Cable Core Temperature Research Articles

Steady-State Temperature Prediction for Cluster-Laid Tunnel Cables Based on Self-Modeling in Natural Convection

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.

Calculation of cable core temperature and cooling method of submarine cable

Calculation of cable core temperature and cooling method of submarine cable

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.

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.

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.

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.

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.

Optimisation of power cable ampacity in offshore wind farm applications

Inter-array power cables are used to connect wind turbines to the collector and export cable. In the transition from turbine tower to sea, the cable is installed in a J-tube, which has an unfavourable thermal environment and can thus be the thermal bottleneck of the cable installation. To optimize cable installation and reduce CAPEX, improved transient ampacity calculations can be used to determine the dynamic rating. In this work FEM have been applied to calculate the ampacity of a three-core HV cable situated in a J-tube. It was found that by including the trajectory of solar influx, the maximum temperature increased above the admittable cable core temperature compared to the steady-state case. High cable loads will always coincide with wind and thus increased convective heat transfer. By increasing the heat transfer coefficient to a value corresponding to wind speed of 20 m/s at high power production and thus large current, it was found the highest core cable temperature decreased by 18 °C compared to the steady-state case. These more accurate ampacity calculations can be exploited by either increasing the admissible current in the cable by 17% or decreasing the cable cross section.

Mitigation of Magnetic Flux Density of Underground Power Cable and its Conductor Temperature Based on FEM

This article proposes using a metallic plate to be installed above the underground power cable route to mitigate the maximum cable conductor temperature and the ground surface magnetic flux density surrounding the cable route and underground cable derating factor. The article presents a case study containing a single-circuit 145 kV, three-phase individual cables in flat formation. The impacts of the mitigation plate dimensions such as plate width, thickness, the distance between the underground cables and the plate used in the mitigation, and the plate material are investigated. Three kinds of materials are examined in this article, namely aluminum, steel 100, and steel 500. Moreover, the optimal design dimensions of the metallic plate for the case under study were estimated. It is concluded that the shielding factors of the magnetic flux density and cable core temperature with aluminum are greater than steel 100 and steel 500. In addition, the derating factor, which is the ratio of the current capacity of the underground cable with shielding plate and that without shielding plate at the same cable core temperature, is increased to be 1.28 with the use of shielding Aluminum plate, rather than 1.18 and 1.17 in case of using Steel 500 and Steel 100 shielding plates, respectively. Finally, the proposed algorithm was validated by comparing its results with the experimental measurements obtained by the others, indicating good agreements.

Development of Inplantable Surface Acoustic Wave Sensor for High Voltage Cable Core Temperature Monitoring in Intermediate Joint

In this paper, a kind of implantble passive wireless surface acoustic wave (SAW) sensor and its reader are developed to measure the operation temperature of high voltage crossed-linked cable core. A small type SAW temperature sensor is embedded into cable intermediate joint. A radio frequecny transceiver of the reader based on discrete devices is optimally designed to achieve high signal-to-noise ratio and receiving sensitivity. The characteristic of resonant frequency and temperature of SAW sensor is determined by frequency scan method. Through AC withstand voltage and temperature rise test of 110kV cable, it proves that the prototype can accurately measure the operation temperature of 110kV cable core in intermediate joint under high operation temperature and strong electromagnetic environment.

Diagnosis of abnormal temperature rise observed on a 275 kV oil-filled cable surface — A case study

This paper presents a case study on a 275 kV oil-filled cable. The condition assessment and diagnosis are based on analysis of cable surface temperature in relation to its current load and insulation dielectric loss. The work was initiated by a local abnormal temperature rise of 5.2 °C in cable surface temperature, which was observed during a routine inspection. The temperature rise occurred at bend area with a length of approximately one metre in the Blue phase. No PD activity was identified using on-line PD measurement. The relation between cable surface temperature, cable core temperature and cable insulation condition was then simulated based on the thermal model of power cables. According to simulation analysis, poor condition of cable insulation or oil from an oil duct penetrating a region under the cable surface were identified as possible reasons for the problem observed. An in service X-ray scanning technique was employed for further investigation and to aid diagnosis. The X-ray images revealed a slight distortion of the PVC sheath and the presence of multiple voids between cable insulation paper and the lead sheath. It was concluded that an oil leakage from the oil duct to the voids under the cable lead sheath was responsible for the local cable surface temperature rise. The result removed the concern of incipient cable breakdown, and a potential unplanned outage.

Термофлуктуационный метод диагностики состояния изоляционных материалов силовой кабельной линии и прогнозирование их остаточного ресурса

The article is devoted to the investigation of thermal fluctuation processes in insulating materials in accordance with the theory of thermal conductivity for solving problems of diagnostics and forecasting the residual life of insulating materials on the basis of a non-destructive temperature method. Mathematical models are proposed that describe the layer-by-layer temperature distribution of the cable line in accordance with the theory of thermal conductivity using the differential Fourier equation. The analytical dependence of the determination of the temperature of the most heated insulation point (cable core) is refined, its transformation is performed to calculate the cable core temperature taking into account the temperature of the cable surface, the environment, and the vein current for various operating parameters of the power cable line (PCL). The software «System» for measuring and calculating the thermal fluctuation characteristics of SCR (SMaCTC), based on the mathematical model of the temperature field in the cable cross-section, has been developed. The software differs from the existing capability of layer-by-layer control of thermal fluctuation processes based on the temperature value on the cable surface. A comparative analysis of the experimental and calculated characteristics of the temperature distributions has been carried out, and various load modes of operation and functions of changing the cable current have been investigated.

Improved ampacity of buried HVDC cable with high thermal conductivity LDPE/BN insulation

Polyethylene is widely used as insulation in power cables with its excellent electrical properties except its low thermal conductivity. However, insulation-related thermal problems pose a limitation on the ampacity of HVDC cables. Improving the thermal conductivity of insulation may contribute to heat dissipation of cable system and enhance its ampacity. In this work, in order to investigate the effects of improved thermal conductivity of insulation on temperature field and ampacity in a single buried HVDC cable, a numerical simulation model is established by finite element method (FEM) and the cable ampacity is calculated by a modified iteration method. Meanwhile, a range of low-density polyethylene (LDPE) based composites filled with hybrid boron nitride (BN) particles at different loadings are prepared to get reasonable model parameters. Thermal conductivity of various samples is measured and the obtained result shows that the thermal conductivity of BN filled LDPE composite is improved greatly. The simulation results show that the cable core temperature is reduced obviously and the temperature field distribution in insulation becomes more uniform with increasing the thermal conductivity. Besides, the temperature difference between inside and outside of insulation layer shows a decreasing trend at a given load current. Namely, the cable can transmit higher current under the maximum operating temperature due to the improvement of thermal conductivity. All the conclusions imply that the improved thermal conductivity of insulation is of great benefit to the improvement of HVDC cable ampacity.