Cable Temperature Research Articles

Ampacity derating factors for submarine transmission cables in J-tubes

With the development of deep-sea wind power, the temperature hotspots of submarine cables in J-tubes are getting increasing attention. Currently, the relevant standards do not provide a thermal rating method for such cable sections, and the only studies are difficult to apply in practice. This study derived an analytical solution for calculating the derating in ampacity of submarine cables within J-tubes. The proposed approach is efficient and readily integrated with IEC-related standards. Initially, an indoor experiment was conducted to validate the correctness of the analytical model. Subsequently, a numerical example utilizing an actual HVDC submarine cable is presented, demonstrating increased cable conductor temperature within the J-tube and a corresponding reduction in ampacity. A derating factor is employed to quantify the extent of ampacity reduction, which is a function of the J-tube length, outer diameter, ambient temperature, wind speed, and solar radiation intensity. It turns out that once the J-tube air section's length exceeds approximately 60 times the cable outer diameter, the transmission circuit ampacity can be based on the value installed in the infinite J-tube. Furthermore, factors resulting in substantial cable ampacity reduction, such as high solar radiation intensity, may yield a derating factor approaching 0.6.

Experimental investigation into thermal characteristics of subcooled flow boiling in horizontal concentric annuli for cooling ultra-fast electric vehicle charging cables

In an effort to reduce the charging time of electric vehicles (EVs), the thermal management of the charging system has emerged as one of the most urgent issues. The charging rate has been restricted to avoid thermal failure especially in charging cable. Recently, a direct contact cooling technique that utilizes subcooled flow boiling for charging cables has been proposed and has shown promising thermal management performance. However, there has been a lack of clear explanation regarding its thermal characteristics due to its intrinsically complicated flow features. This study investigates the thermal characteristics of subcooled flow boiling in a horizontally aligned concentric annular tube intended to simulate the direct contact cooling technique employed for charging cables. For the experimental investigation, the wall temperature measurements and high-speed flow visualization images acquired from the transparent test module annulus, with inner and outer diameters of 6.35 mm and 22.0 mm, were utilized. Three key axial thermal characteristics of subcooled flow boiling in annulus have been analyzed, and they are flow regime transition, variation of heat transfer mechanisms, and occurrence of critical heat flux (CHF). The transition of flow regimes and the variation of dominant heat transfer mechanisms in the axial direction are mutually influencing due to the coupled effects between the hydrodynamic and thermal characteristics of simultaneously developing flows. The flow regime changes from partially developed boiling (PDB) to fully developed boiling (FDB) as the intensities of nucleate boiling and bubble recondensation vary in the axial direction, while the dominant heat transfer mechanism shifts from single-phase convection to nucleate boiling, corresponding to the flow regime transition from PDB to FDB. The departure from nucleate boiling (DNB) type CHF is observed, manifested by the wavy interface propagating from the far downstream to the upstream region, and the intensities of nucleate boiling and bubble recondensation are also identified as the dominant parameters in determining the occurrence of CHF. Charging time estimation reveals that the proposed method can achieve an 80 % charge for 100-kWh EV batteries in 98 s, while maintaining the cable wire temperature below the safety limit of 80 °C. This strongly supports its potential as a promising thermal management technique for future ultra-fast charging systems.

Short-Circuit Conditions and Thermal Behaviour of Different Cable Formations

Modern electrical installations widely use cable formations consisting of a few single cables connected in parallel. In this article, the short-circuit problem is analysed with its influence on cable temperature. In the assumed case study of supply lines, five equivalent cases were considered. Calculations of temperature increase during faults were performed using a simplified method and FEM model. This study shows the differences in calculation methods and points to better solutions in cable arrangements due to safety and operating conditions in cases of faults. Additionally, some problems in the simplified method were identified and pointed out in the range of its application.

Temperature Evaluation Considering Gradient Distribution for MV Cable XLPE Insulation Based on Wave Velocity

Temperature is an important factor for the service life of cable insulation. To ensure safety, the operating temperature of cables must be monitored. Since optical fiber temperature measurement technology is difficult to be used widely in medium voltage (MV) cables due to cost, this paper proposes a temperature evaluation method based on wave velocity. Firstly, the dielectric constant of cross-linked polyethylene (XLPE) cable insulation under different temperature is obtained through experiment. Based on the result, the relationship curve between wave velocity and temperature is established. The asymmetry effect due to temperature gradient in the cable insulation is discussed via finite element simulation. The effectiveness of obtaining the average insulation temperature of the cable based on wave velocity is validated. In addition, the mechanism of the temperature influence on the cable insulation material’s dielectric constant is analyzed by molecular dynamics simulation, which further deepens understanding of the characteristics of cable insulation materials.

Calculation of cable core temperature and cooling method of submarine cable

Calculation of cable core temperature and cooling method of submarine cable

Power cable monitoring method based on UHF‐RFID and deep learning in edge computing environment

AbstractThis research addresses the challenge faced by most existing prediction methods in handling nonlinear data of cables. Furthermore, it proposes a novel power cable monitoring method utilizing UHF‐RFID and deep learning within an edge computing environment, specifically targeting the currently suboptimal wireless monitoring of cables. First, based on edge computing, a power cable monitoring system is designed to migrate the analysis of massive data to the edge of the network to improve the monitoring efficiency. Then, the temperature sensing chip and RFID chip were integrated to design a UHF‐RFID temperature tag, which was fixed at the cable temperature measurement point to achieve passive wireless monitoring of the cable. Finally, the parameters of the GRNN model are optimized using the beetle antennae search algorithm, and the EEMD decomposed data is input into the BAS‐GRNN model for learning to output temperature prediction results. Based on the establishment of an experimental platform, the method was demonstrated, and results showed that the maximum error between the UHF‐RFID temperature tag temperature measurement results and the thermocouple was within 0.3°C, and the average relative error of the proposed method was only 0.01, which can meet the accuracy requirements of actual monitoring of power cables.

Unsteady heat transfer of long gas insulated transmission lines in tunnel: Model and analysis

The temperature of the cable core and cable casing is crucial for the safety and efficiency of the transmission system. Accurately predicting the distribution and variation of the transmission temperature field in the gas insulated transmission lines (GIL) tunnel is essential to ensure the long GIL tunnel transmission system's safe and stable operation. This paper addresses the challenge of calculating unsteady heat transfer flow in extra-long GIL transmission tunnels. The paper proposes a model, and a rapid solution method for extra-long GIL transmission heat transfer flow. In addition, the temperature variation during the operation of 1000 kV GIL has been analyzed. The results indicated that the conductor and cable casing temperature gradually increases and tends to be relatively stable with the operation time. The research results can provide theoretical basis and data support for the regulation of GIL tunnel transmission operation.

Enhancement of the underground cable current capacity by using nano‐dielectrics

AbstractIn most underground power cables, cross‐linked polyethylene (XLPE) is utilized as the main insulating material, while polyvinyl chloride (PVC) is usually used as a nonmetallic sheath or jacketing for the cable. Accordingly, improving the electrical and thermal characteristics of these materials leads to an increase in cable dielectric strength, besides a rise in the current capacity of the underground power cables. Thus, enhancing the thermal characteristics of cable insulation is the goal of many research studies. In this regard, increasing the current capacity of underground power cables is an essential topic for electrical distribution and transmission networks. This usually occurs by increasing the cross‐sectional area of the cable conductor, which means raising the cost of transmitting electrical energy. Another proposed alternative may be to improve the thermal properties of the dielectric material using nanotechnology to allow better dissipation of heat resulting from the cable losses. This article proposes the use of nano‐composite dielectrics to increase the current capacities of underground power cables. Nano‐fillers are used to enhance the thermal and electrical characteristics of XLPE and PVC, which represent cable dielectric materials. Accordingly, in this paper, many experiments are conducted on various nano‐dielectric materials to choose the most appropriate nano‐dielectrics for improving both the thermal and electrical properties. Hence, measurements are performed on the thermal and electrical properties of dielectric nano‐materials manufactured in the laboratory. Further, calculations of the cable's current capacities by the use of the measured properties of nano‐dielectrics are done considering several backfill soils. From the obtained measurements and calculations carried out on cable capacities, it is concluded that the use of XLPE/ZnO 5 wt.% as the insulation and PVC/ZnO 5 wt.% as the jacket material increased the cable current capacity by 6.2% for a cable of 33 kV rating, 9.2% for 66 kV cable, and 15.7% for 220 kV cable when wet clay is used as backfill soil. From the calculations carried out it is found that the use of nano‐composite dielectrics reduces the temperature of the cable components by significant values. For example, the core temperature of the 33 kV cable is reduced by 15.6°C, while for the 66 kV cable, the cable core temperature is decreased by 12.6°C, and for 220 kV the conductor temperature is reduced from 71.3°C to 58.3°C when each cable is loaded by its rating.

A digital twin model of the axial temperature field of a DC cable for millisecond calculations

The most important features of digital twin technology for transmission and transformation equipment are symbiotic evolution and state prediction. In constructing the digital twin model for DC cables, the transient and steady-state temperature fields need to be considered comprehensively in the modeling process to consider the multi-physical field coupling, mathematical model, operational data, and environmental conditions in specific cases, which makes it difficult to satisfy the real-time requirements of the digital twin. To solve this problem, in this paper, a digital twin technology architecture for DC cables is proposed, and a neural network learning model is constructed to minimize the latency due to the complexity of the model simulation. Moreover, an efficient digital twin model that is based on the model-driven approach is developed for the fast computation of the axial temperature field of DC cables. The use of the Sequence-to-Sequence residual neural network algorithm for the reduced-order multi-physics field coupling modeling reduces the computational time and ensures as much accuracy as possible up to the finite element model simulation. The simulation results show that the use of the digital twin model reduces the simulation time from 275 s to 0.56 s, and the relative error between the accuracy of the digital twin model and the finite element model for the axial temperature field of the DC cable is 0.46 %. Finally, verification of the reasonableness and feasibility of the proposed method is carried out via an experimental platform according to the standard of CIGRE TB496. In particular, the maximum value of the DC cable temperature is verified to have a small error compared with the result of the Sequence-to-Sequence calculation under specific working conditions.

Research on the application of WO3 gas sensor based on noble metals modification in cable fire detection

In the monitoring of cable fire, it is of great significance to be able to conduct early fire warning, which requires that sensors have high sensitivity to the cable vapors at low temperatures. In this study, WO3 thick films modified with Au, Pd, and Pt single or bimetallic nanoparticles were fabricated via magnetron sputtering. Gas sensors utilizing these materials exhibited significant response to the low-temperature vapor emitted by YJV22 and YJY23 cables. Among them, Pd/WO3-20 demonstrated a response value of 20 to the vapor of 81[Formula: see text]C YJV22 cables, marking a remarkable 6.3-fold increase compared to pure WO3, and the response time was 13 s. Similarly, Pt/WO3-10 exhibited a response value of 11.11 to the vapor of 104[Formula: see text]C YJY23 cables, representing a 6.9-fold enhancement over pure WO3 with a response time of 12 s. The heating temperature of cables remains below their critical threshold, indicating that it is in the early stages of cable fires, the findings hold significant implications for early warning systems designed to detect cable fires promptly.

Alternative Concepts for Extruded Power Cable Insulation: from Thermosets to Thermoplastics.

The most common type of insulation of extruded high-voltage power cables is composed of low-density polyethylene (LDPE), which must be crosslinked to adjust its thermomechanical properties. A major drawback is the need for hazardous curing agents and the release of harmful curing byproducts during cable production, while the thermoset nature complicates reprocessing of the insulation material. This perspective explores recent progress in the development of alternative concepts that allow to avoid byproducts through either click chemistry type curing of polyethylene-based copolymers or the use of polyolefin blends or copolymers, which entirely removes the need for crosslinking. Moreover, polypropylene-based thermoplastic formulations enable the design of insulation materials that can withstand higher cable operating temperatures and facilitate reprocessing by remelting once the cable reaches the end of its lifetime. Finally, polyethylene-based covalent and non-covalent adaptable networks are explored, which may allow to combine the advantages of thermoset and thermoplastic insulation materials in terms of thermomechanical properties and reprocessability.

Research on denoising the temperature monitoring signal of a distributed optical fiber downhole cable

Aiming at the noise mixed in the downhole cable skin temperature signal measured by the BOTDR distributed fiber optic sensing temperature measurement system, a new improved wavelet threshold function is proposed, and denoising experiments are completed based on the MATLAB platform for the measured cable skin temperature signal. The denoising results of several threshold function methods are compared and analyzed from the aspects of graphical intuitive comparison as well as quantitative evaluation indicators. The results show that the improved threshold function denoising fiber optic temperature monitoring signal has a higher SNR and lower RMSE, there is no obvious distortion phenomenon, and the denoising performance is significantly improved compared with the traditional threshold function, which has a high application value.

Research on Temperature Sensing Method for Three-Core Cable Intermediate Joint Considering Three-Phase Load Imbalance

Temperature is a key factor affecting the insulation performance and operation safety of cable joints. Accurate acquisition of hot spot temperatures of cable joints is a difficult issue in cable operation and maintenance. Three-core cables may have unbalanced three-phase loads in actual operation. This paper takes a 10 kV three-core cable joint as the research object; based on the temperature field numerical simulation method, it analyzes the diffusion path of the main heat flow inside the joint and establishes an inversion model that fits the hot spot temperature of the joint through the surface temperature of the cable body. At the same time, considering the special situation of the unbalanced three-phase load of a three-core cable, the joint hot spot temperature inversion model of a three-core cable under an unbalanced three-phase load is further established. This paper further uses the cable joint multi-step unbalanced load temperature rise test to verify the accuracy of the cable joint hot spot temperature inversion model. The maximum error of the transient hot spot temperature inversion does not exceed 4.5 °C, and the steady-state error is within 3 °C. A higher inversion accuracy was achieved. The research results of this article can provide a reference for real-time monitoring of the hot spot temperature of cable joints.

Exploration of Temperature Inversion in Intermediate Joints of 10 kV Three-Core Cable

In order to precisely ascertain the temperature at the hot spot within the intermediate joint of a three-core cable, this study focused on a 10 kV three-core cable joint as its primary subject. A three-dimensional finite element model of the cable joint was constructed, enabling the calculation of both the steady-state hot spot temperature field distribution and the transient temperature rise curve of the joint. Employing a one-dimensional transient thermal path model for the cable body, a radial inversion model for the cable core temperature was established. Through simulating the transient temperature field of the cable joint under varying currents, a fitting relationship was determined for the axial temperature points of the cable core. Subsequently, an inversion perception model was devised to calculate the hot spot temperature of the cable joint based on temperature measurements at specific points on the outer surface of the cable. Under both continuous and periodic loads, the inversion results revealed a consistent trend in the temperature at the joint crimping point with the finite element calculation outcomes, demonstrating a maximum error of within 3 degrees Celsius. This verification underscores the precision of the temperature combination inversion method when applied to three-core cable joints.

Direct Air Cooling of Pipe-Type Transmission Cable for Ampacity Enhancement: Simulations and Experiments

Amid the growing demand for energy supply in modern cities, the enhancement of transmission capacity is receiving considerable attention. In this study, we propose a novel method of direct forced cooling in pipe-type transmission lines via an external air supply for reducing the cable temperature and enhancing the ampacity. We conducted numerical simulations using computationally efficient two-dimensional models and a reduced-length three-dimensional model for assessing the cooling efficiency, the distance required for temperature convergence, and the fan/pump capacity required for forced air cooling. We found a 26% increase in ampacity in the case of 5 m/s inlet air velocity into the pipe conduit. We also built and tested the experimental setup equipped with a 300 m length model transmission cable. Results of the forced air cooling experiments show good agreement with numerical simulations. To the best of our knowledge, this study demonstrates the first analysis and validation of direct cooling in pipe-type cables, presenting a promising path for efficient power management in modern metropolitan areas.

Evaluating and forecasting methods for assessing the health status of cables under the load of large-scale electric vehicle charging

The assessment of the health status and prediction of the lifespan of cable equipment are critical for ensuring the stability and efficiency of the power grid. This paper develops a temperature-current-capacity-life calculation model for cables, considering the fast and slow charging demands of electric vehicles (EVs). Analyses under scenarios of rapid and slow charging demands are conducted, introducing a cable health index and establishing a health status assessment framework based on this index. The framework accounts for various factors leading to cable faults, offering a comprehensive evaluation of the health status of cables with different fault rates. Building upon this, a prediction method using the Fire Hawk Optimization (FHO) Algorithm and Convolutional Neural Network (CNN) is proposed. This method enhances performance by optimizing the hyperparameters of Bidirectional Gated Recurrent Unit (BiGRU) through FHO, effectively searching and determining the optimal hyperparameter configuration. The impact of different scenarios and varying EV penetration rates on cable temperature is analyzed through case studies, facilitating the assessment and prediction of health status.

Notice of Removal: Thermal Analysis of Multiple Cable Crossings

This paper proposes a new approach for calculation of cable temperatures when power cables cross other heat source, including other power cables. Such situations occur more and more often in a congested urban environment or in the vicinity of substations. The method allows analysis of large number of cables in one location and does not require a predetermination of the hottest point in the installation. The latter requirement has been a real limitation of the procedures published up to now. The proposed procedure, based on nodal analysis, is illustrated through several numerical examples and the results are compared with the finite element analysis (FEA).

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. The traditional method of calculating the internal temperature of cables suffers from low accuracy and time-consuming problems. Methods To quickly and accurately calculate the cable’s internal temperature, 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 is established using the exponential function. The cable surface temperatures under five operating conditions are measured online and compared with the calculated results of the temperature mapping model. Results Under five operating conditions, the average absolute error of the proposed model is 0.628 °C, and the average calculation time is 0.005 s. The average absolute error of the traditional model is 0.635 °C, and the average calculation time is 201.86 s. Conclusions The temperature mapping model developed in this paper can quickly and accurately calculate the cable’s internal temperature and forms an important part of the digital twin model of the cable.

Optimal design of liquid cooling structures for superfast charging cable cores under a high current load

Superchargers have become a focus of much research into new-energy vehicles, for which the cooling of high-current cable cores is a key problem that needs to be solved. To estimate influences of different core structures of liquid-cooled cables on the fluid flow and heat transfer characteristics in circular pipes, nine helical cable core structures with insertion of smooth pipes were designed taking dimethyl silicone oil as the coolant. The fluid flow and heat transfer in the pipes were studied through computational fluid dynamics (CFD) numerical simulation at different inlet velocities (0.2–2.0 m/s), and the models were verified by building an experimental platform. Numerical calculation results show that under conditions of the same Re and pitch of cable cores, the average surface temperature of three-core cables is lower than those of single-core and double-core cables. Moreover, the mean flow velocity v in pipes, heat transfer performance Nu, resistance factor f, evaluation factor for comprehensive heat transfer performance (PEC), and field synergy number Fc all increase with the decrease in the pitch of cable cores. This finding indicates that the heat transfer effect is gradually enhanced. The research implies that when the pitch p is 22.4 mm (cable C6), the velocity field is the most synergetic with the temperature field and the comprehensive heat transfer performance is optimal. This research provides an excellent cooling scheme for cable cores in superchargers under a high current load.

Experimental study of the temperature characteristics of the main cables and slings in suspension bridge fires

Fire raises key issues in the safety assessment and thermal protection of a suspension bridge, where the temperature profile of the main cables and slings (cable) is an important parameter that has not been quantified in previous studies. The present research investigated its evolution in fire scenarios on the emergency lane and inside lane. A suspension bridge fire experiment platform was built, and 30 sets of pool fire tests simulating vehicle fire were conducted considering the wind velocity, pool size, and pool location. The focus was on the mass burning rate of gasoline and the temperature profile of cables during fires in different lanes. The results showed that the mass burning rate increased with pool size and cross-wind. A new characterization of the gasoline burning rate was introduced. A vehicle fire in the emergency lane posed a greater thermal threat to cables than an inside-lane fire. An exponential model representing the temperature profile of cables was derived. A uniform prediction model for the maximum temperature of cables exposed to different lane fires on a suspension bridge was proposed for the first time. The predicted values of proposed model were compared with measured maximum temperature, and reliable results were obtained.