed simulation model can be applied to calculate the actual leakage currents in the single-end-grounded cable system.

Circulating current losses in sheath and armor of solid bonded single core medium voltage underground cable system are studied by means of analytical and numerical calculations. Analytical calculations are performed according to the standard IEC60287-1-1 and numerical simulations are conducted with finite element based computational software COMSOL Multiphysics. Dependency of these losses on cable laying configuration, cable structure and operational parameters are investigated by several case studies. First, COMSOL Multiphysics model is verified by comparing losses obtained by analytical calculations for a single circuit. Then the verified model is used to calculate sheath and armor loss for different configurations of two parallel circuits. Sheath and armor loss varies with different configurations of two parallel circuits and the configurations having the maximum and minimum loss are identified. Using the same models, effect of harmonics on sheath and armor circulating current loss is investigated.

Long-distance cables are often damaged by external forces due to site construction, resulting in protective layer grounding fault. Conventional fault location and detection methods, such as bridge method and traveling wave method, require on-site measurements along the cable, which results in heavy maintenance workload. For this reason, a method of online diagnosis and location of high-voltage cable based on sheath current is proposed. The simulation results show that when a fault occurs, the sheath current will change with the change of fault location and grounding resistance. Therefore, the external insulation faults of cables can be monitored, diagnosed and located on-line based on sheath current.

In this paper,an online cable fault location method based on Short-Time Matrix Pencil Method is proposed. In the 110kV cross-bonded cable hybrid line with GIS, the method does not need to disassemble the GIS of the cable terminal, and extracts the transient current traveling wave from the sheath ground wire of the cable ends. The Short-Time Matrix Pencil Method is used to extract the signal abrupt point in the current traveling wave caused by the short-circuit fault occurs in the line, and achieves the purpose of fault location. The cable system model is established in PSCAD to simulate different fault types and distances. Compared with the commonly used wavelet analysis method, the results show that the method has higher feasibility and accuracy.

WOS: 000443167700004, The sheath current causes cable faults and electroshock risk in high voltage underground cable lines. Also the sheath current increases cable temperature and it reduces cable ampacity. Hence, cable performance decreases due to the sheath current. Different precautions can be taken to reduce the sheath current effects in high voltage underground cable line. However, primarily the sheath current must be detected at the project phase of high voltage underground cable line. In literature, artificial neural networks are used for forecasting studies. In this study, artificial neural network (ANN) is used with particle swarm optimization, particle swarm optimization with inertia weight and genetic algorithm to generate hybrid ANN methods for forecasting of the sheath current. High voltage underground cable line is modeled in PSCAD/EMTDC to measure the sheath current of different high voltage underground lines, and the obtained data from PSCAD/EMTDC are used to train artificial neural network based hybrid methods to forecast the sheath current of any high voltage underground cable line. When particle swarm optimization with inertia weight is used with artificial neural network, hybrid ANN-iPSO method is developed. The results of ANN-iPSO are better than the results of ANN-GA and ANN-PSO. If ANN-iPSO is used to determine the sheath current, the sheath current of high voltage underground cable line can be determined at the project phase of high voltage underground cable line. Hence, the most suitable precautions can be implemented, and cable faults and electroshock risk can be prevented, also cable performance is increased in high voltage underground cable line.

The field analysis for a configuration of sheath helix in the presence of a coaxial metallic rod and strongly magnetized plasma under two conditions, i.e. , is presented. The electromagnetic field components in the configuration are obtained. The effects of a coaxial metallic rod in a plasma-loaded sheath helix traveling wave tube by means of a theoretical approach, in which infinite magnetic field has been adopted to represent the plasma response, is investigated. We presume that for the finite beam term, the mode structures remain unmodified and only the eigenfrequencies are modified. Therefore, the growth rate of slow electromagnetic waves and so their dispersion relation is calculated. Effects of frequency and plasma frequency on the growth rate are investigated. The obtained results are graphically presented.

Traditional analysis of cable early state recognition is mainly based on one or several threshold values of electrical characteristics, but the calculation of threshold is often affected by measurement accuracy and external disturbance, which inevitably reduces recognition accuracy. The development of artificial intelligence provides a new way to solve this problem. This paper presents a deep convolutional neural network (CNN) recognition method for early state of 10 kV single core cable based on sheath current. Firstly, waveform and energy characteristics which are extracted from the mutation information of sheath current by wavelet transform, are used to construct cable state recognition matrix. The mutational signal is detected by the cumulative sum (CU-SUM) method and intercepted by a set time window. Secondly, a 7-layer deep CNN is constructed according to the features of recognition matrix. Then the CNN model is trained by the adaptive moment estimation (Adam) method to get the recognition model of cable state. Finally, the proposed method is used to recognize cable early state by large number of samples which are obtained from the simulation of four cable states with PSCAD software. Compared with other methods, the results of simulation demonstrate that the proposed method has a high recognition accuracy.

The temperature of high-voltage cable has a great significance to reflect the operation status, and the accurate prediction of the joint temperature can improve the safe operating level of the wire. This paper points out a temperature prediction model based on least squares support vector machine (LS-SVM) to forecast short-term cable joint temperature. This paper also conducts a test on a Shanghai 110kV cable line with its joint’s history temperature, environmental temperature and humidity, the wire core/sheath current ratio data, and the particle swarm optimization algorithm (PSO) can be adapted to optimize model parameter standardization and regularization parameter dynamically. The results prove that method can predict the temperature of cable joint with high prediction accuracy and also provide a reliable basis for cable temperature detection and early warning system.

Using conventional methods, such as bridge method, traveling wave method, etc., it is unlikely to detect the fault location in a short time. A new monitoring and diagnosis method for high-voltage cables based on sheath current is proposed. The sheath current is measured to locate the cross-connected segment of the fault, leading to reduce the maintenance time. Considering the operation mode, cable parameters and line length, the sheath current equivalent circuit model of the cross-connected cable system was established according to the one-line laying type. Then a single-phase short-circuit fault in a cross-connected cable system was simulated. The results show that when the cable fault occurs, the difference of the sheath currents detected in the cross-connected sections are obvious. The grounding resistance, laying distance and cable length have less influence on the fault location. Therefore, based on the comparison among the sheath currents measured at the different minimum cross-section, the single-phase short-circuit fault can be accurately located.

Due to the current spreading of wind farms all over the world and their vulnerability to lightning strikes, it is important to investigate the lightning electromagnetic transients in wind farms. Underground cables are one of the essential parts in wind farms that link the turbines with the electrical grid. This paper investigates how the ground conductivity and relative permittivity, struck wind tower position, and rise time of lightning current influence the lightning electromagnetic fields impinging the underground cable sheath. The three-dimensional finite-difference time-domain method is implemented for this study. The lightning current through the cable sheath and its associated electric field can be effectively mitigated by connecting the grounding systems of the wind towers by underground bare wires called as counterpoise. Accordingly, the mitigation effect of counterpoise on the lightning current through the sheath and its associated electric field is also investigated. The results show that the lightning current through the cable sheath and its associated electric field is higher with lower ground conductivity. Moreover, it is revealed that the effect of both ground permittivity and struck wind tower position on the associated electric field and the sheath current is dependent on the ground conductivity.

통신 회선에 대한 전력선 전자유도 전압을 측정할 때, 일반 통신 케이블의 쉬스 층 및 측정 대상 통신 회선 접지의 상호 접속 관계에 따른 전압 변화를 비교 분석하였다. 케이블 양측 쉬스 접지 저항이 평균 $42.6{\Omega}$ 으로 유사한 상태에서 쉬스를 분리 접지하고 유도 전압을 측정하면 쉬스 접지를 하지 않은 상태에서 측정한 유도 전압에 대하여 10 % 미만 감소된다. 어느 한 쪽을 공통으로 접지하면 약 50 % 감소되고 양측을 모두 공통으로 하면 90 % 넘게 감소된다. 이것은 국제전기통신연합(ITU)에서 제공하는 계산식으로 계산하였을 때의 결과와 유사한 것으로 분석되었다. 아울러 ITU의 계산식을 활용하여 양측 쉬스 접지 저항 값을 변화시킬 때의 유도 전압 변화를 시뮬레이션하여 비교 분석한 결과, 실제 현장에서 쉬스 접지 저항 기준이 $100{\Omega}$ 이고 전화 국사의 저항이 보통 $10{\Omega}$ 이하인 점을 감안할 때 측정 오차율은 약 10 % 이하가 된다. 【The change in induced voltage according to the relationship of ground connection between the aluminum sheath layer and a conductor pair in a general telecommunication cable is analyzed. When a measurement is practiced under the condition of separated sheath grounds with an averaged ground resistance of $42.6{\Omega}$ , the induced voltage decreases 10 % to the induced voltage without sheath grounds. The induced voltage decreases approximately 50 % in the case of a one-sided common ground and decreases by more than 90 % in the case of a both-sided common ground. This experimental result is similar to the values calculated using the methods of the ITU Directives. In addition, according to a comparison analysis utilizing this ITU method, the measurement error range will be below 10 % in the state of ground resistance of central office less than $10{\Omega}$ and for the terminal side with $100{\Omega}$ less or more.】

This paper presents a method for detecting different types of defects in the cable sheaths interconnected in a cross bonding configuration of a HV cable system installed in flat or trefoil layout using the sheath currents as input data. Three different defects have been analyzed: electric continuity loss of earth connection, short-circuit between sectionalized metal sheaths of a cable joint and link-box flooding. The sheath current has been calculated by two different approaches, one on the basis of theoretical equations, programed in MATLAB® and the other on the basis of ATP software simulating the cable system model. The results obtained using both methods have achieved a good agreement between them. A simple criterion by the means of a easy normalized code of four discrete levels 0, 1, 2 and 3 has been developed to distinguish the magnitude level of change of sheath currents in case of the indicated defect existence in order to trigger alarm.

In order to improve the practice in operation and maintenance of high voltage (HV) cable circuit and localize short circuit fault accurately and in a timely manner, this paper proposes a fault localization method based on the monitoring of sheath current in cross-bonded HV cable circuits. The fault current flow can be identified by analyzing the fundamental component of sheath current, which can be obtained by Fast Fourier Transform (FFT) of the monitored sheath current. The cable section where a fault occurs can be localized as both ends of the cable section current would flow in opposite direction. The sheath current signals in different fault location within different sections have been simulated with a selected high voltage cable circuit and under typical operational mode. A set of fault localization criteria have been proposed. Results indicate that the proposed method is feasible and effective in localization of HV cable short circuit faults.

Length of most underground power cable in nation is not so long. Therefore it is operated without conductor transposition due to low unbalanced ratio. However, if cable length is long, line constant of each cable will be different. Different line constant can induce unbalanced voltage and current of sheath. Also it can induce several induced interference. This paper describes the operation effectiveness through steady and transient analysis on transposition and untransposition of cable conductor. Especially sheath current and induced voltage are analyzed and compared in case of transposition and untransposition. EMTP is used for modeling and analysis.

A self-consistent two-dimensional (2D) collisionless fluid model is developed to simulate the effects of the low-frequency (LF) power on a dual frequency (DF) capacitive sheath over an electrode with a cylindrical hole. In this paper, the time-averaged potential, electric field (E-field), ion density in the sheath, and ion energy distributions (IEDs) at the center of the cylindrical hole's bottom are calculated and compared for different LF powers. The results show that the LF power is crucial for determining the sheath structure. As the LF power decreases, the potential drop decreases, the sheath becomes thinner, and the plasma molding effect seems to be more significant. The existence of a radial E-field near the sidewalls of a hole may cause a significant portion of ions to strike the sidewall and lead to the phenomenon of notching.

The current and voltage in High Voltage DC (HVDC) line is not pure DC but contain superimposed ripple components. The current ripple in core of HVDC cable magnetically induces a voltage in the sheath, whereas the voltage ripple causes the flow of charging current from core to sheath. The knowledge of sheath voltage is necessary to ensure compliance with the specification of utility companies. In this work, we have reported that the models available in commercial Electromagnetic Transient (EMT) simulation software erroneously introduce a DC bias in steady-state sheath voltage and sheath current. We have also demonstrated that by removing the DC bias accurate steady-state evaluation of sheath voltage and sheath current is possible. Additionally, we have analyzed the sheath voltage and currents in HVDC cable considering different cable lengths and sheath grounding schemes. It has been found that grounding the sheath at the terminal of HVDC cable can limit the sheath voltage to acceptable levels without causing substantial joule loss in the sheath.

In this paper, we construct a numerical technique capable of solving Maxwell's equations in the frequency domain, both in vacuum and in cold magnetized plasma, with a boundary condition that guarantees the existence of a potential associated with the radio frequency electric fields tangential to certain surfaces. This potential is of interest to nonlinear sheath physics, since it enables the calculation of the time-dependent sheath current excited by a single-frequency electromagnetic wave and thereby the associated DC sheath current and sheath potential.In this paper, we construct a numerical technique capable of solving Maxwell's equations in the frequency domain, both in vacuum and in cold magnetized plasma, with a boundary condition that guarantees the existence of a potential associated with the radio frequency electric fields tangential to certain surfaces. This potential is of interest to nonlinear sheath physics, since it enables the calculation of the time-dependent sheath current excited by a single-frequency electromagnetic wave and thereby the associated DC sheath current and sheath potential.

In order to improve the practice in maintenance of power cables, this paper proposes a novel traveling-wave-based fault location method improved by unsupervised learning. The improvement mainly lies in the identification of the arrival time of the traveling wave. The proposed approach consists of four steps: (1) The traveling wave associated with the sheath currents of the cables are grouped in a matrix, (2) the use of dimensionality reduction by t-SNE (t-distributed Stochastic Neighbor Embedding) to reconstruct the matrix features in a low dimension, (3) application of the DBSCAN (density-based spatial clustering of applications with noise) clustering to cluster the sample points by the closeness of the sample distribution, (4) the arrival time of the traveling wave can be identified by searching for the maximum slope point of the non-noise cluster with the fewest samples. Simulations and calculations have been carried out for both HV (high voltage) and MV (medium voltage) cables. Results indicate that the arrival time of the traveling wave can be identified for both HV cables and MV cables with/without noise, and the method is suitable with few random time errors of the recorded data. A lab-based experiment was carried out to validate the proposed method and helped to prove the effectiveness of the clustering and the fault location.