Cable Sheath Research Articles

Research on the monitoring system for induced voltage and ground current of 27.5 kV cable sheath in railways

PurposeThe purpose of this study is to address the deficiency in safety monitoring technology for 27.5 kV high-voltage cables within the railway traction power supply by analyzing the grounding methods employed in high-speed railways and developing an effective monitoring solution.Design/methodology/approachThrough establishing a mathematical model of induced potential in the cable sheath and analyzing its influencing factors, the principle of grounding current monitoring is proposed. Furthermore, the accuracy of data collection and alarm function of the monitoring equipment were verified through laboratory simulation experiments. Finally, through practical application in the traction substation of the railway bureau on site, a large amount of data were collected to verify the stability and reliability of the monitoring system in actual environments.FindingsThe experimental results show that the designed monitoring system can effectively monitor the grounding current of high-voltage cables and respond promptly to changes in cable insulation status. The system performs excellently in terms of data collection accuracy, real-time performance and reliability of alarm functions. In addition, the on-site trial results further confirm the accuracy and reliability of the monitoring system in practical applications, providing strong technical support for the safe operation of high-speed railway traction power supply systems.Originality/valueThis study innovatively develops a 27.5kV high-voltage cable grounding current monitoring system, which provides a new technical means for evaluating the insulation status of cables by accurately measuring the grounding current. The design, experimental verification and application of this system in high-speed railway traction power supply systems have demonstrated significant academic value and practical significance, contributing innovative solutions to the field of railway power supply safety monitoring.

Comprehensive monitoring system for high voltage cables based on the ground current signal of the cable metal sheath

Abstract This paper has presented a comprehensive monitoring system for high voltage cables based on the ground current signal of the cable metal sheath. The system can collect and process the power frequency AC current and three high-frequency partial discharge signals in real time synchronously, which realize the synchronous detection of leakage current, relative dielectric loss, harmonic, partial discharge, and improve the integration of the hardware system.

Effects of Cable Sheath on Deformation Coordination between the Sensing Fiber and Sand

Effects of Cable Sheath on Deformation Coordination between the Sensing Fiber and Sand

Based on experiment and quantum chemical calculations: a study of the co-pyrolysis mechanism of polyesterimide enameled wires with polyvinyl chloride and the catalytic effect of endogenous metal Cu

Pyrolysis technology is a green and efficient method for recycling enameled wires. However, since waste enameled wires are typically recovered from electronic waste, they often contain small amounts of wires and cables. Therefore, during the pyrolysis process of waste enameled wires, it is inevitable for the paint film and the cable sheath to undergo co-pyrolysis. Polyesterimide enameled wires (EPEsI) and polyvinyl chloride (PVC) were chosen as represent enameled wires and cable sheath materials, respectively. Using thermogravimetric analysis with various pyrolysis kinetic analysis methods, the pyrolysis characteristics and kinetics of EPEsI and Mixture (mixture of EPEsI and PVC) were studied. Through synergy analysis and pyrolysis-gas chromatography/mass spectrometry analysis, the influence of PVC on the pyrolysis of EPEsI was elucidated from aspects such as pyrolysis characteristics and product distribution. Based on density functional theory calculations and wave function analysis, the role of endogenous metal Cu in EPEsI on the pyrolysis processes of PEsI and PVC, as well as the mechanism of HCl from PVC on the pyrolysis of PEsI, were clarified.

Numerical simulation of cable sheath damage detection based on torsional mode guided wave

In view of the cracking, sag, and damage of sheath caused by the load effect and external force impact of power cable, the echo parameters of cable sheath damage detection based on the characteristics of torsional guided wave propagation are studied in this work. According to the Navier displacement equilibrium equation, the dispersion curve of a magnetostrictive guided wave of the cable sheath was solved, and the T(0,1) mode with a group velocity of 1198.8 m/s and no dispersion was selected. Furthermore, while considering the excitation frequency, loss rate, and direction of the damaged section, the displacement field and the echo characteristic parameters of guided wave in the cable sheath were solved. Moreover, by analyzing the time-domain signals of damaged section echo, the cubic fitting function for the loss rate of the damaged section and the damaged section echo coefficient were obtained, which can effectively characterize the quantitative relationship between the damaged location, size, and guided wave echo of the cable sheath.

Climbing robot-assisted quantitative identification of sheath surface defects of stay cables

Sheath surface defect identification of stay cables using climbing robots or drones is gaining popularity. However, effective quantitative identification approaches remain challenging. This study proposes a cable climbing robot assisted quantitative identification method to address sheath surface defects combining the deep learning method and image processing techniques. First, standard and high-resolution cable sheath images, collected by an improved cable climbing robot with exclusive scales indicating the defect size, were categorised into three datasets according to defect types. Subsequently, a mask region-based conventional neural network (Mask R-CNN) model was developed for defect capture, with a connected domain algorithm quantifying defect areas. Perspective projection was applied to the defect masks to reduce the image distortion effect. The test results show that the model can achieve over 89% precision, recall and F 1-score for three defect types, with masks presenting overlapping rates reach up to 87% compared to the ground-truth regions. The quantitative identification results are promising to facilitate stay cable assessment and maintenance. Future study will be focused on extending the volume and categories of the dataset and improving the performance of the model.

Study on the burial depth calculation method for AC submarine cable based on the surface optical fiber monitoring temperature

AbstractThe partial exposure of submarine cable may cause damage to the metal sheath, which will affect its safe and stable operation. Existing detection methods for burial depth of submarine cables are difficult to implement and have a long detection period. In this contribution, a method is proposed to calculate the burial depth of alternating current (AC) submarine cable based on surface optical fiber monitoring temperature. According to the functional relationship between the transient temperature rise of submarine cable outer sheath above the ambient temperature and the burial depth (in the IEC‐60853 standard), the burial depth of submarine cables is calculated. The optical fiber temperature, electric load and meteorological temperature data are used for 30 consecutive days in September 2020 to calculate the change of burial depth of AC 500 kV oil‐filled submarine cable. The calculation results are basically consistent with the detection conclusion of side‐scan sonar, which shows that the method can accurately calculate the burial depth of submarine cables and locate the exposed position. This provides a theoretical basis for the intelligent operation and maintenance of AC submarine cables.

Important insights into steady-state calculations of voltages and currents in complex sheath bonding configurations of single-core cables

Ensuring effective sheath bonding holds paramount importance within underground single-core cable systems, as a misjudged selection can precipitate cable failures or jeopardize human safety. The foundation of a sound bonding design rests upon a meticulous examination of induced voltages and currents on the cable sheaths. To address this, guidelines and numerical techniques have been introduced, applicable to both handheld calculators and sophisticated software tools. However, their precision hinges on specific features and solving techniques, aspects that remain unclarified in current literature. This paper delves into a comprehensive exploration of sheath current and voltage calculations at steady-state in single-core cable systems. A rigorous benchmarking exercise is undertaken, comparing bonding-design simulation results derived from various computation methods. Moreover, the study scrutinizes the impact of several parameters, shedding light on crucial insights. Building upon this, the paper proposes modelling recommendations for the design and assessment of sheath bonding configurations in complex power cable installations.

Modified lignin-based intumescent flame Retardant's effect on flame retardancy, mechanical and electrical properties of HDPE material for cable sheathing

High-density polyethylene (HDPE) is a commonly used material for cable sheathing, which is a flammable material. To ensure the safe transportation of electrical energy, it is necessary to enhance the flame-retardant properties of HDPE materials. In this work, ammonium polyphosphate (APP) with lignin (Lig) is used as an intumescent flame retardant, and the flame retardant properties of APP/Lig for HDPE with different ratios are analyzed. It is found that with 3/1 ratio of APP and Lig under 30 wt%, the best flame-retardant performance is achieved. To further improve its properties, chemical modification of Lig with hexachlorocyclotriphosphazene (HCCP) is conducted to introduce nitrogen and phosphorus, obtaining NP-Lig. Flame retardant, mechanical and electrical properties are tested for the prepared material. The flame retardant tests show that the LOI of HDPE is increased from 23.8 to 28.2 by the addition of APP/NP-Lig, compared to that of APP/Lig. Mechanical tests show that replacing Lig with NP-Lig slightly increases the tensile strength and elongation at break of HDPE. Electrical tests show that APP/NP-Lig flame retardant maintains the electrical properties of HDPE under the industry standards.

Fault current calculation and grounding scattering optimization of 220 kV tunnel cable systems

Grounding faults in tunnel cables have received widespread attention. Establishing a fault model for tunnel cable systems in specific environments and proposing a fault current simulation method with high-speed computation and precise calculation accuracy is crucial for its stable operation. Additionally, optimizing grounding scattering method with better fault current scattering ability and conservation of land resources is of utmost importance. The metal sheath fault current of the tunnel cable is deduced using the double-sided elimination method. Based on the finite element method, three types of grounding scattering methods (i.e., spiral, cage and bearing platform) of working shafts are deduced. The ground surface potential of the working shaft is inferred with reference to human body safety limits. The result shows that the maximum cable sheath fault current reach 136.74 kA when the fault location is set at the beginning of the 1st major section. The cage grounding method effectively reduces the fault current density at the grounding point of the working shaft from 13,401.3A/m2 to 7192.8A/m2. When the number of vertical graphene conductors is increased to 6, the ground surface potential of the working shaft is 917.64 V, which is within the permissible range (955 V) for human body safety.

Co-pyrolysis mechanism of polyester enameled wire and PVC: A joint experimental and theoretical investigation

For the recovery of enameled wire, pyrolysis is a resource-friendly and effective process. However, because waste enameled wires are typically recovered from e-waste, a minor number of wires and cables are usually present. As a result, co-pyrolysis of the paint film and wire and cable sheaths is inevitable during the pyrolysis recovery of waste enameled wires. Polyethylene terephthalate (PET) polyester enameled wire and polyvinyl chloride (PVC) were chosen as representatives of enameled wire and cable sheath materials, respectively. The pyrolysis characteristics and pyrolysis kinetic parameters of enameled PET (EPET) wire paint, PVC, and Mixture (a mixture of the two materials, mEPET: mPVC = 9:1) were investigated using TG and various kinetic analysis methods. The combined pyrolysis index and Py-GC/MS were used to assess the co-pyrolysis of EPET and PVC and the products. The pyrolysis of EPET is adversely affected by the presence of PVC throughout the process; however, the presence of Cu in EPET may facilitate the HCl removal reaction of PVC. The co-pyrolysis products of EPET and PVC are more complex, and according to the different main functional groups, can be divided into monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons, phenols, ketones, aldehydes, alcohols, esters, carboxylic acids, chlorides, and others. Finally, density functional theory calculations were used to explore the co-pyrolysis mechanism of PET and PVC as well as the creation mechanism of various pyrolysis products. The catalytic mechanism of Cu contained in EPET on PET and PVC was explained from the perspective of electrostatic potential. This study provides a theoretical foundation and comprehensive reference for the pyrolysis and recycling of waste enameled wires.

Assessment method for 220 kv cable outer sheath damage based on bp neural network

220 kV high-voltage submarine cables find extensive application in offshore wind power transmission systems. Ensuring the safe operation of these cables involves accurately detecting and assessing the extent of damage to the cable sheath. This study begins by constructing a finite element simulation model for the cable based on its actual model. Subsequently, a method for evaluating the cable sheath’s damage state is proposed by using a BP neural network. The network takes ambient temperature, current, and six-point temperatures of the damaged section as input characteristics. Results indicate a correct rate of 94.29% for the BP neural network, demonstrating its effective discrimination of cable sheath damage levels. This approach introduces a novel evaluation method for cable sheath damage.

Effects of Die Entry Angle on the Mechanical Properties of Extruded Lead Alloy

The use of lead to produce wire, power cable sheathing, guide plates, and other wide-range applications require fine-grain structures. Researchers adopted severe plastic deformation, as a means of attaining ultra-fine grain structure. However, this technique is rather expensive and time-consuming. Thus, this study is focused on the application of a simple extrusion technique to achieve fine grain structure in the lead alloy by using different die entry angles to study the microstructural and mechanical properties of lead alloy. Lead alloy samples were cast into cylindrical billets in a sand mould, machined, and tapered at the edge to ease entry into the die for the extrusion process. The die tools were made of mild steel with die entry angles of 15°, 30°, 45°, 60°, 75°, and 90°. Subsequently, the extrusion was performed with the aid of a hydraulic press machine that provided pressure on a cylindrical punch and forced the billet through the extrusion die. The mechanical and microstructural properties were studied, using the micro-hardness tester and metallurgical microscope, respectively. The results show that the maximum extrusion stress of 70 MPa of lead alloy occurred at a die entry angle of 45°, which is three times that of the conventional alloy (18 MPa) with crystal clustering and fine microstructure. The ductility of lead alloy improved when processed at a 60° die entry angle with extrusion stress of 63.3 MPa, with no significant increase in hardness with die entry angles (7.7-9.0 HV). The grains show an appreciable reduction in size and enhanced surface finish

The mechanical strength of which in operation directly of the introduction into highly filled halogen-free plastics production

With the introduction into highly filled halogen-free plastics production, the mechanical strength of which in operation directly depends on the flame retardant content and application technology, it becomes important to control the cable sheath mechanical characteristics in a fireproof design. Polymeric materials and their compositions are viscoelastic materials for which the mechanical properties depend on the technological process of extrusion. The results of estimating the elongation at break of samples from the uniaxial stretching. It is shown that the inner and outer layers of the halogen-free plastic cable sheath have significantly different values of the plasticity normative parameter: differences evidence in the polymer structure in the inner and outer layers of the sheath due to the forced deformation process during extrusion, which is forced polymer structure orientation. It is shown that the inner and outer layers of the halogen-free plastic cable sheath have significantly different values of the relative change in specific mass of polymer samples. Analysis of the statistical covariance of the relative elongation at break and of the relative change in specific mass of polymer samples different in structure similar filled halogen-free polymers. With the introduction into highly filled halogen-free plastics application technology, it becomes important to control the cable sheath mechanical characteristics in fireproof design for the inner and outer layers

The Mitigation of Interference on Underground Power Lines Caused by the HVDC Electrode

High Voltage Direct Current power links are usually designed to adopt, on a continuous basis or during emergency operations, two grounding plants using the soil or seawater as a link–current return path. Such DCs flowing into the ground can cause problems, of which one of the most important is the increased risk of the corrosion of metallic structures in the area. Normally, the simplest mitigation technique is to keep an adequate distance between the main grounding plants and any metallic structure that can be corroded. Normally, such distances are not less than 5 km. However, there are situations where this approach cannot be applied, for example due to geographical constraints. In this paper, we describe and analyze the behavior of a mitigation technique that can be adopted when the HV pole cable is laid closer than the recommended distance to the main ground electrode. This paper is focused on the minimization of deleterious effects on the cable’s metallic sheath and its earthing points, distributed along it by means of sheath segmentation. The suggested approach appears well-suited to substantially diminishing the current flowing through the sheath of an HVDC power cable. In the segmented scenario, the sheath’s power dissipation is less than one-hundredth of that in the typical continuous configuration.

Steady-state electrical properties and loss reduction measures analysis for 220 kV tunnel cable system

This paper aims to reduce the tunnel cable systems’ power loss using different grounding and loss reduction methods. The submarine tunnel power cable project at Ningbo–Zhoushan in China is considered here as a case study. The cable is divided into micro-element segment, and their nodal admittance matrices are established using the telegraph equation. This approach helps to avert the prerequisite of diagonalizing the propagation matrix. For the analysis of induced voltage and circulating current in the cable sheath, the cascading algorithm is used while considering the presence of grounding node. It is found that the mixed cable laying methods and different lengths between minor sections result in a high circulating sheath current. This study finds that coordinating the amplitude and phase angle of series impedance inserted at the cross-bonded joint can reduce the cable system's power loss.

Moisture-driven degradation mechanisms in the viscoelastic properties of TPU-Based syntactic foams

Syntactic foams have found widespread usage in various applications including, marine, aerospace, automotive, pipe insulation, electrical cable sheathing, and shoe insoles. However, syntactic foams are often exposed to moisture when used in these applications that potentially alter their viscoelastic properties, which influences their long-term durability. Despite their significance, previous research has mainly focused on experimental studies concerning mechanical property changes resulting from filler loading and different matrix materials, overlooking the fundamental mechanisms resulting from moisture exposure. The current paper aims to bridge this gap in knowledge by elucidating the impact of long-term moisture exposure on TPU and TPU-based syntactic foam through multi-scale materials characterization approaches. Here, we choose a flexible syntactic foam manufactured using thermoplastic polyurethane elastomer (TPU) reinforced with glass microballoons (GMB) through selective laser sintering. Specifically, the research investigates the influence of moisture exposure time and the volume fraction of GMB on chemical and microphase morphological changes, along with their associated mechanisms. The study further examines how these microphase morphological changes manifest in viscoelastic properties.

Detection of water leakage defects in cable insulation sheath based on terahertz time-domain spectroscopy

Water leakage of the insulation sheath can lead to a decrease in the insulation performance of the power cable, which poses a hidden danger to the power cable. Accurate detection and positioning of the water leakage area are crucial for improving power safety and stability. In response to the water leakage defect of the cable insulation sheath, this article proposes a method based on reflective terahertz time-of-flight tomography technology to measure the water leakage area of the insulation sheath. A sample of insulation sheath water leakage defect was prepared by simulating real scenarios. By analysing the terahertz reflection time-domain optical spectrum and imaging results of the sample, the location and area of the insulation sheath water leakage defect can be accurately measured, verifying the application potential of reflective terahertz time-of-flight tomography technology in detecting water seepage defects in cable insulation sheaths.

An Experimental Study for Deriving Fire Risk Evaluation Factors for Cables in Utility Tunnels

In this study, we performed three tests to measure the fire-retardant performance of power cables installed in utility tunnels. The standards we applied for testing are ISO 5660-1, NES 713, and IEEE 1202. Specifically, we performed a cone calorimetric analysis, calculated the toxicity index, and measured the flame spread length on material surfaces. Even though the same fire-retardant chemical composites were applied, various differences in fire-retardant performance were found depending on the chemical properties of the cable sheath and insulation. We also found that gaseous substances generated during the burning of cables can serve as important risk assessment factors in fires. We determined that, in addition to the heat generated when the cable burns, the toxic gases emitted at this time can also be a risk factor. This is because it is important to consider any potential risk to a person entering as part of an initial response to an event or accident involving cables installed in utility tunnels. Moreover, in the event of a fire in the cable, there is a risk of hazardous substances flowing into the city center as toxic gases are released. Therefore, we determined that the risk of hazardous gases emitted during cable fire should be reflected in the fire-retardant performance standard.

Facile Synthesis of Melamine/G-C3N4 Covalent Organic Framework (COF) by Indirect Intercalation and Its Flame Retardant

In this paper, a covalent organic framework (COF) based on g-C3N4 was designed firstly. The COF is arranged through an indirect interrelation method among melamine and g-C3N4. During the reaction, Cu2+ was used to expand the layer space of g-C3N4. The as-prepared COF were characterized by SEM, TEM, FTIR, and XRD. The obtained product is a melamine interrelation g-C3N4 composite material (MCN) with COF structure. The MCN was used as flame retardant for cable sheath material. The thermal stability, thermal shrinkage, oxygen record and vertical burning of link sheath material contain MCN were tested. The results showed that the MCN flame retardant increases the thermal stability time of the sheath material from 89 min to 131 min, and the thermal shrinkage rate diminished from 4.17% to 2.00%. The LOI is 29.5, and the flame retardant grade reaches UL-94 V-0. The SEM analysis of the carbon residue of the cable sheath material after burning, it was found that the state of the carbon layer of the link sheath material transform into a thick honeycomb structure by the impact of the MCN flame retardant, which forestalls the dispersion of oxygen and burnable gases, in this way hindering the transmission of flame.