Cable Surface Research Articles

Influence and comprehensive evaluation of porous metal foam filled fins on the performance of power cable surface waste heat recovery thermoelectric power generation device

Cables are essential components in power systems. Certain amount of heat is generated during the energy transfer process. Effective recovery and utilization of waste heat generated by cables is a helpful proposition. In this study, a cable waste heat recovery thermoelectric generation device (CTEG) is proposed. By installing cooling fins and thermoelectric generation devices on the cable surface, the waste heat on the cable surface is converted into electric energy. To improve the power generation efficiency of the device, a method of filling porous metal foam material in the fin teeth gap is used. The results demonstrate that filling the fin teeth gap with porous metal foam material with high porosity and low pore density (PPI) can significantly increase heat transfer efficiency and benefit the output power of the thermoelectric generation device. The flow field in the pipeline of thermoelectric generation device is also analyzed in this study. A comprehensive evaluation method is proposed to consider the power generation efficiency and heat transfer efficiency of the thermoelectric generation device. It is shown that filling porous metal foam material with high porosity and low pore density can maximize the power generation efficiency of the thermoelectric generation device, and at the same time, the pipe pressure drop loss can be compensated by the improvement of heat transfer. This research is significant because it provides useful information for enhancing the energy conversion efficiency of thermoelectric generation devices that recover waste heat from cable surfaces and generate electrical power.

Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables.

Effects of Installing Different Types of Cooling Fins on the Cold Side of a Thermoelectric Power Generation Device on the Thermal Efficiency and Exergy Efficiency of Power Cable Surface Waste Heat Recovery.

This study investigates the thermal efficiency and exergy efficiency of a thermoelectric power generation device for recovering power cable surface waste heat. Numerical simulations are conducted to analyze the impact of different types of cooling fins on the system's performance. The results demonstrate that the installation of cooling fins improves heat transfer efficiency and enhances the thermoelectric power generation device's output power. Among the various fin designs, the system equipped with cooling fins with 17 teeth exhibits the highest performance. These findings highlight the importance of fin design in optimizing the system's thermal efficiency and exergy efficiency. This study provides valuable insights for the development and improvement of thermoelectric power generation systems for power cable surface waste heat recovery applications.

Effect of the upper rivulet on the aerodynamic forces and vibration of stay cables in the critical Reynolds number range

During the rain-wind-induced vibration (RWIV) process, a water rivulet forms on the surface of stay cables, and the upper rivulet is considered to be an important factor in RWIV formation. The cables also exhibit galloping in the absence of rain. To reveal the effect of a rivulet on galloping and help explain the mechanism of RWIV, from the viewpoint of the Reynolds number effect, a cylinder with an artificial rivulet at multiple angles was tested in wind tunnel experiments. The results show that the rivulet has a significant effect on the aerodynamic force coefficients, and the increase in the rivulet position decreases the onset Reynolds number of TrBL0-1 transition. A large-angle rivulet limits reattachment on the upper surface of the model, and the vortex appears in TrBL1. Due to reattachment, bistability can be observed in the TrBL0-1 and TrBL1-2 transitions, and the wake vortex is suppressed. During the formation of a separation bubble, the aerodynamic forces change dramatically, which affects the aerodynamic damping of the cables and induces galloping instability in most cases. The condition of reattachment on the upper surface of cables may be an important reason for RWIV occurrences.

The Pretension Design of Cable Mesh considering the Large Deformation of Ring Truss

The conventional pretension design of cable mesh usually takes the ring truss as a rigid body or assumes small deformation. This method needs to be more accurate in designing super large aperture antennas. A cable mesh design method considering the large deformation of the ring truss is proposed in this paper based on the flexible multibody dynamics (FMD) and the force density method (FDM). With this method, the significant range deviation of the boundary points’ position of the ring truss under the tension of the external area of the cable mesh after the completion of the pretension design can be predicted with high accuracy. After the ring truss and cable mesh surface are assembled stably, there is only a minimal deviation between the actual mesh surface and the theoretical mesh surface of the antenna, and there is only a minimal deviation between the genuine mesh pretension and the design pretension. The above calculation method is verified by numerical simulation, and the simulation results show that the technique can be applied to the mesh pretension design of a super large aperture ring deployable antenna.

Effects of damping and helical fillets on galloping vibration of stay cable installed with a rectangular lamp

Lamps attached on the stay cable can change the stable circular cross-section of the stay cable, which is easy to cause galloping vibration. Stay cables of the Kuipu bridge in the Fuzhou City of China were equipped with damper and helical fillets. After the installation of rectangular lamps on this bridge, no obvious vibration of the stay cables was observed. This is totally different from another bridge, the Kuimen bridge in the Chongqing City of China, which has been recently reported by the authors. The purpose of this study is to clarify the effects of the helical fillets and the structural damping on galloping vibration. The features of galloping vibration of the stay cable attached to a rectangular lamp were carefully studied, and the effectiveness of damping and helical fillets in reducing the galloping vibration was evaluated. First, the force measurement wind tunnel tests on the segmental test model were carried out, and the lift and drag coefficients of the stay cable attached to the rectangular lamp were measured. The dangerous wind attack angle of galloping vibration was predicted by the galloping force coefficient. Second, 3-dimensional vibration measurement wind tunnel tests were carried out to measure the wind-induced response of the cable-lamp test models. The variation of wind-induced response of stay cable with yaw angle and wind velocity was measured for test models with and without helical fillets. In the test, the features of wind-induced vibration were studied at the damping level of 0.1%, 0.6%, 0.7%, 0.8%, and 1.0%. According to Den Hartog’s theory, the minimum coefficient of galloping force is about −9.8. The experimental results of 3-dimensional vibration measurement wind tunnel tests show that the helical fillets wrapped on the cable surface can enhance the critical wind velocity to a certain extent, but the critical wind velocity is still far lower than the design wind velocity. When the damping ratio of the stay cable is up to 1.0% ( SC = 35.1), the galloping vibration of the stay cable attached to a rectangular lamp on the Kuipu Bridge can be effectively mitigated.

Temperature mapping model of cables considering the coupling of electromagnetic and thermal field

Background: During cable operation, its internal temperature reflects the actual working condition of the cable. Once overload occurs, its conductor temperature will rise rapidly. Under high temperature conditions, the insulation material is very prone to breakdown accidents, which seriously threatens the safety of the power system. Methods: To reflect the actual operating condition of cables with high fidelity, a cable temperature mapping model is proposed with the coupling of electromagnetic and thermal field taken into consideration. Firstly, a finite element model is formulated based on the cable structure and material parameters. Secondly, the coupling between electromagnetic and thermal field is analyzed, and multiple coupling calculations are performed iteratively according to the operating conditions. Finally, the mapping between temperature and current flowing through the cable is established to accurately reflect the variation of cable’s internal temperature under different operating conditions. The cable surface temperatures under five operating conditions are measured online and compared with the calculated results of the temperature mapping model. Results: The absolute error between the calculated value of the model and the actual measured value is 0.88°C and the relative error is 1.46%. Conclusions: The temperature mapping model developed in this paper can accurately calculate the internal temperature of the cable and forms an important part of the digital twin model of the cable.

A many-body dissipative particle dynamics study of droplets impacting on fiber

Collisions between droplets and fibers are a common phenomenon in nature and daily life, such as raindrops on the surface of spider webs and the surface of transmission cables. We present a numerical model to study the droplets impacting on fibers with the many-body dissipative particle dynamics (MDPD) method. The droplets impact on neutral fiber at different velocities and diameters is simulated. The diffusion trend of droplets is affected by the velocities and diameters. According to the morphologies of droplets, the results of impacting could be divided into three types, stick to the fiber, merge and split into parts. The spreading factors and internal velocity distributions are obtained and analyzed. And the determination of regimes at these states is found. In addition, the droplets impact on hydrophobic fiber is also investigated.

Investigation on Cable Temperature in Wet Tunnel Considering Coupled Heat and Moisture Transfer

Many elder tunnels often lack waterproofing facilities, and water can easily accumulate in tunnel bottom or even on cable surface. Using the finite element method (FEM), the three-dimensional tunnel cable model, which couples the fluid field, the heat transfer and the moisture transport, is developed in our study. The coupling effects especially the phase change behavior are comprehensively considered. It indicates that a high humid environment would benefit the heat dissipation. Depending on the initial vapor content, water distribution, and cable arrangement, the maximum cable temperature may drop to some extent ranging from 2 °C to 10 °C. The presence of water changes the thermal properties of air, including the thermal conductivity and heat capacity. The latent heat caused by evaporation accounts for a greater portion compared to conduction. The presence of water changes the vapor concentration distribution of tunnel. It is mainly located near the cable surface within a distance of 0.02 m, and it decreases drastically away from the cable. In addition to common radial heat transfer, both the longitudinal and circumferential heat flux exists arising from the movement of fluid flow and water evaporation.

Nondestructive Testing of Bridge Stay Cable Surface Defects Based on Computer Vision

The automatically defect detection method using vision inspection is a promising direction. In this paper, an efficient defect detection method for detecting surface damage to cables on a cable-stayed bridge automatically is developed. A mechanism design method for the protective layer of cables of a bridge based on vision inspection and diameter measurement is proposed by combining computer vision and diameter measurement techniques. A detection system for the surface damages of cables is de-signed. Images of cable surfaces are then enhanced and subjected to threshold segmentation by utilizing the improved local grey contrast enhancement method and the improved maximum correlation method. Afterwards, the data obtained through diameter measurement are mined by employing the moving average method. Image enhancement, threshold segmentation, and diameter measurement methods are separately validated experimentally. The experimental test results show that the system delivers recall ratios for type-I and II surface defects of cables reaching 80.4% and 85.2% respectively, which accurately detects bulges on cable surfaces.

Evaluation Method of Surface Hydrophobicity Class of On-Board Cable Terminal Based on MSRCR-SPA-ResNet

On-board cable is an important electrical equipment of electric locomotive. In order to effectively evaluate the surface hydrophobicity class of on-board cable terminals and solve the problems of low identification efficiency and strong subjectivity of manual judgment of current detection methods, an evaluation method based on MSRCR-SPA-ResNet is proposed in this paper. Firstly, a data acquisition method of cable terminal surface hydrophobicity by spray method is proposed. Then, a data preprocessing method using MSRCR to reduce the interference of illumination angle on the feature extraction of cable terminal test image is proposed. The SPA structure is added to ResNet to form SPA-ResNet as the recognition model, which optimizes the multi-scale feature extraction capability of the model and improves the recognition accuracy of similar categories. Finally, a set of evaluation methods for the surface hydrophobicity class of on-board cable terminals are proposed. The experimental results show that this method can effectively distinguish the hydrophobicity class of the on-board cable terminal surface, and the recognition effect is better than the comparison scheme, and the attention characteristics of the recognition model to the test samples are basically consistent with the characteristics in the standard.

Published Papers Volume 30 - Issue 4 (Award Issue) Awarded Paper Use of insulation resistance imbalance degree for the condition assessment of power distribution cables

Medium-voltage (MV) underground power distribution cables are critical assets of The Hong Kong Electric Co., Ltd. (HK Electric) for ensuring reliable customer power delivery. The inspection and condition assessment of these power distribution cables are conducted regularly to determine their health. During diagnostic tests, all MV cables have to pass a threshold of insulation resistance (IR) before they can be energised. Low IR readings may indicate a deterioration in insulation related to a high leakage current. However, defining a threshold value to assess the intrinsic condition of the power distribution cables for every test is challenging. This is because the reference value is determined by several factors such as cable length, the composition of the cable circuit, e.g., cable type, number and types of cable joints, service years and surface leakage from cable splices and terminations. In order to tackle this problem, a concept of imbalance degree in IR testing is developed to supplement the existing tests on dielectric losses for the purpose of enhancing the condition assessment of three-phase power MV distribution cables when performing IR measurement. The effectiveness of this method has been validated with historical testing records of 11kV distribution power cables at HK Electric. Based on our experience and study results, this improved method could further enhance the diagnosis and maintenance efficacy of HK Electric’s power distribution cables.

An experimental study of dynamic icing process on an Aluminum-Conductor-Steel-Reinforced power cable with twisted outer strands

An experimental campaign was conducted to investigate the dynamic icing process on an Aluminum-Conductor-Steel-Reinforced (ACSR) power cable with twisted outer strands and characterize the resultant wind loads experienced by the power cable under both dry rime and wet glaze icing conditions. In addition to recording the dynamic icing process over the cable surface with a high-resolution imaging system, the three-dimensional (3D) shapes of the ice layers accreted on the cable model were also quantified by using a novel 3D profile scanning system. While the evolution of the wake flow behind the iced ACSR cable was quantified with a Particle Image Velocimetry (PIV) system, the variation of the wind loads experienced by the cable model was also examined based on the measurements of force/moment transducers. Under the dry rime icing condition, opaque, grainy ice was found to accrete only within the impinging zone of airborne water droplets over the cable frontal surface without any noticeable water runback flow over the cable surface. In comparison, substantial unfrozen water was observed to run back over the cable surface under the wet glaze icing condition, causing the formation of transparent, glazy ice layer over a much wider area over the cable surface. Correlating with the formation of more complicated glazy ice humps/horns over the ACSR cable surface, the accumulated ice mass was found to grow much faster during glaze icing process, in comparison to that of rime icing case. While the resultant wind loads acting on the iced ACSR cable was found to decrease gradually with the increasing icing time under the rime icing condition, the corresponding values were found to increase continuously under the glaze icing condition.

Three-dimensional defects detection of high-voltage cable joint based on iterative residual fitting

Aiming at the three-dimensional (3D) defects detection of high-voltage cables joint, a method based on iterative residual fitting is proposed. The 3D point cloud data was obtained by reconstructing the laser line projected onto the surface of the high-voltage cable joint. In order to remove noise generated by reconstruction which is located above or below the curve, a simple and effective strategy that the noise can be filtered by the gradient change in the neighborhood is adopted. Then a continuous iterative residual fitting method is proposed to effectively reduce the interference of the defect area on the curve fitting accuracy, thereby obtaining the accurate equation expression of the cable surface curve. By comparing the residual value of the high-voltage cable surface points relative to the fitting curve, the points of the defect area are marked. Finally 3D defect area is extracted through segmentation and clustering. Experiments have verified the effectiveness of the proposed method on artificial standard size defects and real manual ground defects. The absolute error of the depth (height) of artificial standard size defects is less than 0.05 mm. Compared with the traditional cylindrical fitting method, it can be seen that the recognition rate of the proposed method for manually ground defects of high-voltage cable joint is much higher than that of cylinder fitting method.

Adjustment Method of Coupled Dual-Surface Accuracy for Antennas Using Interval Model Updating

Affected by the uncertainties caused by cable cutting and assembly errors, material performance dispersion, and truss deformation, the dual-surface accuracy of a mesh antenna cannot satisfy the design requirements. However, the existing methods can only adjust the accuracy of a single surface. This paper studies a method for adjusting coupled dual-surface mesh antennas considering uncertainties. Dual-reflector mesh antennas use both the front and rear reflectors for sensing, and both surfaces have shape accuracy requirements. First, an interval model updating method based on sensitivity analysis is proposed to obtain an updated interval parameters model group, which can accurately represent the relationship between adjustment cable length and surface accuracy. Then, an interval optimization function for the coupled dual-surface accuracy is established to get optimal adjustment amounts, which is solved by using the fast elitist nondominated sorting genetic algorithm (NSGA-II). Meanwhile, a kriging model is introduced to improve the optimization efficiency. Finally, the AstroMesh antenna is taken as an example to verify the validity of the proposed method. The results show that both the front and back net accuracies can be improved after adjustment, proving the proposed method’s feasibility.

Simplified Model for Heat Transport for Cables in Pipes

This paper addresses challenges with modeling of heat transfer phenomenon for cables in duct or pipes when applying a numerical solution. Heat transport mechanisms between the cable and pipe surfaces are conduction, convection and radiation. Numerical calculation of convection when applying a finite element analysis (FEA), or other numerical tools requires heavy computation power and great skills of the program operator. In general, this is the most difficult part when modeling the heat transfer between the cable and the pipe surfaces and practitioners are often forced to use simplifications or approximate models. This paper introduces a simplified model where the contribution from convection is replaced by a heat source at the pipe wall and a corresponding heat sink at the cable. The phenomenon of air rising vertically in the tube resulting in the upper half of the pipe being heated more by convection than the lower half is also modelled. The simplified model is compared to both known models from thermodynamics, FEA including convection and laboratory as well as the full-scale field measurements. The simplified model shows good correspondence to both simulations and measurements, with the temperatures deviating by less than 1 °C.

Low Grating Lobe Cable-Network Reflector Antenna Design Using Integrated Structural-Electromagnetic Optimization Method

Geometric approximation errors of periodically distributed surface facets of cable-network reflector antennas can result in grating lobes undesired in some space missions. As the surface is shaped by the tensioned flexible cable-network structure, the electromagnetic (EM) and structural parameters are highly correlated, and the well-designed surface obtained only concerning the EM performance may not be shaped by the tension-only cable network with specified cable-tension constraints. To address the problem, this study proposes an integrated structural-EM optimization method to enable low grating lobe cable-network antenna design. In this method, force densities of the cables, which can determine both the cable tensions and surface node positions that decide the boundary conditions of the EM field, are selected as the design variables. An adaptive objective/constraint function is proposed, which enables the grating lobe level (GLL) to be minimized with constrained cable tensions, antenna gain, and first sidelobe level (SLL) in a simultaneous, feasible and relatively fast way. To demonstrate the feasibility and effectiveness of the proposed method, it was implemented on a 12 m-diameter cable-network antenna. The results indicate that the grating lobes are greatly degraded and the achieved surface can be formed by well tensioned cables.

CCRobot-IV: An Obstacle-Free Split-Type Quad-Ducted Propeller-Driven Bridge Stay Cable-Climbing Robot

This letter presents CCRobot-IV, the fourth version of a climbing robot designed for bridge cable-inspection tasks. CCRobot-IV inherits design features from the previous CCRobot series, and has improved capability for crossing cables with obstacles such as helical ribs, small metal accessories, and various other obstacles. CCRobot-IV consists of a quad-ducted propeller-driven climbing precursor and an affiliated payload-carrying body. Because a quad-ducted propeller does not depend on friction generated by mutual contact and extrusion, the precursor’s locomotion is decoupled from the surface of the bridge cable and the obstacles on it. When the precursor climbs up to reach the set position, it uses its gripper’s self-locking palms to grasp the bridge cable, which creates a fixed anchor point that allows the payload-carrying body to pull itself up using wires and two winches (which are a type of driving wheel that do not require extrusion force on the cable to produce adhesion and friction). Therefore, the robot’s payload capacity is also decoupled from adhesion to the cable surface, and thus the entire system has obstacle-free operation. Experimental tests and field tests have demonstrated CCRobot-IV’s climbing performance, payload capacity, and potential application utility.

Theoretical analysis and design of fire protection and thermal insulation of parallel wire or strand cables

In this study, a transient heat flow model has been established for parallel wire or strand cables at high temperature by employing the lumped thermal mass approach, and the numerical solution of the surface temperature as a function of time in each layer of the steel wire or strand inside the cable was calculated. Accuracy of the theoretical method is verified through uniform heating test of 73Φ15.7 mm steel strand cable. The results calculated show that temperature field inhomogeneity of cable section is overestimation on the condition that heat conduction inside the cable is not considered. Considering heat conduction or not, the maximum temperature difference of the core steel stand at the same time point is 373 . Unprotected 73Φ15.7 mm cable is damaged in only 12 min in UL1709 fire, and arrangement of fire protection layer around cable can effectively retard the temperature rise of cable surface. The experimental results are in good agreement with the theoretical calculation values in early stage of fire, and the temperature difference between the two is within 10%. Besides, the numerical calculations were analyzed in accordance with the fire protection requirements limiting the surface temperature of cables. It was observed that the minimum thickness of the fire protection layer required to meet the PTI DC45.1-12 standard was linearly related to the numerical value of the section factor of the outermost layer of steel wires or steel strands in the equivalent model, and the slope of the function was approximately equal to the conduction coefficient of fire protection layer, as the cable was subjected to fire for 30 min. Further, based on this, a simple method was proposed to calculate the minimum thickness of the fire protection layer for parallel wire or strand cables.

Optimization of Multiple Helical Fillets Surface to Suppress Rain-wind Vibration of Stay Cables: A Wind Tunnel Investigation

Aims: To develop a new cable surface for control rain wind induced cable vibration of stay cable. Background: Stay cables are light and vulnerable structures. Therefore, it can be easily excited by wind or rain wind interaction. Stay cables wrapped with a single helical fillet have been proposed so far. However, these countermeasures could prevent cable vibration well, especially in dry conditions. Objective: Therefore, the objective of this research is to develop a new cable surface to control not only RWIV but also dry galloping of stay cable. Methods: A wind tunnel test will be used to investigate the RWIV characteristics and its new countermeasure. Results: First, a rain wind-induced vibration of circular stay cable was reproduced in a wind tunnel environment. The effect of upper and lower water rivulets was examined to understand their role on RWIV better. A rainfall simulator was employed to generate artificial rainfall for two different wind tunnel experiments. Finally, to control the RWIV of stay cables, novel multiple helical surface fillets were used. The upper and lower rain rivulets can play a significant role in energizing the RWIV. It was also found that the multiple helical surface fillets can suppress the cable vibration well both in wet and dry conditions. Conclusion: Multiple helical fillets cable surface could successfully prevent both the RWIV and dry galloping. To fabricate helical fillet cable to control cable vibration, 04 to 12 fillets with sizes ranging from 3mmx7.5mm to 5mmx7.5mm and a pitch of 2.95D-4.78D (D: cable diameter) are the most influential parameters and suggested herewith for practical application.