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Accurate temperature prediction of the operating tunnel cable is crucial for its safe and efficient function. To achieve a rapid and accurate prediction of the steady-state temperature of the tunnel cable, the self-modeling pattern in natural convection on the cable surface in the rectangular tunnel is investigated, and the self-modeling method for the convective heat transfer coefficient calculation is proposed. A thermal circuit model for single cables is further established to predict the cable core temperature, and the model is extended to predict the cluster-laid cable core temperature based on the combined method. The results show that when the tunnel size is neglected, the maximum relative deviation of the convective heat transfer coefficient between the self-modeling method and the finite element simulation is only 1.78% in the studied cases, indicating that the natural convection on the cable surface approximately satisfies the self-modeling method. Additionally, applying the self-modeling method to the thermal circuit can accurately predict the temperature of the single cable core. Furthermore, for the three-phase four-circuit cable, the maximum deviation between the temperature prediction results and the finite element results is within 2 K in the studied cases, which verifies the predictive accuracy of the combined method for the cluster-laid tunnel cable. [ABSTRACT FROM AUTHOR]

Accurate temperature prediction of the operating tunnel cable is crucial for its safe and efficient function. To achieve a rapid and accurate prediction of the steady-state temperature of the tunnel cable, the self-modeling pattern in natural convection on the cable surface in the rectangular tunnel is investigated, and the self-modeling method for the convective heat transfer coefficient calculation is proposed. A thermal circuit model for single cables is further established to predict the cable core temperature, and the model is extended to predict the cluster-laid cable core temperature based on the combined method. The results show that when the tunnel size is neglected, the maximum relative deviation of the convective heat transfer coefficient between the self-modeling method and the finite element simulation is only 1.78% in the studied cases, indicating that the natural convection on the cable surface approximately satisfies the self-modeling method. Additionally, applying the self-modeling method to the thermal circuit can accurately predict the temperature of the single cable core. Furthermore, for the three-phase four-circuit cable, the maximum deviation between the temperature prediction results and the finite element results is within 2 K in the studied cases, which verifies the predictive accuracy of the combined method for the cluster-laid tunnel cable.

In order to indirectly calculate the core temperature of a cable joint, an equivalent transient thermal circuit model of single-core cable joint by considering axial heat dissipation is proposed. Firstly, the temperature field of the middle joint of a 110 kV single-core cable is calculated by finite element method. Based on the heat dissipation path of the core, an improved equivalent thermal circuit model is proposed. The axial heat dissipation of the cable joint core is simplified to a thermal resistance and the temperature rise of the cable body core, the temperature calculation of the cable joint transient process is realized. Compared with the results of finite element simulation, the steady-state temperature errors of the thermal circuit model are within 1 °C, while the maximum temperature errors of the transient process shall not exceed 3 °C, which proves the validity of the model. This method can provide reference for temperature inversion and the dynamic current-carrying capacity prediction of cable joints. [ABSTRACT FROM AUTHOR]

Abstract In order to accurately calculate the relationship between the loading current and temperature rise of DC charging cable of electric vehicles, this article establishes the equivalent thermal circuit model of DC charging cable of electric vehicle based on the thermal circuit model analysis method, and refers to the principle of adaptive filtering, proposes a method to derive the thermal circuit model parameters of DC charging cable of electric vehicle from the actual temperature rise data, and designs a comparison experiments to verify the accuracy of the thermal circuit model of DC charging cable obtained by this method. The experimental results show that the calculation temperature rise and actual temperature rise error of the EV charging cable thermal circuit model obtained by deriving from the actual temperature rise data in this article is small, which verifies that the EV DC charging cable thermal circuit model obtained by this method has a certain accuracy in analyzing the temperature rise of this type of cable. [ABSTRACT FROM AUTHOR]

The demand for electric vehicles has increased over the past few years. Wireless power transfer for electric vehicles provides more flexibility than traditional plug-in charging technology. Charging couplers are critical components in wireless power transfer systems. The thermal effect produced by the magnetic coupler in work will cause the temperature of the device to rise rapidly, affecting the work efficiency, transfer power, operation reliability, and service life. This paper modeled and analyzed each component's temperature distribution characteristics and thermal behavior. Firstly, the magnetic coupler's mutual inductance and magnetic circuit model are established, and the thermal model of the magnetic coupler analyzes the heat generation process. The thermal models of the coupler under three different magnetic core distributions are established, and the temperature rise of each component is obtained. The temperature rise of different parts of the coupler is verified by the temperature rise test structure of the experiment.

In order to improve the utilization rate of cable while ensuring safety and reliability, accurate and rapid evaluation of transient temperature rise of directly buried power cables is useful to improve the management level of dynamic capacity increase and emergency load conditions. Since the existing thermal circuit model is relatively complex or not very accurate, an equivalent three-branch transient thermal circuit model is presented for the complex cable structure and heat dissipation environment based on the uniqueness of the temperature field. Considering the electric circuit similarity, the transient analysis method of the centralized parameter network in the circuit is used to establish the transient adjoint model of the thermal capacity branch, provide the node conduction matrix of the transient thermal circuit model, and write the node temperature rise equation as a function of the node heat flow. By comparing the solution of the thermal circuit model with the finite element results, and the genetic algorithm is used to optimize and obtain the equivalent thermal resistance and thermal capacity parameters of the transient thermal circuit model. The comparison of finite element calculation results proves that the proposed three-branch transient thermal circuit model is more accurate than the two-branch thermal circuit model. Compared to the traditional all-part thermal circuit model, the three-branch model can be rapidly solved and easily applied in engineering.

The progressive trend towards intelligent, eco-friendly, low-carbon, and sustainable development in contemporary industrial logistics parks has catalyzed a substantial influx of new energy power systems. This integration poses unique challenges, including intermittent and fluctuating load characteristics, due to the operation of high-powered machinery such as belt conveyors. Consequently, traditional distribution transformers often face premature failure, attributed primarily to inadequate overload capacity, thereby compromising grid safety. Evaporative cooling technology, as a countermeasure to these thermal constraints, holds the potential to enhance the heat dissipation capacity, thus mitigating overload issues. This study employs a novel methodological blend of thermal circuit parameter analysis and empirical experimentation to comprehensively investigate the performance attributes of evaporative cooling distribution transformers. This study's innovative approach involves the development of a dynamic piecewise thermal circuit model that encapsulates both the natural convection and nucleate boiling heat transfer stages. This model builds on the intrinsic attributes of the pool boiling curve of a lowboiling-point coolant. Critical aspects under scrutiny include thermal circuit parameters, boiling heat transfer correlations, constraints on critical heat flux density, and characteristics of the evaporative coolant. Following the Rohsenow correlation and model experimentation, a suitable boiling heat transfer correlation for the selected evaporative coolant was formulated. The thermal circuit model was then employed to discern the influence of the load coefficient, ambient temperature, and coolant boiling point on the operational behavior of the evaporative cooling transformer. The analysis revealed that evaporative cooling transformers exhibit a commendable aptitude for handling impact, intermittent, and fluctuating loads, demonstrating substantial overload resistance. Hence, they are favorably poised for extensive application in heavy-load industrial logistics parks, especially those harnessing new energy. These findings provide instrumental insights, potentially propelling advancements in the modern industrial logistics landscape. [ABSTRACT FROM AUTHOR]

Time-varying output characteristics of high-power giant magnetostrictive actuators (GMA) are determined by magnetic-thermal-mechanical coupling field effect. However, the influence of non-uniform magnetic field and temperature distribution on the output displacement of GMA is often ignored in the present researches. Therefore, a comprehensive model under multi-physics effects is established in this paper. Firstly, the leakage flux and eddy current effects are taken into account, and the non-uniform magnetic circuit model (MCM) is built. Then, the uneven power losses of heat source in GMA are analyzed according to the MCM results. A three-dimensional time-domain thermal circuit is developed based on the heat transfer equation and the "T" equivalent thermal circuit model. Finally, the time-varying displacement is calculated on the basis of multi-degree-of-freedom dynamics theory, so as to build the entire model. Compared with the traditional lumped parameter model and the steady-state thermal field researches, the proposed model is more accurate in analyzing temperature distribution and output characteristics of GMA under different working conditions. Furthermore, the proposed model can also provide a guidance for the temperature management methods and the optimal designing scheme of GMA in various application scenarios. The accuracy and effectiveness of the proposed model have been verified by experiments. [Display omitted] • A magneto-thermo-mechanical coupling model considering non-uniform flux distribution is built in this paper. • The multi-temperature node thermal circuit could calculate time-varying characteristics of GMA accurately. • Compared with existing literatures, this paper focuses on the time-varying output of the GMA due to temperature rise. • The magnetic field distribution is uneven in GMM, thus affecting the temperature and output characteristics of GMA. • As the temperature increases, the output displacement of the transducer decreases, by more than half at most. [ABSTRACT FROM AUTHOR]

The abnormal increase in the temperature of the cable core is an extremely early phenomenon observed during a mining cable internal-caused fire; therefore, the cable internal-caused fire warning system relies on the prompt and accurate measurement of the cable core temperature. The paper proposed a thermal circuit model to calculate the core temperature from the surface temperature of the outer sheath of the cable. The steady-state thermal circuit model is suitable for calculating the temperature when the cable is working normally and the current is stable, whereas the transient thermal circuit model is suitable for calculating the temperature when the cable is faulty. The calculation error of the model is analyzed through the internal-caused fire experiment of the mine cable, and the feasibility of the model algorithm is verified. The results show that the values obtained using the thermal circuit model are in good agreement with the experimental values, and the relative error is less than 10 %, which can be considered to be the criterion for providing early warning in case of a mining cable internal-caused fire.

A straightforward and fast transient temperature rise calculation model is necessary for electrical engineers to manage power cable load. A self-heating lumped parameter model (LPM) without the requirement of monitoring cable surface temperature is developed to evaluate the real-time transient temperature rise of the power cable in ducts. A mutual-heating lumped parameter model to describe the mutual heat interaction between any two cables is proposed in this paper as well. The transient temperature rise of any power cable in duct is the sum of the self-heating temperature rise and the mutual-heating temperature rise from all the other power cables in ducts. All parameters of these two models are obtained by transient thermal circuit analysis, CYMCAP calculation results and generic algorithm. A case study has been conducted to verify the feasibility of the proposed LPMs and the self and mutual temperature rise for each cable in ducts have been obtained. These results agree with the accurate data obtained from CYMCAP well, indicating that LPM can be used as a fast and straightforward tool to calculate the transient temperature rise of power cables in duct.

Interior permanent-magnet synchronous machines (IPMSMs) have the advantages of high efficiency, high power density and outstanding flux-weakening ability, which make them widely adopted in electric vehicles (EVs). Conventional IPMSMs using rare-earth permanent magnet (PM) materials face the problems of instable price and irreversible demagnetization under extreme operating conditions. To overcome these shortcomings, a V-shape combined pole IPMSM (VCP-IPMSM) is proposed, in which NdFeB PMs at the outer ends of V-shape pole are replaced by ferrite PMs. The improvement of the magnetic-pole scheme on air-gap flux density is analyzed, and the influences of the magnetic-pole geometries on electromagnetic performance are investigated. The thermal circuit model of VCP-IPMSM is established, and the demagnetization characteristics of the machine at different temperatures are analyzed, by which the thermal and demagnetization constraints of magnetic pole are obtained. The genetic algorithm based on response surface models is applied to optimize the magnetic-pole cost and electromagnetic torque simultaneously. Accordingly, with thermal and demagnetization constraints integrated with the optimization method, an optimum scheme is obtained. In comparison with the conventional IPMSM with single-material pole, the proposed VCP-IPMSM is proved to be able to promote the air-gap flux density quality, improve the anti-demagnetization ability at high temperature, and decrease the rare-earth PM consumption with the output torque remaining unchanged.

The oil-immersed transformer is a crucial piece of equipment in the power system. Operating at the specified temperature is necessary to ensure the normal operation of the transformer. The insulation paper on the winding surface has a significant impact on the actual temperature of the transformers, which is often overlooked by researchers. The one-dimensional steady-state heat conduction model of the transformer is established by analyzing the heat diffusion process of winding to transformer oil. Atomic force microscope was used to observe the microsurface structure of insulation paper and copper. According to the experiment, the heat transfer resistance in the series process of heat transfer at 7 0 ∘ C is 0.0138 m2 K/W. Space thermal circuit model of transformer is established by thermoelectricity analogy method, and the simulation circuit is optimized according to the boundary conditions set up in the actual environment. The results show that the error of the hot spot temperature is closer to the measured temperature and decreases by 2.5% when considering the thermal resistance of insulation paper. [ABSTRACT FROM AUTHOR]

• The improved thermal circuit model proposed in this paper exhibits a relative error of approximately 1.5 % compared to the results obtained using the finite element method. In comparison to the IEC thermal circuit model, the maximum discrepancy is 123A, with a maximum relative difference of 12 %. • The variation in seawater temperature, salinity, and pressure adjusts the thermal parameters of seawater, thereby modulating seawater thermal resistance and convective heat transfer coefficient, consequently influencing the current-carrying capacity of the submarine cable. Hence, laid cables are most affected, buried cables in less impact. • Without considering the variability in seawater properties, the calculated current-carrying capacity tends to be higher than the actual values, with a maximum error of approximately 5.5 %. Temperature has the most significant impact, accounting for 3.3 %, while the influences of salinity and pressure are around 1.1 %. The IEC 60287 standard, when calculating the steady-state current-carrying of DC submarine cables, does not take into account the influence of seawater property variations on changing the heat transfer efficiency of seawater, thereby affecting the current-carrying capacity of the cable. resulting in deviations in the calculated ampacity results. This paper considers the influence of seawater heat transfer characteristics on cable heat dissipation efficiency based on heat transfer theory, and Proposes an improved thermal circuit model for submarine DC cables that takes into account variations in seawater properties. Taking the example of a 160 kV submarine XLPE cable, the current-carrying capacity results of the improved model have an error of no more than 1.9 % compared to finite element simulation results. Under identical environmental conditions, the maximum deviation between the improved model and the IEC thermal circuit model is 123A, confirming the necessity of considering variations in seawater properties in the improved thermal circuit model. The seawater property variations studied in this paper include changes in seawater temperature, salinity, and pressure. If the impact of seawater property variations on submarine cable current-carrying capacity is not considered, the obtained current-carrying capacity results are higher, with a maximum error of 5.5 %. Among these variations, temperature has the most significant impact, with an error reaching 3.3 %, while salinity and pressure have relatively smaller impacts, with errors of 1.1 % each. [ABSTRACT FROM AUTHOR]

The operating temperature of the magnetic coupler in wireless power transfer (WPT) systems for electric vehicles (EVs) determines the system reliability and service life. This paper studies the modeling and analysis of temperature characteristics of a general magnetic coupler. Firstly, a thermal circuit model is established to show the heat transfer of the magnetic coupler in the air. Secondly, the heating mechanism of the coil, core and aluminum (Al) shield plate is studied. The thermal power of each component is calculated, and the temperature distribution is qualitatively given based on the proposed thermal circuit model. Then, the temperature distribution of each component is simulated, and the results are consistent with the theoretical analysis. Finally, a 6.6 kW WPT prototype is set up, and the temperature of each component is measured after 30 minutes of operation. The temperature of the coil, 34.6 °C, is the highest among that of the coil, core, Al plate and coil base. The agreement between experimental results and the theoretical simulation results shows that the thermal field simulation can accurately predict the temperature of the magnetic coupler by reasonably setting the thermal power addition method.

Based on the structure analysis and the working principle of cylindrical giant magnetostricve actuator (CGMA) for ball screw preload, a thermal error suppression method using oil cooling system to control the temperature is proposed. Firstly, the heat transfer model and thermal circuit model of CGMA are established; next, the steady-state temperature model and the thermal expansion displacement model of cylindrical giant magnetostrictive material (CGMM) are obtained according to the heat-transfer rules and loop analysis method in circuit analysis; finally, the design parameters of the oil-cooling temperature control system are determined by combining thermal circuit model analysis with finite element simulation analysis. Such optimization method saves a lot of computation and provides a simple way for the design of oil cooling structure. In addition, a test platform for the CGMA is established. The experimental results indicate that the measured temperatures are in good agreement with the simulation results under forced oil cooling, and the relative error is less than 5%, which proves the rationality of the temperature control system. Moreover, the output accuracy and stability of the CGMA is significantly improved with proposed oil cooling method, which further confirms the thermal error suppression method is effective. As a result, this study provides a basis for the application of CGMA in the precise adjustment of double-nut ball screw preload. [ABSTRACT FROM AUTHOR]

To develop a thermal model for air-cooled plate–fin heatsink and evaluate its thermal performance, empirical equations are available to rapidly calculate the pressure drop and heat transfer coefficients for the fins. Besides the heat transfer coefficients, the local air temperature also affects the heat transfer of the fins, which rises along the channel by absorbing the released heat from the fins. In this article, a heatsink model to account for the air temperature rise is proposed, and a thermal circuit model is used to correlate the increased air temperature and the absorbed heat at the fin boundary. With this convective boundary, the temperature distribution for the base plate of the heatsink is calculated by adopting finite-difference method (FDM), which analyzes the conductive heat transfer for the base plate. Both of them have been programed in MATLAB software, and the calculated temperature by the proposed models is compared with the computational fluid dynamics (CFD) simulation. A fan-cooled plate–fin heatsink for a half-bridge power electronics inverter is tested in the laboratory as an example, and the thermal results obtained from the proposed models are within 10% of error with respect to the CFD simulation results and experimental results. The proposed method is also faster than the CFD simulation. The proposed accurate and rapid thermal modeling method will be essential for virtual prototyping and layout/geometry optimization of power electronics systems. [ABSTRACT FROM AUTHOR]

Predictions of physical phenomena in buildings are carried out by using physical models formulated as a mathematical problem and solved by means of numerical methods, aiming at evaluating, for instance, the building thermal or hygrothermal performance by calculating distributions and fluxes of heat and moisture transfer. Therefore, the choice of the numerical method is crucial since it is a compromise among (i) the solution accuracy, (ii) the computational cost to obtain the solution and (iii) the complexity of the method implementation. An efficient numerical method enables to compute an accurate solution with a minimum computational run time (CPU). On that account, this article brings an investigation on the performance of three numerical methods. The first one is the standard and widely used finite-difference approach, while the second one is the so-called RC approach, which is a particular method brought to the building physics area by means of an analogy of electric circuits. The third numerical method is the spectral one, which has been recently proposed to solve nonlinear diffusive problems in building physics. The three methods are evaluated in terms of accuracy on the assessment of the dependent variable (temperature or vapor pressure) or of density of fluxes for three different cases: (i) heat diffusion through a concrete slab, (ii) moisture diffusion through an aerated concrete slab and (iii) heat diffusion using measured temperatures as boundary conditions. Results highlight the spectral approach as the most accurate method. The RC based model with a few number of resistances does not provide accurate results for temperature and vapor pressure distributions neither to flux densities nor conduction loads. [ABSTRACT FROM AUTHOR]

Car charger is the key equipment for the development of electric vehicles. Such equipment is prone to exceed the maximum temperature rising limitation when operating in high temperature environment. Meanwhile, the device temperature of the vehicle equipment is difficult to obtain directly due to the road conditions and other issues, and therefore cannot achieve the temperature protection. In this paper, a smart power adjustment method based on the power device lumped parameter thermal circuit model is proposed aimed at overcoming this problem. In this method, the power device that has the highest temperature inside the charger is analyzed firstly. Then, power device lumped parameter thermal circuit model is established, which is correlated with the ambient temperature and output power. Next, the optimal model parameters can be effectively estimated via the least square method. The experimental results verify that the power control method based on the thermal path model can effectively limit the temperature rising of the charger power device, and improve the thermal stability of the charger.

The conductor temperature of cable in operation is the basis for determining whether the cable reaches the ampacity. For the three core cable, it is difficult to calculate the thermal resistance of the filling layer accurately due to its irregularity shape, resulting in a large error in the temperature calculation of the cable conductor using the thermal circuit model. Therefore, it is proposed to calculate the thermal resistance of the filling layer by temperature field, and then calculate the conductor temperature by thermal circuit model. The conductor temperature of three core cable in steady state and transient state is calculated using the thermal circuit model, and the results are compared with the finite element simulation results. The results show that the maximum temperature difference of the two methods is about 2°C, showing a high accuracy of the proposed method. Finally, the effectiveness of the method is verified by the experimental data, the results show that the relative error between the calculated temperature of cable conductor and the experimental data is within 10%, which meets the needs of engineering application. The research results of this paper contribute to improving the operation and maintenance of three core cables. [ABSTRACT FROM AUTHOR]

The conductor temperature of cable in operation is the basis for determining whether the cable reaches the ampacity. For the three core cable, it is difficult to calculate the thermal resistance of the filling layer accurately due to its irregularity shape, resulting in a large error in the temperature calculation of the cable conductor using the thermal circuit model. Therefore, it is proposed to calculate the thermal resistance of the filling layer by temperature field, and then calculate the conductor temperature by thermal circuit model. The conductor temperature of three core cable in steady state and transient state is calculated using the thermal circuit model, and the results are compared with the finite element simulation results. The results show that the maximum temperature difference of the two methods is about 2°C, showing a high accuracy of the proposed method. Finally, the effectiveness of the method is verified by the experimental data, the results show that the relative error between the calculated temperature of cable conductor and the experimental data is within 10%, which meets the needs of engineering application. The research results of this paper contribute to improving the operation and maintenance of three core cables.

Rapid development of China's economy, changing population structure and reformed economic structure drives rapid growth of energy consumption. As a result, energy safety gradually becomes a hot spot in energy development. Electricity heating technology has been concerned for a long time as a safe and effective mean; as a result, it has developed into a subject integrating electric engineering, pyrology and materials science. A fundamental research is carried out on food heater in this study. First, static electromagnetic induction heating and dynamic electromagnetic induction heating were introduced. To solve reverse problems of temperature rise, thermal power mathematical theoretical model and thermal circuit model of food heater were established based on electromagnetic field and empirical formula. Finally, under certain rotating speed, thermal power in short-circuited winding as well as eddy current thermal power and magnetic hysteresis thermal power in solid iron core was analyzed. [ABSTRACT FROM AUTHOR]

The structure of a thin film confined between two materials widely exists in microelectronic devices. When heat flows across such a thin film, thermal resistance of the film is always coupled with the thermal resistances of the two interfaces. Comparing to numerous studies on the heat transfer across an interface between two dissimilar materials, heat transfer across a thin film and the adjacent interfaces is less investigated, especially when the film has structural or mass disorder. Using molecular dynamics simulations, we systematically investigate the net thermal resistance of two interfaces and the confined thin film, and compare the results with the predictions from the thermal circuit model. When the thickness of a disordered thin film is greater than 2 nm, the net resistance across the film is almost linearly dependent on the film thickness and always larger than the prediction of the thermal circuit model. For extremely small thickness (<2 nm), the amorphous thin film has similar resistance to the crystalline counterpart. The existence of alloy region between two dissimilar materials could reduce the interfacial resistance when the alloy thickness is a few atomic layers, but would enhance the resistance when the alloy thickness is large. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modelling of multi-layered insulated wall assemblies with thermal circuits. [•] Variable concrete and insulation placements and variable concrete density–conductivity variation. [•] Optimal decrement factor and time lag of wall assemblies. [•] Proportional and relative metrics for selecting concrete density. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims at introducing an improved methodology for the dynamic modelling of buildings by the thermal networks method. This methodology employs, as a tool, the commonly used ASHRAE clear sky model to allow for the calculation of the external façade radiation and the distribution of the penetrating solar flux on the internal surface-nodes of the zone. The zone considered has an entirely glazed façade with a varying type of glazing and its enclosure is a rectangle parallelipipedic. The incident solar radiation is determined for building surface azimuths ranging from east to west in 45° step increments. The mathematical formulation of this solar-angle dependent lumped capacitance thermal model is based on the nodal approach and is updated in 15min time increments. The proposed methodology provides more insight to help understand the impact of opaque and glazed façade orientations and layer-formation on energy consumption. Results from annual energy performance calculations vs glazed-façade orientation, for various glazing systems, are given for a building zone location in the Mediterranean region. Depending on the building façade orientation and climatic conditions, proper selection of the type of glazing can reduce the annual building energy consumption. [Copyright &y& Elsevier]