Cable Temperature Research Articles

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.

Investigation of effect of laying and bonding parameters of high-voltage underground cables on thermal and electrical performances by multiphysics FEM analysis

High-voltage underground cable systems are one of the critical systems used in the distribution of energy. During the design phase of these systems, important issues are to be considered, such as screen voltages, screen currents, thermal calculations, and power losses. If these issues are not considered properly, the system’s reliability and efficiency can be seriously reduced. In high-voltage underground cable systems, current carrying capacity and power losses vary according to the screen bonding type, the phase sequence, the distance between the cables, and the number of parallel systems. A detailed analysis is required during the system design phase in this context. In this study, electrical and thermal analyses of a cable system consisting of two parallel group were carried out according to different design parameters, and the performances of different system designs were evaluated. Trefoil and flat layouts were used in the analyzed systems. In addition, the structure of the single-side and solidly bonded systems was also examined. While carrying out the investigations, the variation of the distance between the cables according to three different parameters was also discussed. In total, 56 different scenarios were created, and the systems’ performances were examined. Screen currents, screen voltages, cable temperatures, and power losses were considered while conducting the investigations. In this context, coupled electrical and thermal calculations were performed in the Ansys Electronics Suite finite element software. Additionally, the study utilized the CymCap program to verify the finite element model created, with analytical analyses conducted in accordance with IEC 60287 standards. The significance of these calculations cannot be overstated, as the analysis results demonstrate the direct impact of various design parameters on the system’s overall performance.

Analytical Thermal Cable Model for Bundles of Identical Single Wire Cables

Overcurrents may lead to critical temperatures in cable systems. Fuses can protect the cable insulation from damage. As the classically used melting fuses cannot fulfill the growing requirements concerning diagnosis, reset behavior, or fail safety, electronic fuses based on power transistors are more and more introduced in modern systems. As reliable temperature measurements are complex, the electronic fuses are often controlled by the electrical currents flowing through the semiconductor by, e.g., a microcontroller. On the microcontroller the cable temperature is estimated from the current based on an electrothermal cable model. When the temperature exceeds a given threshold the transistor interrupts the current flow. Therefore, accurate and computationally simple thermal cable models are necessary. Complex numerical solutions are inappropriate. For single wire cables several calculation methods are known already, for arrangements of several wires with insulation these methods are not accurate enough. This article presents an analytical thermoelectric calculation method for multiconductor cable arrangements consisting of several identical single wire cables. An approach for the determination of important model parameters is presented and the final model is validated for a power over data line application. The model is exemplarily applied for calculating the temperature developments and ampacities in cable bundles consisting of a different number of cables and for the comparison between a solid and a stranded cable.

Thermal analysis of the influence of harmonics on the current capacity of medium‐voltage underground power cables

AbstractIn this article, an algorithm is proposed and used to study the influence of harmonics on the behavior of medium‐voltage underground cables in flat formation. The proposed algorithm is a thermal model based on the heat equilibrium of the thermal circuit nodes of the medium‐voltage cable system. The impact of harmonics on the temperature rise of the cable elements and the cable capacity is evaluated in this article. Also, the impact of harmonics on the derating factors of cable for different soil types is presented. Finally, the measurement of temperatures of cable cores is carried out experimentally and compared with the calculated results to validate the proposed algorithm. One of the algorithm merits is that several harmonic percentages can be taken into account for each cable phase individually, and the heat exchange between the cable phases and their sheath is also taken into consideration. From the obtained results, it is illustrated that the presence of harmonics has a remarkable influence on the cable core temperature; mainly, harmonics of the third and fifth orders may lead to dry zone formation around the cable. It is also observed that the presence of harmonics has an important influence on the cable current, especially when it is buried in soil that has high thermal resistivity during the summer season (suction tension = ∞). In summer, the cable core temperature reached 152.162°C, 139.053°C, and 133.375°C when lime, sand, and silty sand, respectively, are used as backfill materials, rather than 90°C in the normal operating condition of the 11 kV three‐phase single‐core cable. It is observed also that with the increase of the soil thermal resistivity, the ratio of /) reached about 1.2 times at 2.5 K m/W soil thermal resistivity. In addition, it is also observed that the impact of harmonics leads to a percentage reduction in the derating factor of the cable center phase by 11.88%–12.37% depending on the composition of the backfill materials.

Local Temperature Reduction in Thin Wire Cables Due to Contacted Thermocouples

Complex cable systems for various applications need to be protected from over-current-induced high temperatures. That is why the cable temperature has to be monitored. Temperature measurement especially in thin wire cables can be challenging. Many measurement approaches only allow the surface temperature measurement and therefore are not appropriate for monitoring the inner cable temperature. Others, such as the widespread thermocouple temperature measurement, can relevantly change the cable temperature and therefore lead to deviations between the measured temperature and the real cable temperature without connected measurement equipment. This effect is studied in this article. For comparison, an indirect temperature measurement approach is presented that is based on the cable’s resistance measurement. Subsequently, the temperature drop due to a connected thermocouple is measured. An analytical model for the description of this effect is proposed and validated. Finally, based on parameter studies, a rule for selecting suitable thermocouples is derived.

Planning of Optimal Operation Scheme for Ventilated Tunnel Fans Based on Cable Conductor Temperature

With the increasing construction of underground power cable tunnels for energy transmission, the fans in tunnels, used for ventilation, consume great deal of electric energy. Due to the lack of scientific planning, a large number of energy is unnecessarily consumed. This paper proposes an optimal planning method for fan operation based on cable conductor temperature. The improved flow field parameters are used to calculate the cable temperature, which is validated by finite element method (FEM). The conductor temperature is then taken as the constraint condition for fan operation planning. Based on the load forecasting, a variety of fan operation schemes are obtained. The improved particle swarm optimization (PSO) algorithm is implemented to obtain the optimal operation scheme such that the cable conductor temperature does not exceed the allowable value and the fan power consumption is minimum. The energy consumption of the fan after planning is only 18.1% of the original one in the best case for the studied scenario. To solve the load forecasting error problem, this paper adopts model predictive control (MPC) to replan the optimal operation scheme of the fan dynamically. The results show that the optimal planning scheme can always be guaranteed.

Integrated physical and probabilistic modelling of low voltage cable temperatures, stress cycles and damage

Integrated physical and probabilistic modelling of low voltage cable temperatures, stress cycles and damage

Cable Temperature Prediction Based on RF-GPR for Digital Twin Applications

With the wide application of power cables in the field of transmission and distribution and the increasing emphasis of power departments on the reliability, safety and stability of power cable operation, how to more accurately and quickly analyze the temperature distribution of power cables and how to evaluate the running state of power cables have become research hotspots. Through the combination of finite element calculation and the artificial intelligence method, an innovative method of digital twin cable temperature prediction based on RF-GPR is proposed in this paper. Firstly, the finite element method is used to calculate the coupling of the electromagnetic field and temperature field of a 10 kV AC cable laid in the cable trench, and a certain amount of basic data are provided through the finite element calculation results. Then, using the basic principle of the random forest (RF) variable importance score, the RF-GPR cable temperature prediction model is constructed using the series hybrid model and Gaussian process regression (GPR), the model prediction results are compared and analyzed, and the calculation time is improved by about 1500 times. Finally, a digital twinning platform for cable temperature calculation based on RF-GPR is designed, which provides technical support for the application of digital twinning.

Temperature and humidity sensor monitoring of directly buried cable based on temperature field distribution simulation of power cable

Power cable is a piece of major transmission equipment, and its operating temperature as a major factor determines whether the cable system can operate safely and reliably and the current-carrying capacity. Therefore, it is of great significance to master the real-time temperature and the distribution of the power cable core. During the aging of cable insulation, temperature, as a major factor, directly determines the aging rate. One of the basic parameters on the power cable is the ampacity. If the ampacity is high, the cable will be overloaded. In this paper, the thermal circuit method is used to construct and calculate the cable, and the whale algorithm is used to estimate the temperature of the cable conductor. The conductor is estimated accurately within the allowable error range. The results are compared with the results of finite element simulation to verify the effectiveness of the finite element method. Through the experimental analysis, the model is established according to the cable trench on the spot. The steady-state temperature field is calculated through parameter setting. The average packet loss rate is 0.066 %, and the relative error is 0.32 %, which proves that this study can optimize the communication mode of the network and achieve a better monitoring effect. The method realizes the real-time temperature rise prediction of the cable core conductor by using the temperature rise of the outer skin. It can provide a certain theoretical basis for the online monitoring and engineering practical application of the cable core temperature and has practical significance.

Investigation of the Temperature Actions of Bridge Cables Based on Long-Term Measurement and the Gradient Boosted Regression Trees Method

Cable-stayed bridges have been commonly used on high-speed railways. The design, construction, and maintenance of cable-stayed bridges necessitate an accurate assessment of the cable temperature field. However, the temperature fields of cables have not been well established. Therefore, this research aims to investigate the distribution of the temperature field, the time variability of temperatures, and the representative value of temperature actions in stayed cables. A cable segment experiment, spanning over one year, is conducted near the bridge site. Based on the monitoring temperatures and meteorological data, the distribution of the temperature field is studied, and the time variability of cable temperatures is investigated. The findings show that the temperature distribution is generally uniform along the cross-section without a significant temperature gradient, while the amplitudes of the annual cycle variation and daily cycle variation in temperatures are significant. To accurately determine the temperature deformation of a cable, it is necessary to consider both the daily temperature fluctuations and the annual cycle of uniform temperatures. Then, using the gradient boosted regression trees method, the relationship between the cable temperature and multiple environmental variables is explored, and representative cable uniform temperatures for design are obtained by the extreme value analysis. The presented data and results provide a good basis for the operation and maintenance of in-service long-span cable-stayed bridges.

Моделирование теплового старения кабельной полимерной композиции на основе этиленвинилацетата

The aging of a cable polymer shell composition based on ethylene vinyl acetate has been studied. During accelerated aging tests in the temperature range from 110 to 150 °С, the change in the mechanical and thermal properties of the elastomeric samples was monitored. The sample properties were controlled by measuring the following characteristics: the relative elongation at break (REB), the indentation modulus of elasticity (IME), the oxidative induction temperature, and the oxidative induction time. To simulate a REB change during the aging, an empirical kinetic equation was used, which reflects the three stages of elastomer aging: finish cross-linking, inhibited oxidation and non-inhibited oxidation. The developed model was validated, and a forecast of the REB of the shell elastomer for the maximum operating temperature of low-voltage cables’ operation, stipulated by technical documents is presented. The possibility of a non-destructive testing and prediction of the cable state, using IME is demonstrated. A system of models associated with each other with common physical parameters has been developed. It includes both the models describing a change in the mechanical properties in the course of the thermal aging and the thermal-oxidative parameters of the polymer composition based on ethylene vinyl acetate.

Effect of Space Charge on Stationary and Transient Electric Field Distribution of HVDC Cable Joint

The conversion of AC XLPE cable lines into direct-current (DC) operation has been proven to be an effective means to improve the transmission capacity of the system. Prefabricated joints are the weakest points of a cable line because of the complex structures, and composite interfaces contained. Therefore, it is of great theoretical and engineering significance to study the field strength distribution of XLPE AC cable prefabricated joints under DC voltage, effectively evaluate their DC tolerance characteristics, and provide a basis for the construction and transformation of XLPE cable DC distribution network system. This paper takes the silicone rubber (SIR), and ethylene-propylene-diene monomer (EPDM) prefabricated joints of 10kV XLPE cables as an example, the cable joint temperature field, and electric field coupling simulation model is established by the finite element analysis software COMSOL Multiphysics. The steady and transient electric field simulation of the joints under different DC voltages and load conditions are carried out considering the influence of space charge. The results show that with the increase of applied voltages and load level, the space charge injection increases, and the maximum steady state field strength in the joint is concentrated at the root of the stress cone, showing an increasing trend. Compared with the SIR joint, the field strength in the EPDM joint is higher. The capacitive component of the field strength in the joint is proportional to the peak value of the impulse voltage under the DC superimposed impulse voltage. In other words, the transient electric field equation meets the superposition principle applied.

Rapid calculation model for transient temperature rise of complex direct buried cable cores

Actual direct buried cable is a complex model that contains backfill sand and external soil. To improve dynamic load level and utilization of buried power cables, it is crucial to quickly calculate power cable core temperature under sudden changes in load. The complex buried cable structure is decomposed into three parts so as to improve the accuracy of calculation. These three parts are the cable body, the backfill sand and the external soil, which temporary temperature rise can be solved by respect transient thermal circuit models separately and then add them up to obtain the cable core temperature. In actual project, the values of the transient thermal circuit model elements can be solved in advance and made into a table, and the relevant parameters can be obtained by checking the table in use. The backfill sand is only related to its heat conductivity, the external soil is related to its heat conductivity and burial depth. There transient thermal circuit model elements values can be fitted by an expression with the environment parameters, which can improve application scope of the transient thermal circuit model. The experimental results of the simulation show that, after knowing cable type and environment parameters, the transient thermal circuit model elements can be obtained by looking up the table and calculating by expressions, thus enabling fast calculation of the value for the cable core temperature variation while ensuring the accuracy of the results, and can meet the requirements in engineering.

Static tensile mechanical properties and engineering application of constant resistance and large deformation anchor cable

Deep engineering is faced with mechanical phenomena, such as substantial soft rock deformation and in situ stresses, that results in frequent disasters because the energy of the surrounding rock cannot be released normally after excavation. Traditional support materials have low elongation and safety reserves, cannot adapt to large deformations of the surrounding rock, and cannot apply high preload, making it difficult to absorb energy. This study introduces a new type of constant resistance and large deformation (CRLD) cable through static tensile experiments, and compared the results of which with those of ordinary high-strength (HS) cables. Our results showed that the CRLD cable had an obvious constant resistance stage, with a constant resistance value of approximately 415 kN and an elongation rate as high as 25%, which is 3.9 times that of the HS cable. Furthermore, the energy absorption of the CRLD cable was 3.5 times that of the HS cable. Before the first steel strand broke, the temperature of the entire cable was approximately 33 °C, and the energy was absorbed evenly without obvious energy concentration. After breaking, the standard deviation of the segmental elongation of the steel strand was 4.16 mm, with a small degree of dispersion. The deformation of each section of the steel strand was uniform lengthwise and the necking rate of the fracture was 8.5%, indicating that there was no obvious necking. On this basis, a comprehensive mechanical performance evaluation index of the cable, that is, the static toughness UT, was proposed, reflecting the strength, elongation, and energy absorption density of the cable. Compared with the HS cable and another widely used He cable with excellent energy absorption characteristics, the UT of the CRLD cable was 117% higher than that of the HS cable and 38.1% higher than that of the He cable. This study also proposes a support and design principle for the CRLD cable and applies a CRLD cable to a roadway with a buried depth of 1050 m. Our results show that, owing to the high-strength reserve of the CRLD cable, the applicable preload can reach more than 85% of the breaking load of the cable, which is 2.3 times that of the HS cable. After this new support was adopted, the maximum deformation of the surrounding rock of the roadway was 180 mm, which is 36% of that of the traditional support. The deformation of the roadway was controlled and the surrounding rock was stable.

Multi-Parameter Optical Monitoring Solution Applied to Underground Medium-Voltage Electric Power Distribution Networks.

This work presents a multi-parameter optical fiber monitoring solution applied to an underground power distribution network. The monitoring system demonstrated herein uses Fiber Bragg Grating (FBG) sensors to measure multiple parameters, such as the distributed temperature of the power cable, external temperature and current of the transformers, liquid level, and intrusion in the underground manholes. To monitor partial discharges of cable connections, we used sensors that detect radio frequency signals. The system was characterized in the laboratory and tested in underground distribution networks. We present here the technical details of the laboratory characterization, system installation, and the results of 6 months of network monitoring. The data obtained for temperature sensors in the field tests show a thermal behavior depending on the day/night cycle and the season. The temperature levels measured on the conductors indicated that in high-temperature periods, the maximum current specified for the conductor must be reduced, according to the applied Brazilian standards. The other sensors detected other important events in the distribution network. All the sensors demonstrated their functionality and robustness in the distribution network, and the monitored data will allow the electric power system to have a safe operation, with optimized capacity and operating within tolerated electrical and thermal limits.

Online Intelligent Temperature Monitoring System for Tunnel Power Cable Based on Fiber Bragg Grating

To solve the problem that the existing method is better than the power cable and the instability of the environment leads to low accuracy of its monitoring, this paper proposes the research of an online intelligent monitoring system of tunnel power cable temperature based on fiber grating. In the design of system architecture, FACE-TD200, with abundant FPGA programmable logic resources, is used as the main device, and the SuperHawk 1002T fiber grating temperature sensor is set to realize temperature acquisition. In the stage of data acquisition and processing, considering the loss caused by the difference between the wavelength of pump light and Raman scattering light, the spontaneous Raman scattering light power of the acquired signal is calculated. According to a certain energy difference between the upper energy level and the lower energy level of the optical fiber molecule, the temperature information of the cable is calculated. The test results show that the temperature monitoring results of the designed system have a high degree of fitting with the actual temperature values, and the monitoring effect is better than that of the control group.

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.

Load optimization method of cluster power cables based on thermal field simulation and modified particle swarm algorithm

Cluster laying of cables are more and more common in urban transmission and distribution networks. Due to the serious thermal influence between cables, the temperature field distribution of cables laid in clusters is uneven, and the conductor temperature of intermediate cables is higher than that of surrounding cables. To this end, a load optimization method of cable cluster system based on thermal field simulation and improved particle swarm optimization algorithm is proposed in this paper. Based on the finite element calculation of cable temperature field distribution, the method uses the improved particle swarm optimization algorithm to optimize the cable load with the maximum section current carrying capacity as the optimization objective and the conductor temperature of each cable not exceeding 90°C as the constraint condition. The results show that when using the proposed method to optimize the load of 12 circuit, 16 circuit and twenty-four circuit cable groups laid in the pipe, the current carrying capacity of the section is significantly improved, and the rising range increases with the increase of the number of cable circuits, up to nearly 5%; This method can also improve the section load capacity of some lines when the load is fixed. Using this method to optimize the load of cable groups, it can get the optimal scheme of load distribution, improve the current carrying capacity of cable groups and improve the utilization rate of cables.

Experimental study on the fire performance of prestressed steel parallel wire strands

Bridges are critical components of the transportation system and any damage to these structures can result in important social and economic consequences. The literature concerning design standardization for fire hazard in suspension bridges is limited. High strength prestressed steel cables serve as main load-bearing components for suspension bridges, and exposure to high temperatures may result in their prestress loss, leading to structural failure. This paper experimentally investigates the fire performance of 19-parallel wire strands (PWS cables) with a tensile strength of 1860 MPa used as suspender cables in long-span suspension bridges. PWS cables were prestressed and then subjected to UL1709 hydrocarbon fire and simulated open pool tanker fire scenarios in the gas furnace until failure. The load–deflection plots of PWS cables suggest that the cables at ambient temperature sufficiently withstood 95% of their ultimate load capacity. However, the unprotected PWS cables failed within 3–8 min in the fire tests but still sustained the load at 400 °C, which confirms the conservative estimation of 300 °C critical cable temperature mandated by the Post-tensioning Institute. The stress–strain data of tested steel wires correlated well with recently developed high-strength steel wire material models at elevated temperatures. The wire rupture surfaces indicated a brittle failure at ambient temperature and a ductile failure with visible necking under fire conditions. The ultimate (rupture) strain capacity of steel wires decreased from 5% to almost 1% during fire tests. Further, the post-fire strength of PWS cable was unchanged but the elasticity modulus increased by 19% and the rupture strain decreased by 20%. The experimental findings indicate the necessity of fire protection application on PWS cables to keep cable temperatures below the critical temperature of 400 °C in a fire hazard.

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.