Ampacity Calculation Research Articles

Thermal Analysis of Cable Routes with Joints or Other Discontinuities

The paper addresses rare issue in cable ampacity calculations, namely the presence of discontinuities along the routes. One which occurs in almost all cable installations is the presence of joints. In a standard cable rating analysis, the joints are ignored, mostly because of difficulties in building analytical models that represent the heat transfer phenomena within them. However, they can be a limiting part of the cable rating and, therefore, there is a need to model them correctly. This paper introduces an analytical algorithm for cable rating calculations in the presence of discontinuities with an emphasis on cable joints. New developments are illustrated by several numerical examples.

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.

Investigation of cable current carrying capacity improvement and its effects on transmit power between Egypt and Saudi Arabia project

This paper presents an investigation for current carrying capacity improvement of high voltage cable laid in unfavorable regions crowded with groups of high and extra high voltage power cables. A proposed MATLAB program is developed to predict the ampacity of these cables at 220 kV and 500 kV. The cables are laid in various formats and under various laying conditions. Temperature distribution inside cable layers and through soil layers are studied using a finite element model (FEM) with COMSOL software during full load operation. Calculations are based on Neher-McGrath methods in accordance with IEC 60,287. The results are compared with the manufacturer's technical guarantee. Furthermore, this paper presents a proposed cable ampacity calculation that is applied to determine the ideal cross section area for four circuits of 500 kV underground cables that will serve for future power transmission between Saudi Arabia and Egypt.

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>

Aynı anma gerilimlerine sahip farklı iletkenlerden oluşan yüksek gerilim kabloları üzerine bir araştırma

Aluminum and copper conductors are commonly used in the transport of energy. In this work, high-voltage cables occurring aluminum and copper conductors exposed to the same rated voltage values were analyzed. In order to obtain the same current carrying capacity for copper and aluminum conductors, the relationship between the cross-sections has been determined and then the most appropriate cross-sectional values for each conductor were identified. Three different cross-sectional values have been selected for each conductor type and the calculations for the cables were carried out by using the Cable Ampacity Calculations Program (CYMCAP) within the framework of the International Electrotechnical Commission (IEC) standards. The performance of the cables has been compared in terms of material losses, cable structures and the cable costs. It is seen from the simulation results that aluminum conductor cables have lower cost and higher electrical loses than the copper conductor cables.

Ampacity Calculations of Underground Power Cables With End Effects

Ampacity Calculations of Underground Power Cables With End Effects

New Approach for Ampacity Calculation of Overhead Lines With Steel-Cored Conductors

Due to increasing energy demand and penetration of renewable energy sources into the grid, the transmission system has often been operated closer to its operating limit. This scenario requires the accurate calculation of the lines' ampacity in order to ensure their safe operation and the full use of their capacity. This paper proposes a new approach for calculating the ampacity of overhead lines with steel-cored conductors, using an accurate resistance calculation model in a straightforward way. The alternating current (AC) resistance of this type of conductors can be affected by the core magnetization depending on factors such as the number of aluminum layers and the core magnetic properties, which are properly considered using the proposed model. Results for the conductor AC resistance variation with the carried current value and the ampacity for different scenarios are presented and compared with those obtained using the resistance calculation models proposed in ampacity calculation methods by IEEE and CIGRE´ . Results show that the lines' ampacity tends to be underestimated using the existing models. However, for conductors with one aluminum layer, the IEEE method may overestimate the line's ampacity by considering a constant conductor resistance value, bringing risks of accidents due to conductor overheating.

Prediction interval estimation of dynamic thermal rating considering weather uncertainty

Uncertainty and randomness of weather bring challenges to the accurate estimation of dynamic thermal rating (DTR). To reduce the impact of weather factors on the DTR predictions and to further enhance transmission line ampacity. An ensemble empirical mode decomposition quantile regression temporal convolutional network (EQRTCN)-based interval prediction model is proposed for DTR. Different from the existing DTR techniques, the model overcomes the effects of weather non-smoothness and uncertainty on prediction intervals with low quality by ensemble empirical mode decomposition (EEMD) and quantile regression theory. In this work, a k-means clustering algorithm is first used for the time boundary condition division by considering the coupling between line currents and weather parameters. Then, based on different time boundary conditions, the DTR interval prediction model is proposed by using EEMD, quantile regression theory and temporal convolutional networks. Finally, the proposed improved method for ampacity calculation is incorporated in the EQRTCN to calculate the prediction interval of DTR. The model simulation results demonstrated that the proposed DTR prediction framework effectively reduced the uncertainty introduced by meteorological parameters in interval predictions and provided safe guidance for power dispatch. • Propose a novel EEMD-guided TCN model based on the QR method. • Design a novel time boundary condition division method. • Propose an improved method for line ampacity calculation.

A precise inversion method of cable joint core temperature with non-embedded detection based on UMAP and ISSA-BPNN

Obtaining the core temperature of the cable joint is vital to ensure the safe operation of the modern power system with integration. To improve the speed and accuracy of core temperature inversion, this study proposed a non-embedded cable joint temperature inversion method named uniform manifold approximation and projection (UMAP) and the improved sparrow search algorithm (ISSA) optimized the back propagation neural network (BPNN). Firstly, UMAP is used to reduce the feature dimension of sample data input and enhance the data visualization effect. After dimension reduction, the model input features are consistent with the international ampacity calculation standard, and the calculation speed and accuracy of the model are improved. To improve the optimization ability of SSA, the Tent chaotic operator is introduced, and then the ISSA is used to optimize BPNN to address the issue of unstable output and easy falling into a local minimum. At last, the optimization ability and temperature inversion effect of the improved model were compared with other competing algorithms based on the 10 kV cable joint temperature-rise test and CEC2017 benchmark function. The experimental results show that the proposed method shortens the calculation time of the model, and the mean absolute error of temperature inversion is about 0.1°C. The overall performance is the most outstanding, the training data set is unbiased, and the interpretability of the model improves, which can provide a reliable reference for line operation and maintenance personnel.

Analysis method for the design of long submarine cables

The recent push for renewable electrical energy sources has resulted in a significant increase in the installation of the offshore wind farms. These farms become much bigger than their earlier counterparts and the generated power is much larger. This puts additional performance requirements on the export cables. Long submarine export cables are not only subjected to changing laying conditions along the route, including depth and seabed material variations, but also the loading patterns vary significantly over time. Additionally, applied reactive power compensation measures and the time-dependent grid situation change the distribution of the current along the route. These unique features of long submarine power cables necessitate a new type of approach to their design and construction optimization. This paper introduces a new approach for ampacity calculations of long submarine power cables. As the ampacity calculations form a basis for the design of a cable route, it is of paramount importance that they are performed as accurately as possible. The approach can be applied to general-purpose circuit solvers, and this paper describes how to implement it using the ATP-EMTP software, which is extended to the consideration of concurrent electrical and thermal effects. The approach permits considering all the important local and time-dependent parameters of the analysis simultaneously. In particular, the approach allows simultaneous analysis of the varying laying conditions along the route including changes in the depth of burial and thermal resistivity of the soil together with the temporal variations of the cable loading. Additionally, current characteristics in long AC cable conductors are strongly affected by the reactive power flow, which in turn depends on the location of the reactive power compensation, the reactive power demand for grid operation, and the wind farm voltage reactive power control strategy. Such analysis cannot be performed with any existing analytical tool. Also, numerical tools cannot handle such problems because a 3-dimensional time-dependent analysis of a cable route which is 100 km long would encounter convergence problems as the size of such model would be prohibitive. Hence, at present, the proposed approach is the only one available to solve this complex electro-thermal problem. Several numerical examples illustrate an application of the proposed methodology.

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.

Hybrid Method for Numerical Implementation of Segmented Power Cable Conductors in Finite-element Based Ampacity Calculation

This paper addresses challenges with modelling of segmented power cable conductors using finite element analysis (FEA) for ampacity calculation. Segmented conductors improve current distribution by minimizing skin and proximity effects, thus reducing conductor losses. 2D FEA simulation offers high flexibility and accuracy beyond IEC 60287 for complex laying geometries, but the modelling of losses in segmented constructions using FEA has proven difficult due to the big difference in wire size and twisting pitch, requiring great amounts of computational power. In this paper a hybrid method is proposed, in which the IEC 60287 empirical formulae for segmented conductors are included in a 2D FEA model. The proposed method shows a good correspondence to IEC standard calculations, with deviations in conductor AC resistance of less than 1 %.

A New Method for Analyzing Complex Cable Arrangements

This paper introduces a new analytical method for the analysis of unsymmetrical, three-dimensional cable arrangements thus allowing ampacity calculations for complex underground cable systems. Up to now, the analysis of such systems required application of numerical methods, which require high level of expertise and are generally difficult to use. The resulting computational algorithm is developed from basic principles and is applicable for cables directly buried in a uniform soil. An extension of the method to the situations when the soil drying out occurs in the vicinity of loaded power cables is also presented. The method is illustrated by several numerical examples. Some of them involve crossing of two circuits, which can also be studies using the methods covered in the literature. These examples are used for comparison with the existing standard approach.

Cable Steady-State Ampacity Correction Method based on Multi Physical Field Coupling Algorithm

The difference between the single air laying ampacity test value of medium voltage power cable and the system ampacity of three-phase laying and operation is a common problem in the industry. Based on the TICW-2012 standard, the single cable ampacity of medium voltage single core power cable is tested, and the COMSOL basic simulation model is debugged with the measured ampacity value. On the premise of correct single cable basic simulation model, the system ampacity under three-phase operation under different working conditions is calculated, including triangular laying, plane laying, single circuit and double circuit laying, The difference and correction coefficient between the test current carrying capacity and the of single air laying of medium voltage single core power cable are further analysed. Finally, the analytical formula is derived through the cable ampacity equivalent thermal circuit diagram, and the cable samples are theoretically analysed and calculated. According to the ampacity calculation results of single loop triangular laying and plane laying, the correctness of the simulation results is verified. This study provides a reference basis for the current carrying capacity test and correction of medium voltage power cable in the future, and also provides an effective method for the actual operation state analysis of medium voltage power cable.

Improvement of the Standard Ampacity Calculations for Power Cables Installed in Trefoil Formations in Ventilated Tunnels

Forced ventilated underground installations are challenging to design due to the complex mathematics of turbulent fluid flow. Previous methods have tackled this problem, but only recently, the effect of confinement on a single cable has been considered. In this paper, the effect of cable confinement on the practical case of ventilated trefoil installations is investigated. The complete Computational Fluid Dynamics (CFD) problem is solved using Finite Element Method (FEM) simulations and then validated by laboratory experiments using pipes. FEM simulations are then used to vary the current, the wind velocity, and the distance of the trefoil from the tunnel wall to get a comprehensive picture of the phenomena. This data is used to create a new empirical equation for the Nusselt number for a wide range of operating conditions. The principle of similitude is validated for a scaled-down model of a large tunnel and then used to analyze the thermal rating of tunnels. The new equation improves the IEC standard equations by accounting for the effect of cable confinement on trefoil installations. An important finding of this paper is that a lower maximum permissible current rating is obtained, which if ignored can present a serious risk for thermal damage. It was also found that the cables must be installed three cable diameters away from the wall to prevent the derating effect of confinement.

Improvement and sensitivity analysis of equivalent heat transfer model for dynamic thermal rating of overhead lines

With the rapid growth of power demand, the conductor ampacity calculation method based on the dynamic thermal rating (DTR) becomes more and more important. Based on the shortcomings of the current DTR models, a new DTR model that does not need to measure the wind speed and the operating state of conductor is proposed, which is called the equivalent heat transfer (EHT) model. However, there are still shortcomings in the accuracy of the EHT model in application. In this paper, the EHT model is improved at first according to the consideration of the effect of air physical parameters and the redetermination of the experimental parameters of the EHT equipment. Then, the operation of EHT equipment is simulated through the established experimental platform. The improved EHT model is verified by the IEEE standard. Finally, the sensitivity analysis of the improved EHT model is carried out. The results show that the improved EHT model is greatly improved on application accuracy compared to the original EHT model. Moreover, the improved EHT model can choose the steady-state temperature at any position on the surface of the aluminum ball to calculate the conductor ampacity, and the relative error does not exceed 6%. The improved EHT model is reliable and can meet the safe operation requirements of the power system in practical engineering applications.

Research on Ampacity Calculation and Stress Distribution Characteristics of Overhead Transmission Line

Research on Ampacity Calculation and Stress Distribution Characteristics of Overhead Transmission Line

An Equivalent Heat Transfer Model Instead of Wind Speed Measuring for Dynamic Thermal Rating of Transmission Lines

With the increase in electricity demand, the ampacity calculation based on the dynamic thermal rating (DTR) technology is increasingly significant for assessing and improving the power transfer capacity of the existing overhead conductors. However, the DTR models now available present some inadequacies in measurement techniques related to wind speed. Therefore, it is essential to propose a new model instead of wind speed measuring in DTR technology. In this paper, the influence analysis of various weather parameters on the conductor ampacity is carried out by using the real weather data. Based on the analysis, it is confirmed that the impact of wind speed is significant, especially in the case of the low wind speed. Moreover, an equivalent heat transfer (EHT) model for DTR technology is proposed instead of wind speed measuring. For this EHT model, the calculation of conductor ampacity is realized through investigating the correlation of heat losses between the heating aluminum (Al) ball and conductor. Finally, combined with the finite element method (FEM), the EHT model proposed in this paper is verified by the Institute of Electrical and Electronic Engineers (IEEE) standard. The results indicate that the error of the EHT model is less than 6% when employing the steady thermal behavior of the Al ball to calculate the ampacity. The EHT model is useful in the real-time thermal rating of overhead conductors. It can increase the utilization of overhead conductors while also avoiding the limitation of the existing measurement techniques related to wind speed.

New methodology for design and failure analysis of underground transmission lines

The construction of the transmission lines, in the middle of the cities, are always a big challenge for the designers, industry, government and electric utilities. Components of the project, in the electrical, mechanical and civil works are designed for a high reliability, however, the underground cable design according to international standards have some discrepancies, due to this challenge, a new proposal for the new design and engineering failure analysis. Our findings included a case study of a real underground transmission lines with important contribution with models and mathematical calculation for ampacity calculation as function of depth, temperature, screen connection, materials and thermal analysis for transitory and normal operation of the underground cable in high voltage. This novel proposal generates a recommendation for an update of the international standards IEEE, IEC in the next version.

Calculation and analysis of the steady-state line ampacity weather sensitivity coefficients

The continuous increase in electrical power demand entails the need for larger ratings of overhead lines. For spatial, economic and ecological reasons, contemporary solutions are focused on incrementing the ratings of existing lines. One of these solutions is the real-time determination of line ampacity according to the measured or predicted weather and/or line parameters. The paper is focused on a novel calculation procedure and analysis of the steady-state line ampacity (SSLA) weather sensitivity coefficients (WSCs). The calculation of WSCs is based on the sensitivity analysis of the methodology for the SSLA given in Cigre N° 601 Technical Brochure. On the one hand these WSCs allow a fast estimate of the potential in the introduction of real-time ampacity calculation concept. On the other hand they give a good basis on the requirements for the measurement equipment installed in contemporary dynamical line rating systems (DLRSs). The interrelations between the WSCs and the SSLA are investigated using correlation and regression analysis. Finally, according to the typical design parameters of overhead lines the WSCs and their interrelations with the SSLA are calculated and analysed for typical aluminium steel-reinforced conductors (ACSRs) present in the Croatian transmission system.