Cable Sheath Research Articles

A precise analytical method for fault location in HVAC cables

The protection of high voltage alternative current (HVAC) cables is of paramount importance, because conventional distance relays are not capable to precisely determine the fault location. The mutual inductances between core and sheath in HVAC cables as well as significant capacitive effects exert undesirable impact on the seen impedance by distance relays. Thus, in this paper, a new analytical method is proposed for fault location in HVAC cables employing measured voltages and currents at both ends. In the proposed method, the cable is modeled adopting the distributed form of the main parameters. The proposed fault locator searches the entire length of the cable to determine the location of core-to-sheath faults as well as the corresponding fault resistance. To implement the algorithm established in this study, a HVAC underground three-phase single-core cable is simulated in PSCAD/EMTDC environment. Comprehensive simulation studies are conducted by considering different bonding methods, fault resistances and fault locations. Moreover, the performance of the proposed fault locator is evaluated in different operating conditions including noisy environments, source impedance changes, different load levels, high fault resistance, and uncertainties in cable parameters. The results demonstrate that the estimation error does not exceed 1%, which is desirable for practical applications.

Losses Computation in Thin Conductive Sheaths of Power Cables via an Integral Approach

A thin-shell integral equation formulation is applied to the computation of eddy-current losses in submarine ac cables. The continuous helical symmetry of the geometry is exploited for reducing the computational cost of the simulation.

Transient Thermal Performance of Power Cable Ascertained Using Finite Element Analysis

This paper presents the computation of the cable ampacity and the temperature distribution through long duration based on the equivalent thermal circuit based on IEC 60287 standard and the Finite element method using COMSOL (Multiphysics environment, version 5.5). This study investigated the cable ampacity and the temperature rise of the cable core and sheath at steady state and emergency conditions. The cable ampacity was investigated at different conditions such as the variation of cable depth, soil properties, and soil temperature. The results confirmed the adaptation between the thermal circuit results and the COMSOL results as well as the effectiveness of using the numerical method to compute the cable ampacity. Using the COMSOL-based thermal properties evaluations, the transient performance of the cable is ascertained. The transient study is performed for different cable loading currents and dry zone sizes.

An accurate analysis of lightning overvoltages in mixed overhead-cable lines

An accurate investigation of lightning overvoltages on a typical mixed overhead-cable line is performed. The recently developed extended transmission line (TL) approach, frequency-dependent (FD) soil model and FD grounding system modeling method are also reviewed. The wave propagation characteristics of an overhead and a cable in frequency domain are studied using classical and extended TL approaches. Moreover, transient simulations using Numerical Laplace Transform (NLT) are carried out with different FD soil parameters and FD grounding behavior, and the influences of FD characteristics on the transient cable sheath voltages are made clear.

VHF/UHF Miniaturized Ferrite-EBG Composited Choke Structures

Parasitic currents on the sheaths of the coaxial cables will deteriorate the performance of the antenna, so the choke structures are needed. While a-quarter-wavelength choke sheaths at VHF and UHF are very long, miniaturized ferrite-EBG composited choke structures are proposed. The ferrite refers to ferrite magnetic beads. Electromagnetic bandgap (EBG) element is consisted of multi-section metal tubes with length relatively shorter than a-quarter-wavelength. The integrated structures are formed by arranging EBG elements and beads alternately along the coaxial line. The proposed choke structures combine the wideband choke performance of the ferrite beads and the high efficiency of the EBG structures. Furthermore, due to the difficulty of the quantitative measurement of the choke structures in an open space, a measuring setup designed in a transmission line model is devised. The choking effects of the proposed structures can be characterized by the |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> | parameter of the measuring device, as the direction of the currents flowing on the sheaths of feeding cables are the same as that of the currents on the inner conductor of the measuring device. Meanwhile, choking bandwidth, efficiency and size of the ferrite-EBG composited choke structures are compared with that of EBG structures and beads. The influence of different numbers of the proposed structures is studied. A prototype is fabricated and measured. The overall size of the ferrite-EBG composited choke structures is 0.25 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×0.024 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×0.024 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> (415 mm ×40 mm ×40 mm) ( λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is the wavelength of the lower end of the operating frequency band). The measured choking band ( |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> | <; -10 dB) is in the region of 181-343 MHz.

Research on hot air ice melt system for cable sheaths of Er’qi Yangtze River Bridge

To prevent the cable sheaths of Er’qi Yangtze River Bridge from freezing under bad weather in winter, which may lead to ice fall and bring traffic safety accidents, a theoretical model and technical scheme of hot air ice melt system for Er’qi Yangtze River Bridge has been proposed. Based on the established heat transfer model for cable sheaths, the characteristics of heat transfer between internal hot air and outdoor environment have been analyzed. Under the condition when the temperature of the end of cable sheath’s outwall is more than 3°C, the range of temperature and speed of input hot air were estimated, which provides a theoretical basis for hot air melt system for cable-stayed bridge sheaths.

The estimation of ship cable condition by the means of measuring its insulation characteristics

Timely detection of defects in electrical equipment and cable network is required for the ensuring the fire safety of a modern marine vessel. The method of continuous monitoring of the resistance value of cable insulation is not very informative and is not applicable for assessing the service life of cables and predicting their replacement during operation and repair. Currently the problem of developing modern non-destructive methods of insulation control is very urgent in order to determine the operability of the cable, search for diagnostic parameters characterizing the state of insulation during prolonged aging, as well as the introduction of traditional methods of diagnostics of electrical equipment that have shown their effectiveness at the facilities of the coastal infrastructure. A promising solution for this problem is a method for monitoring the values of the tangent of the dielectric loss angle tgδ of cable insulation using devices that allow registering parameters with high accuracy. In this study the determination of changes in the parameters of a ship cable subjected to accelerated thermal aging at temperatures 120-130 °C has been made. The tgδ measurements of the cable sheath have been carried out using the Tangent-2000 insulation meter. The tests have shown that aging of cable hose insulation is accompanied by a non-linear change in tgδ; at certain values of the tangent of dielectric loss angle, visible cracks appear indicating the onset of an emergency condition of the cable. The nature of the change in the parameter tgδ is explained by the occurrence of reactions of oxidative dehydrochlorination of polychloroprene in the process of thermal aging of insulation and changes in its mass. Thus, the tangent of the dielectric loss angle can be one of the diagnostic parameters for assessing the state of the insulation of the ship's cable and predicting its service life.

Tape winding angle influence on subsea cable sheathing fatigue performance

A fundamental component of subsea power cables is the thin galvanized steel tape winded around the dielectric and sheathing layer in order to prevent permanent thermal cycling induced deformation. The pressure state induced by the resistance offered by such tapes against radial reformation reduces the triaxiality ratio of the stress state of the lead sheathing layer. It is known that a reduced triaxiality has a beneficial effect on ductility and fatigue life of metals. In the present work a series of finite element simulations are performed in presence of galvanized steel tapes at three different winding angles and without such reinforcement at all, obtaining a qualitative indication of its effect on the stress state induced in the sheathing layer. Loading conditions as internal pressure related to thermal dielectric expansion and cable bending are modelled. The numerical qualitative results are discussed in connection to a series of full-scale fatigue tests performed on subsea power cables with and without the support of steel tapes.

СИСТЕМА ДИСТАНЦІЙНОГО МОНІТОРИНГУ СТАНУ ВИСОКОВОЛЬТНОЇ КАБЕЛЬНОЇ ЛІНІЇ

The article proposes a device for remote monitoring of high-voltage cable line state. The device gives a possibility to measure simultaneously several diagnostic characteristics, i.e. the temperature of cable outer sheath, electric current in cable core, capacitive current to earth and uses a specially designed internal electric power source that directly converts the energy of cable electromagnetic field into electric energy with necessary parameters. By computer simulation, the temperature field distribution in the cable cores of 330 kV cable line is determined and the quantitative relationship between the directly measured temperature on the cable outer sheath and the temperature values of the cable core and insulation, which are important diagnostic characteristics of the thermal state of power cables is revealed. References 5, figures 3.

The urban lead burden in humans, animals and plants

Urban residence is a risk factor for children’s elevated lead exposures. Evidence from domesticated and wild animals shows that the phenomenon crosses species lines. Plants also suffer under lead’s phytotoxicity. The Industrial Revolution lured and drove more than half of the US populations from the countryside into cities. Leaded paint, lead in public water systems and later, leaded gasoline, were the principal contributors to lead contamination of US cities. Lead’s incredible utility has resulted in thousands of commercial applications in electronics, hardware, paints and pigments, many types of glass, ceramic glazes and coatings, cable sheaths, machinery and manufacturing, light industry, radiation protection, post and telecommunications, metallurgy, chemical production, transportation (rail, automobile and aviation), construction, weapons, aerospace, oil, plastics and petrochemicals, plumbing, pesticides, hair products, etc. Historically, commercial and industrial activities occurred coterminously to habitation, so the beginnings of all these uses occurred within urban areas. Consequently, urban areas have high lead pollution levels. Lead toxicosis in urban areas is evident across animal species, including pets (Zook et al 1998, Langlois et al 2017), feral pigeons (Cai and Calisi 2016), wild raccoons (Hamir et al 1995) and foxes (Dip et al 2000) and gazing animals (Ward and Savage 1994), Indeed, in 1970, pigeons were considered a sentinel for urban lead pollution (Tansy and Roth); society has continued to use children. Plants in urban areas are also significantly affected by high lead levels (EPA 1984). We used an integrated One Health approach to assess lead’s urban burden in humans, animals and plants. In the future, we will develop conceptual and pragmatic guidance for urban planners and decision makers to address the urban lead burden in humans, animals and plants.

On the aerodynamic characteristics of inclined stay cable sheaths in the critical flow regime

This paper studies the presence of the bistable flow activity around inclined cable models. It presents results from wind tunnel test on static original High-Density Polyethylene cable covers in a range of Reynolds numbers from the subcritical to the critical regime, inclined at angles of 90°(vertical), 60°and 45°. It has already been shown that, in the critical regime, turbulent transition in the boundary layers around a circular cylinder exhibits bistable behavior at zero inclination, i.e. the boundary layer on either side is intermittently turbulent or laminar, leading to intermittent asymmetry of the flow and resulting aerodynamic loads. The present wind tunnel tests consist in measuring the pressure patterns around inclined circular cylinders using numerous pressure taps. Bifurcation diagrams are created in order to quantify the occurrence of bistability and Proper Orthogonal Decomposition is used to identify the geometrical flow modes that are governed by the bistability. The results show that the bistable phenomenon is only identified in the Reynolds number range corresponding to the first transition between the TrBL0 and TrBL1 regimes. Furthermore, the inclination angle seems to have a significant impact on the energy of the flow mode related to unsteady asymmetric reattachment. This paper also treats the potential sensitivity of the aerodynamic drag and lift forces to the circularity defect of the covers and presents the positive impact of the helical fillet on controlling the bistable activity at a critical inclination angle of 60°.

A Model for Assessing the Magnitude and Distribution of Sheath Currents in Medium and High-Voltage Cable Lines

In this article, the authors discuss a simulation model to study the effect of cross-bonding of metallic sheaths, and/or nonmagnetic armors, of single-core medium- and high-voltage cables in the same circuit. In single-core cables, the resistive losses due to the induced circulating currents in cable sheaths or armors cause an increase of the cable temperature, which therefore reduces its ampacity. This is a serious issue affecting the distribution and transmission lines. In addition, the risk of electric shock due to induced voltages may be present if a person is in contact with the armor/sheath at its unbounded end. For these reasons, special bonding techniques of metal sheaths are employed to reduce these currents. The simulation model to assess the magnitude and distribution of induced armor/sheath currents of medium- and high-voltage cables that is herein proposed may be used to optimize the cross-bonding configuration of single-core cables employed in high-current industrial applications or in transmission/distribution power grids. The model has been experimentally validated by means of actual data from a high-voltage underground line and field measurements performed by Prysmian Electronics.

Investigation of Novel DC Wind Farm Layout During Continuous Operation and Lightning Strikes

This paper proposes a novel layout for a grid-connected DC wind farm (DCWF) and investigates the performance under continuous operation and direct lightning strikes particularly for high soil resistivity. The DCWF employs internal dc grid that supplies generated power to the host AC utility through high voltage direct current (HVDC) transmission link. The proposed layout ensures sustainability of power supply against potential interruptions of DCWFs either during normal conditions or lightning incidents to comply with grid codes regulations. During continuous operation, the proposed layout safeguards the entire DCWF cables against flow of return currents to avert derating of conductor ampacity. Besides, protects WT nacelle switchgear and entire interface converters against hazards of surge currents. Furthermore, an effective grounding system design is proposed to introduce a low impedance path for system return currents, minimize voltage drop across grounding impedance and thus maximize DCWF delivered power to the grid. A detailed system that sufficiently represents models of system cables, grounding network and interface converters is built to verify the proposed scheme significance. The obtained results assure the capability of proposed layout to cease return currents via cable sheath during continuous operation and provide superior mitigation of lightning-associated transient voltages and currents.

An investigation of harmonic induced voltages on medium-voltage cable sheaths and nearby pipelines

This paper investigates the impact of harmonics in underground medium-voltage cables to the induced voltages on the cable sheaths of the excited system as well as the corresponding electromagnetic interference (EMI) to nearby coated pipelines. To evaluate systematically the harmonic induced voltages on both cable sheaths and pipelines a benchmarking analysis is carried out. The accuracy of different simulation models is also investigated. The feasibility and practical application of this paper is examined in a cable system excited by current harmonics using data obtained from measurements of the recent literature.

Evaluation of cable moisture-proof measures based on AHP

With the widespread use of cross-linked polyethylene (XLPE) cables in the power system, the problem of aging due to moisture ingress of XLPE cables is becoming increasingly prominent. Under the humid laying environment, the XLPE cable sheath is easy to damage. The storage seal is improper or the water fill in the cable channel causes the XLPE cable to be immersed for a long time, which will seriously affect the insulation and service life of the cable. Therefore, it is important to establish a systematic evaluation system for moisture-proof measures of XLPE cables. This paper analyzes the reasons for the moisture of XLPE cables and the common moisture-proof measures. Based on the AHP method, comprehensively considers the impact of economy, technicality, applicability and feasibility, and establishes an evaluation system of cable moisture-proof measures. In the evaluation system, the criteria layer is subdivided into seven secondary indicators. For the plan layer, comprehensively consider the XLPE cable structure, cable materials, cable accessories and laying environment and other factors to select the XLPE cable moisture-proof measures for comparison. This paper uses AHP to figure out the comprehensive weight of each moisture-proof measure to the target layer, and the consistency test was conducted to prove the validity. The results have shown that the XLPE cable using water treeing resistant material in the plan layer has the best comprehensive effect. This paper provides a systematic and comprehensive evaluation system for future researches on cable moisture-proof measures, and the research results provide reference value for cable design and selection in the hot and humid areas.

Sheath induced voltage prediction of high voltage cable based on artificial neural network

This paper aims to propose an Artificial Neural Network (ANN) model for voltage prediction in cable sheath of combined overhead-cable line under lightning condition. To this end, the effect of different parameters, including tower footing resistance, sheath ground resistance, a kind of ground connection of sheath on the maximum induced voltage of cable sheath in 132 kV combined line are investigated using EMTP/RV software. It is assumed, in this study, that lightning strike to the Guard wire and back-flashover occurred and/or lightning strike to the overhead line. With these results in mind, the proposed model is designed with ten inputs data and four outputs data. The validation of the model indicates that the absolute values of relative errors between induced voltages of simulation and prediction are less than 8%. This indicates high efficiency of ANN technique in the maximum induced voltage prediction of cable sheath under lightning surge.

Effects of magnetic field on cable sheath corrosion

This article presents the results of research on the effects of utility-frequency magnetic fields on aluminum sheath corrosion of three-phase power cables in a 3 wt% NaCl aqueous solution. Various conditions were considered, including rotating and pulsating magnetic field and connection of the cable to a high-voltage source to research the degradation of aluminum sheath under conditions close to real operation. Influence on surface morphology was evaluated through scanning electron microscopy, energy-dispersive spectroscopy, and X-ray crystallography. Chemical analysis of NaCl solution samples was used to determine how aluminum concentration changes over time, demonstrating the effects of magnetic field. Influence of magnetic field on the evolution of field-gradient force near the sheath was also researched.

Y-Parameters Model of Cross-Bonded Cables Including Bonding Wire Impedances

Cables with cross-bonded cable sheaths are predominantly used in high-voltage ac systems. Existing frequency-domain models of such cables use ABCD-parameters, which may cause numerical problems in the high-frequency region, or Y-parameters. The existing Y-parameters model excludes bonding wire impedances which may result in inaccurate estimates of the magnitude or frequency of the cable input impedance at resonant frequencies. This letter extends the formulation of an existing Y-parameters model to include bonding wire impedances. The proposed extended formulation is validated against a cable model in commercially available EMT-type software, in frequency- and time domain. For a certain bonding wire impedance model, the proposed Y-parameters model is shown to have a lower magnitude of the cable input impedance at resonant frequencies compared with a model excluding bonding wire and grounding impedances.

Measuring Cable Sheath Currents to Detect Defects in Cable Sheath Connections

Measuring Cable Sheath Currents to Detect Defects in Cable Sheath Connections

Investigation into the toxicity of combustion products for CR/EPR cables based on aging period

The toxicity of combustion product gas of CR/EPR cables, which are widely used in nuclear power plants, has been investigated according to the aging period. The cable specimens were prepared by thermal acceleration aging method, from non-aged to 40-year-old cables at spans of 10 years. The cable sheath and insulation materials were tested separately. The test was conducted in accordance with the Naval Engineering Standard 713 standard code, which measures the amount of 13 exhaust toxic gases when 1 gram of the test specimen is burnt. The toxicity index and the amount of emission gases were varied irregularly with respect to the aging period, and the reason for this result could not be clearly explained due to the lack of information on cable material. However, the reason could be qualitatively estimated to have two conflicting effects: (1) Reduced flame retardant performance as the devolatilization process proceeded over time, and (2) the enhanced stabilization of double bonds between carbon compounds and flame retardant elements, such as chlorine or bromine, as the cable is aged. The toxicity of the accelerated aging period of 20 years was much higher than that of non-aged cables, which signifies increased probability of fire risks of aged cables from the viewpoint of toxicity. Furthermore, when comparing the adjusted toxicity index calculated without CO, CO2, and NOx emission, it can be clearly determined that the average toxicity index of aged cables is higher than that of non-aged cables. Thus, in conclusion, human hazardousness of a cable fire increases from the viewpoint of toxicity of emission gases as it deteriorates, so safety regulations or maintenance guides for old nuclear power plants should be reinforced considering this toxicity variation. The results obtained from this study can be used to improve the reliability of operator manual actions for safety-shutdown and fire-suppression activities and to provide basic information for studies on fire suppression.