Conductor 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.

Overhead conductor heating chamber and temperature effects on the fatigue life of aluminum alloy 6201‐T81 conductors

AbstractThis work investigates the impact of temperature on the fatigue life All Aluminum Alloy Conductors (AAAC) made of 6201‐T81. A heating chamber was developed to simulate thermal effects induced by electric current passage. Wöhler fatigue curves were generated under isothermal conditions at 75 and 150°C and later compared with the one at 20°C. The conductor exhibited similar fatigue life at 20 and 75°C; however, a significant increase of life was observed for tests at 150°C. Hardness tests and failure analysis of wire breakages were carried out on samples extracted from the conductor coil and on artificially aged samples maintained at controlled temperatures. The analyses revealed that at a temperature of 150°C, there is formation of small precipitates of magnesium and silicon within the aluminum matrix, which impeded the propagation of discontinuities, increasing the material's hardness and fatigue resistance.

Analytical solution of conductor tensile force in asymmetrical spans used in overhead power lines and substations with influence of tension insulators

Introduction. Designing electrical substations involves analyzing the horizontal tensile force in flexible tension conductors under varying temperatures. These temperature changes affect the conductor’s length and forces. Problem. Existing methods for calculating horizontal tensile force in conductors often focus on symmetric spans or require complex finite element modeling (FEM), which is impractical for routine substation design. Asymmetric spans with tension insulators present a more complex challenge that current solutions do not adequately address. Purpose. Universal analytical solution and algorithm for calculating the horizontal tensile forces in conductors in asymmetric spans with tension insulators used in power substations or short overhead power line spans. The solution is designed to be easily implementable in software without requiring complex tools or extensive FEM. Methodology. The methodology involves deriving an analytical solution based on the catenary curve formed by the conductor between attachment points at different heights. The analysis includes calculating the conductor’s length for a given tensile force and using a state change equation to determine forces under new temperature conditions. Validation is performed using FEM calculations. Results. The proposed solution was validated against FEM models with varying height differences (5 m and 15 m) and conductor temperatures (–30 °C, –5 °C, +80 °C). The results showed a minimal error (less than 0.15 %) between the analytical solution and FEM results, demonstrating high accuracy. Originality. This paper presents a novel analytical solution to the problem of calculating tensile forces in asymmetric spans with tension insulators. Unlike existing methods, our solution is straightforward and easily implementable in any programming language. Practical value. The solution is practical for routine design tasks in electrical substations or short overhead power lines. Especially in power substations, accurate tensile forces are needed not only for mechanical design and sag calculations but also for calculating the dynamic effects of short-circuit currents. References 23, tables 4, figures 3.

Simulation study on breakdown evolution of tri-post insulator under electric-mechanical-thermal stresses in 1100 kV HVAC-GIL

Due to the presence of electric-mechanical-thermal stress, inner cracks and reduced adhesion strength between metal and epoxy can cause the breakdown of a tri-post insulator in the GIL. In this study, a simulation model was developed to investigate the breakdown evolution of the tri-post insulator subjected to combined electrical, mechanical, and thermal stresses. Various temperature gradients and defect positions were considered, along with the application of an AC voltage of 1100 kV. At room temperature, the tri-post insulator undergoes considerable residual internal stress of up to 35 MPa, primarily concentrated around the conductor and inserts, thereby accelerating the breakdown process. The temperature gradient across the insulator post has a notable impact on breakdown characteristics. Specifically, when the conductor temperature increases from 25 °C to 125 °C, the breakdown time of the insulator with the HV side defect increases by 83.1 %, while the damaged area reduces by 41.9 %. This is attributed to the release of the residual internal stress and the reduction of strain energy. When the defect is located at the GND side, the breakdown channel forms more rapidly, and the impact of temperature gradient on the breakdown process is weakened, because the tensile stress is high but the temperature is low around the GND inserts. The outcomes of this study are hoped to enhance understanding and enable the prediction of insulation breakdown behaviors in practical projects.

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.

Sag and Tension Calculations for High-Voltage Overhead Line Conductors

Overhead lines are used to transmit electricity from where it is generated to the receiving stations. The correct design of an overhead line affects public safety, because it should ensure the required clearances between conductors and the ground and objects located in the space under the overhead line. The temperature of conductors in overhead lines depends on the load current and weather conditions, and affects the sag and tension of the conductors. Calculations of sags and tensions of overhead conductors can be performed using simplified calculation methods that do not consider insulator sets. In some situations, this approach may cause calculation errors. This article discusses algorithms for calculating overhead conductor tensions and sags in the tensioning sections of high-voltage overhead lines, accounting for and excluding insulator sets. The analysis is carried out for different lengths of tensioning sections and various thermal and mechanical states of the conductors.

Finite element analysis of radial temperature of transmission conductor in low-temperature environment

Abstract Most existing studies simplify conductors as isothermal cylinders, neglecting their actual structure and the inter-conductor contacts. This is especially problematic in regions like Northeast and Northwest China, where the conductors face harsh working environments due to significant seasonal temperature variations. Additionally, there is a lack of research under extreme low-temperature conditions. Considering these factors, a temperature field in low-temperature environments was established based on the heat conduction equation. A finite element model and a mathematical model for the transmission conductor were developed using the actual structure of the JL/G1A-240/30 type steel-core aluminum stranded conductor as a reference. Constraint conditions were set, and the model was simulated under various environmental conditions using the finite element ANSYS software. This simulation calculated the radial temperature distribution of the conductors in low-temperature environments, along with the combined effects of transmission line current load, air convection cooling, sunlight intensity, and wind speed on the radial temperature distribution. The results indicate that this method can effectively determine the radial temperature values of transmission conductors under different meteorological conditions, which are significantly influenced by environmental temperature and wind speed. This is beneficial for enhancing the operational safety and stability of transmission lines, achieving dynamic capacity expansion, and improving the transmission capacity of the lines.

Reliability assessment of dynamic line rating methods based on conductor temperature estimation

Dynamic line rating techniques are increasingly prevalent in the computation of ampacity for overhead transmission lines. Some of these methods, commonly employed by system operators, rely on real-time measurements to calculate conductor temperature, either directly or indirectly. Despite their widespread usage, the susceptibility of these techniques to measurement errors has been largely disregarded in prior research. In this regard, this paper includes a groundbreaking reliability analysis addressing the impact of measurement errors on various dynamic line rating techniques in overhead lines, based on conductor temperature estimation. Two case studies are presented, incorporating typical errors from simulations. The first case study adopts a standard 24-hour profile for the variables involved in the conductor ampacity calculation. In the second study, Monte Carlo simulations are conducted, in which meteorological variables are randomly assigned with five load levels to evaluate the current’s influence on measurement noise sensitivity. The resulting ampacity errors across all methods considered are remarkably high, with mean values exceeding 150% in specific scenarios. This unequivocally demonstrates that the commonly accepted levels of measurement accuracy in these widely used rating techniques yield estimations falling far below acceptable reliability standards.

Temperature Fluctuations in Power conductors: Analysis and Overcurrent Relay Adaptation Strategies for Mitigation

In electrical networks, the efficient flow of energy faces constraints primarily associated with the conductor’s temperature. By assessing transmission infrastructure, identifying critical geographical and climatic zones, one can compute the line’s temperature. Focusing on the importance of maintaining optimal conductor temperature for efficient power transmission, this paper evaluates the critical role of conductor temperature in overhead transmission lines and explores its dynamic variations influenced by various ambient conditions. Emphasizing the significance of maintaining optimal conductor temperature, the study delves into mitigation strategies and adaptive protection mechanism, with a focus on overcurrent relays, with specific emphasis on the efficacy of current-time graphs. By addressing these factors, the research aims to enhance the reliability and efficiency of power transmission systems, ensuring sustained performance under diverse environmental scenarios. Overall, the paper contributes valuable insights to optimize the flow of energy in overhead transmission lines, thereby enhance the robustness also, improving the resilience and functionality of electrical networks.

Analyzing the role of emissivity in stranded conductors for overhead power lines

Emissivity and absorptivity are important parameters in overhead power line conductors that depend on the conductor surface condition, so their values change as the conductors age. They have an important effect on their thermal behavior, so it is important to know their value when designing dynamic line rating (DLR) strategies. DLR methods are becoming increasingly important, especially in areas with congested power lines, as they allow the full capacity of the lines to be utilized by dynamically determining their maximum allowable currents without exceeding the safe temperature limits of the conductors, thus ensuring that they operate within safe limits. However, measuring emissivity and absorptivity is non-trivial and requires complex tests that cannot be performed in the field. Using simulations based on a realistic thermoelectric model and experimental tests performed on three types of transmission line conductors in a high-current laboratory, this paper shows the importance and effect of emissivity on conductor temperature. It also presents a method for measuring the emissivity value based on adjusting the emissivity and absorptivity values in the thermoelectric model to match the experimental values. The results presented show that aged conductors allow an increase in the maximum current carrying capacity compared to new conductors in the order of 5–14 %, depending on the conductor type considered and the operating conditions.

Long-Term Ampacity Prediction Method for Cable Intermediate Joints Based on the Prophet Model

The development of power grids is hindered by the limited transmission capacity of cable equipment, necessitating the accurate prediction of dynamic ampacity for cable expansion. This study focuses on the 110 kV cable intermediate joint, employing radial and axial inversion techniques for real-time conductor temperature inversion. Utilizing the Prophet time series model, we predict environmental changes and propose a dynamic ampacity evaluation method for cable intermediate joints. Experimental validation confirms the model’s accuracy, with prediction errors under 10 K, demonstrating its potential for enhancing cable system reliability and power grid development.

Room temperature chirality switching and detection in a helimagnetic MnAu2 thin film

Helimagnetic structures, in which the magnetic moments are spirally ordered, host an internal degree of freedom called chirality corresponding to the handedness of the helix. The chirality seems quite robust against disturbances and is therefore promising for next-generation magnetic memory. While the chirality control was recently achieved by the magnetic field sweep with the application of an electric current at low temperature in a conducting helimagnet, problems such as low working temperature and cumbersome control and detection methods have to be solved in practical applications. Here we show chirality switching by electric current pulses at room temperature in a thin-film MnAu2 helimagnetic conductor. Moreover, we have succeeded in detecting the chirality at zero magnetic fields by means of simple transverse resistance measurement utilizing the spin Berry phase in a bilayer device composed of MnAu2 and a spin Hall material Pt. These results may pave the way to helimagnet-based spintronics.

Thermal model of DC conductors for railway traction networks: A hosting capacity assessment

In this paper, the authors have adapted existing thermal models for the calculation of conductor temperature for use in electrical distribution systems for railway applications in multi-train environments. For this purpose, the authors have used existing standards such as IEEE 738 for overhead lines and have proposed a resolution methodology based on the difference equation model for cables. The authors have opted for a simplified method since the priority in this case is the resolution in systems with multiple stations, lines, and trains. For this same reason, they have chosen to decouple the electrical and thermal calculations so that the electrical variables calculated through load flows constitute the input to the thermal calculation problem. The paper reviews the existing formulation and proposes models for specific use in railway applications in a multi-train environment. A detailed analysis of the results obtained in a real case study is presented as a validation element.

Dynamic line rating for grid transfer capability optimization in Malaysia

<div align="center"><span>This paper details a case study on the implementation of dynamic line rating (DLR) to enhance the ampacity rating of Malaysia’s grid. Utilizing heat balance equations endorsed by the Institute of Electrical and Electronics Engineering (IEEE 738) and the International Council on Large Electric Systems (CIGRE technical brochure 601), the ampacity rating of a Zebra-type aluminum cable steel reinforced (ACSR) conductor on a 275 kV transmission line has been assessed. Real-time weather conditions and conductor temperatures, measured hourly by the DLR sensor over the course of a year, were incorporated into the ampacity calculation to determine the available margin. The weather parameters were analyzed based on the monsoon seasons. A comparative analysis between various methods outlined in the standards and the estimated ampacity rating derived from both standards is presented. According to both standards, the findings indicate that DLR surpasses static line rating (SLR), highlighting the presence of untapped ampacity for grid optimization. Remarkably, CIGRE TB 601 exhibits a higher ampacity rating margin than the IEEE 738 standard, with a percentage difference of 16.20%. The study concludes that the conductor is underutilized and proposes optimization through the integration of real-time weather conditions data into the heat balance equations.</span></div>

Differences using measured and calculated solar radiation in order to estimate the temperature of the conductor in overhead lines

In the last 20 years, installed wind power capacity in North of Spain has grown from 24 to more than 1,650 MW. In this geographical region, wind energy farms are located in places that are far away from the transmission networks so they have to be integrated into distribution networks. Build new overhead lines dedicated for a distribution energy is not the best way to increase the evacuation energy of the wind farms because the cost is quite strong. So, the aim to solve these issues, is by means of an increase in the capacity of existing lines using the dynamic management of the network. This paper is devoted to show the difference of the conductor temperature between the parameter of solar radiation measured by a pyranometer and the use of the theoretical solar radiation which is explained in CIGRE TB601 [1] and IEEE Std. 738-2012 [2] algorithms.

Application Research on Online Power Cable Temperature Detection via Fiber Optics

Abstract Power cable conductor ampacity directly correlates with conductor temperature. Traditional thermocouple measurement fails to ensure real-time monitoring, risking cable operation. Leveraging Raman scattering principles, this study establishes a method for continuous surface temperature detection of long-distance power cables using distributed fiber optics. This approach surpasses OTDR-based measurement in speed and reliability, offering superior online monitoring for cable systems, suitable for widespread adoption.

Capacity Assessment for Wind-Storage Integration System Considering Electro-Thermal Coupling of Overhead Transmission Line

The high uncertainty of wind power generation generally makes the low utilization rate of dedicated overhead transmission lines (OTL) which carry fluctuated power flow transferred from wind farms to main system. Energy storage systems deployed in large scale wind farms to support system power balance creates the opportunities to treat such problem. Therefore, this study proposes an OTL power transfer limit calculation method by solving the electro-thermal coupling equations for dynamic heat exchange process affected by multiple varying ambient conditions. Accordingly, the wind power transmission is optimized and maximized by energy storage operation on the condition that the conductor temperature is maintained under allowable maximum value. Furthermore, the simulation based on proposed method show the coordinated operation of wind farm, related energy storage system and dedicated OTL, which are defined as the wind-storage integration system (WSIS). Finally, case studies demonstrate the effectiveness of the proposed method in analyzing the optimal scales of wind farm and energy storage, with the consideration of dynamic electro-thermal behavior of dedicated transmission line in carrying wind power.

A Three-phase State Estimation Based on Alternating Optimization for Power Systems Including Conductor Temperatures

A Three-phase State Estimation Based on Alternating Optimization for Power Systems Including Conductor Temperatures

Experimental Investigation of the Effect of Conductor Temperature on Corona Performance in Overhead Transmission Lines

Experimental Investigation of the Effect of Conductor Temperature on Corona Performance in Overhead Transmission Lines