Cable Capacity Research Articles

Long-term Thermo-hydraulic Response of the Shallow Subsurface soil in the Vicinity of a Buried Horizontal Heat Source

Heat and mass transfer in the shallow subsurface and in the vicinity of buried heat sources has been often studied based on rather simplifying assumptions, such as the Equilibrium Phase Change (EPC), disregarding film flow, and adsorptive soil-water characteristics. In this study, a fully coupled non-isothermal multiphase flow model is developed that utilizes the Non-equilibrium Phase Change (NEPC) approach. First, the performance of the EPC and NEPC approaches is assessed and validated against the in-field experimental data. The second and main objective of this study is to analyze the thermo-hydraulic response of granular soil close to a buried horizontal heat source (e.g., electrical cables) for one year under real meteorological conditions. Numerical results indicate that the NEPC model has higher robustness in predicting the volumetric water content in the soil close to the soil-atmospheric boundary. However, NEPC and EPC approaches estimate the same temperature variations in the soil. In the case of precipitation (e.g., rainfall), the NEPC model predicts higher degrees of saturation in deeper soil in which the infiltrated water reaches 150 cm below the surface, while, in the EPC model, the infiltrated water barely reaches the 100 cm depth. The increase in moisture content close to the heat source facilitates the heat transfer in the medium and thus results in a 40% to 50% reduction in soil temperature close to the heat source. An accurate prediction of the soil moisture content in the medium is needed to evaluate the performance and thermal capacity of buried electrical cables. Furthermore, the heating/cooling cycles contribute to gradually drying the soil in the vicinity of the heater until the hydraulically equilibrated condition is attained.

A Superconducting Cable With Curved HTS Tapes

Critical current density is an important parameter reflecting power transmission capacity of HTS cable. Based on the superconducting energy pipeline, a tightly wound cable structure along arc of the pipeline is studied in this paper. Critical current density of electromagnetic thermal coupling is calculated and optimized superconducting cable structure is evaluated. Experimental results are useful to the design of high-temperature superconducting (HTS) cable in energy pipelines.

Effect of Pitch Angle on the Winding Capacity of Nb3Sn Rutherford Cable

Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Rutherford cable can be used in the next generation of superconducting magnets above 10 T which cannot be reached with NbTi strands. Rutherford cable is a multi-strand twisted cable with a two-layer structure and rectangle or trapezoidal cross section. Strands are fully transposed with respect to magnetic field. The pitch angle is important for Rutherford cable, which affects the AC loss and bending ability of the cable. Usually different magnets adopt different pitch angles according to the requirement. The winding capacity of the cable is one of a key point. To evaluate the influence of the pitch angle on the cable winding capacity and establish a reference for a new cable design, finite element method based on ABAQUS has been conducted to simulate the cable winding process.

Failure prediction method of the anchor cables in the metro stations under unilateral deep excavation

To ascertain the anchor cable failure caused by the overturning and slipping of the station structure under unilateral excavation with zero distance from the station, this study takes the balance of the station-cable system under zero-distance unilateral excavation as the research object, and derives the total anti-slip force and anti-overturning moment of the cables based on the Rankine’s earth pressure theory and the force balance of the metro station. In addition, a novel failure prediction method is proposed to judge the failure of the station-cable system under various design conditions by taking the supporting capacity of the multi-layer cables as the evaluation index and multiple main influencing factors as the control indexes, so as to predict the structural risk. This method comprehensively considers multiple independent variables such as excavation depth, groundwater level, interval spacing and anchor cable design angle. Furthermore, based on Pearson correlation analysis, the sensitivity of the cable supporting force to various factors decreases in the following order: excavation depth > groundwater level > interval spacing > station width > cable design angle. Therefore, reducing the excavation depth is the most effective way to reduce the risk of the station-cable system caused by unilateral excavation. If it is necessary to increase the excavation depth, the cover-excavation reverse method can be used to indirectly reduce the effective excavation depth, thereby ensuring the safety of the structural system. This method can predict the risks of similar projects and reduce the occurrence of accidents.

Optimization and Cold Test of a Triaxial 2G HTS Power Cable With High Current Capacity

Triaxial HTS AC power cables, that incorporates three HTS phases wound around a single core within a single cable is considering the optimal solution for low and medium voltages. Such a design permits to save expensive HTS conductor and to increase the power density transmitted. It is difficult to increase the transmission capacity of a triaxial cable by increasing its operating voltage and therefore, insulation thickness between phases. The other way is to increase the operation current by using a multilayer structure in each phase of the triaxial cable. This task demands a complicated optimization analysis and a precise manufacturing technology. Following our previous studies, we developed and tested the triaxial cable prototype with two layers per phase made of ReBCO wire. The optimal parameters of the cable (twist pitch, diameters of phases, etc.) have been determined using the numerical simulation methods developed. DC and AC tests of the cable has been performed. In the result, the feasibility to provide a uniform current distribution in a triaxial cable, each phase of which consists of two layers, has been demonstrated. With the outer diameter of ∼24 mm only, this is the most compact triaxial HTS power cable manufactured and tested up to date with currents up to 4 kA per phase. The anticipated power transfer with three phases of this cable can be as large as ∼34 MW.

Low frequency AC transmission systems for offshore wind power plants: Design, optimization and comparison to high voltage AC and high voltage DC

Low frequency AC technology has been presented as a configuration that can potentially reduce the total cost of existing transmission systems. Such cost reduction could be achieved by increasing the power transfer capacity of High Voltage AC cables operating at low frequency and removing the offshore converter when compared to High Voltage DC systems. The purpose of this paper is to suggest an optimal design of Low Frequency AC transmission systems. This results in obtaining the optimal Low Frequency AC voltage level, location, number of reactors and the Back-to-Back converter size for an Offshore Wind Power Plants with a defined rated power and distance to shore. Additionally, the Low Frequency AC, High Voltage AC and High Voltage DC equivalent configurations are compared in terms of total cost and the final transmission system is selected. The analysis of a practical case study is presented in detail, followed by an expansion of the methodology application on various configurations. Also, cost sensitivity analyses for two opposed cases are provided to identify the variation of the break-even distance of Low Frequency AC with High Voltage AC and High Voltage DC. Lastly, different non-standard transmission frequencies are analyzed and an optimal frequency is defined for a range of Offshore Wind Power Plants rated powers and distances. The paper presents a methodology that can be applied considering different relevant parameters, e.g. transmission voltages, cable cross sections and cost data. Based on parameters available in the literature, the study results show that Low Frequency AC is not currently viable.

Study on electromagnetic-fluid-temperature multiphysics field coupling model for drum of mine cable winding truck

Aiming at solving problems of low efficiency, low cable capacity in current 300m open-pit mine cable winding truck, a 900 m cable winding plan was proposed. In this paper, the mechanism of the thermal effect of the cable was described, and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system. Considering the structure of the drum, the number of cable winding layers, the factors of heat conduction, heat radiation and convective heat transfer in the actual working process, the steady state analysis of the multi-physical field coupling was carried out. The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field, which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding, as well as the temperature distribution and heat dissipation characteristics of different structures of the drum. The results show that three layers of cable winding is the best design. The lowest temperature of closed cylindrical drum is 70°C after heat dissipation, which has obvious advantages compared with the lowest temperature of 85° after heat dissipation of squirrel-cage cylindrical drum. The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.

FRP Cables to Prestress RC Beams: State of the Art vs. a Split Wedge Anchorage System

Versatility and high performance in terms of specific stiffness and strength, as well as non-corrosive sensitivity, make FRP (Fiber-Reinforced Polymer) cables a viable alternative to steel ones in the development of prestressing systems. On the other hand, the orthotropic and brittle nature of FRPs could trigger a premature failure of the cable in the anchorage system, for which several solutions have been proposed so far in civil structural applications. In this context, after a preliminary state of the art, the work introduces a split wedge anchorage for FRP (ϕ = 12 mm) cables proposing two different solutions for steel wedges having the external surface: either (1) a constant (3 degrees) slope or (2) a double slope obtained by shaping it with an angle of 3.0 degrees before and then of 3.1 degrees along the most tapered part. The goal was to exploit the nominal cable capacity (257 kN), avoiding stress peaks that cause its premature failure. The proposed solutions have been experimentally tested and, as far as the double angle solution is concerned, the failure loads were equal to 222 and 257 kN, denoting that the proposed solution can reach the cable capacity. Clearly, further investigations are needed to check the variability of the results and eventually improve the system.

Feasibility study for online assessment on fatigue failure of aluminum cable steel reinforced conductors based on DC resistance measurement method

AbstractThe strength of aluminum cable steel reinforced (ACSR) is an important index of loading capacity and safety of cables and will decrease with fatigue damage. However, the strength of ACSR used in transmission lines would be difficultly measured online. Hence the objective of this work is to investigate online measurement parameters employed to characterize fatigue damage of transmission lines. The resistance and strength characteristics of ACSR conductors in long‐term service were experimental studied; it revealed that strength loss rate is positively correlated with DC resistance growth rate. Then the DC resistance growth rate may be used as a fatigue damage evaluation index. Although the DC resistance of transmission lines is difficultly measured online, a resistance and inductance (RL) distributed parameter model simplified and an online measurement scheme were proposed. The simulation and experimental results showed that the DC resistance can be effectively and accurately measured online.

Enhancing the self‐resilience of high‐ renewable energy sources, interconnected islanding areas through innovative energy production, storage, and management technologies: Grid simulations and energy assessment

Electrification of heating and transportation can be greatly combined with excess energy production from variable renewable energy sources that exist in many geographical islands. Grid interconnections, where available, play a vital role in the energy system as provide the required balance between energy consumption and demand but many limitations emerge due to cable capacity and other technical constraints, which in many cases, lead to curtailment events. With the minimization of the energy exchange through the cable between islands and the mainland, the islands' self-resilience is enhanced. The islands of Samsø and Orkney are used as the case studies where, among others, the specific technical solutions of (a) heat pump districting heating with heat storage, (b) electrolyzer for hydrogen production, and (c) electrical vehicles are examined. The proposed technical solutions are enhanced by Demand Side Management actions utilizing high renewable energy sources availability and curtailment events. The solutions are examined and compared with a reference/current status scenario for each island. This work is based on a detailed model representation, using Modelica language, of the transfer and distribution grid assets, allowing the estimation of the impact of the proposed electrification solutions to the grid level as well as the island level. Simulation results revealed that with the proposed actions in Orkney, annual energy export is reduced by 24 GWh but the corresponding energy imports are slightly increased by 13 GWh, reducing curtailment by 1.4 GWh (77%). As for Samsø, the energy imports are reduced by 5 GWh, while the energy imports increase by 2.0 GWh. Grid losses remain at the same level as before at around 2%, but some distribution lines have significantly lower energy traffic due to higher renewables self-consumption.

Electromagnetic Analysis of HTS DC Cables Based on Critical State Model

High-temperature superconducting (HTS) DC cables have the advantages of low transmission loss, high current density and large transmission capacity, which have gained more and more attentions in recent years. The typical structures of HTS DC cables include unipolar and bipolar coaxial that doubles the cable's transmission capacity. Based on the critical state model, this article analyses and contrasts the critical current density distributions and degradations due to magnetic field in the HTS tapes of the unipolar and coaxial bipolar DC cables. The influences of the bipolar cables with different voltage levels are also compared. The results show that the critical current density degradations due to magnetic field are almost the same in both unipolar and coaxial bipolar structures, which are mainly caused by the self-field. For the bipolar cables, the current density distribution in the outer layer HTS tapes changes with the voltage level. To evaluate the influence of the axial magnetic field, a 3-D model of the unipolar cable is established with a helical wound pitch of the HTS tapes. The results show that the axial magnetic field is relatively low and the critical current density would not degrade if the helical angle of the HTS tapes is reasonably small.

Pooling the cable: A techno-economic feasibility study of integrating offshore floating photovoltaic solar technology within an offshore wind park

In this paper, a techno-economic analysis is performed to assess the feasibility of adding an offshore floating solar farm to an existing Dutch offshore wind farm in the North Sea, under the constraint of a certain fixed cable capacity. The specific capacity of the cable that connects the offshore park to the onshore grid is not fully used due to the limited capacity factor of the wind farm. The principle of cable pooling allows to add floating solar capacity. Using weather data it is found that adding solar capacity leads to forced curtailment due to the cable capacity, but this is quite limited as result of the anti-correlation of the solar and wind resource. For the economic analysis, different scenarios regarding subsidy measures are considered for the calculation of net present value and levelized cost of electricity. Also the optimum additional PV capacity for each scenario is computed. The results show that with higher cost per Wp, optimum PV capacity decreases, but more favourable subsidies lead to higher optimized PV capacities. As the aim of the paper is not limited to a case study a methodology is developed for generalization of the techno-economic analysis of a hybrid solar/wind park. In this generalization, the initial investment, system degradation, cable capacity, number of hours when each system is active, and energy price, are implemented to compute the optimum PV capacity regarding the net present value as an indicator for economic analysis of the project.

Thermal Effect of Single Loop Shield on High-Voltage Cable Line Capacity

The paper deals with a single-loop shield with an asymmetric magnetic coupling used for a magnetic field mitigation of a high-voltage three-phase cable line. The goal is to evaluate a thermal effect of this shield on a cable line capacity. To calculate the flat cable line capacity in the nonshielded case, we use a standard IEC 60287. To achieve the goal we carry out a numerical simulation of the thermal field when the shield is installed. Wherein, we deal with two specific sections. One is a long section with the shield being distant from the cable line. The other is a relatively short section where the shield is located near the power cables. The thermal field is applied for a long section in a two-dimensional formulation, and a three-dimensional formulation is used for the short section. Hence, we have obtained the dependences of the maximum temperature of the power cables on parameters of the shield and its location height above the cable line. The most significant allowable cross-sections of the shield cable and their location height have been determined, when the thermal effect of the shield does not decrease the cable line capacity. These results have ensured the maximum cable line capacity while shielding. The shield temperature is shown to exceed the allowable level in the short section. To reduce it the thermal backfill has been used. We recommend the values of its thermal resistivity to be used for different parameters of the single-loop shield.

Grid Island Energy Transition Scenarios Assessment Through Network Reliability and Power Flow Analysis

This paper presents a methodology for the reliability and power flow analysis of islands or off-grid power networks for situations of scarce data and information. It offers a new and pragmatic approach to derive the required power network information, including the power cable parameters and the load at each power node. The paper aims to present the developed methodology, and to illustrate its application, using Ushant Island as a case study. The assessment of the current power network status and the reliability analysis are presented. Grid performance parameters are further compared for conventional diesel generator operation and renewable energy generation scenarios, demonstrating the advantages of replacing the existing diesel units with renewable energy sources in terms of system reliability. The analysis shows that by introducing renewable energy systems to the island’s grid, the reliability of the grid increases by up to 50% and cable capacity usage reduces by up to 30%. Furthermore, this work suggests that it would not be necessary to modify the grid cables when substituting the diesel generator. The paper will be of interest to network planners, community stakeholders, project developers and decision-makers concerned with renewable energy investment on islands and in remote rural areas.

Heat Storage of Paraffin-Based Composite Phase Change Materials and Their Temperature Regulation of Underground Power Cable Systems.

Excessive heat accumulation in backfill materials causes thermal fatigue damage in underground power cable systems that significantly affects the cable carrying capacity. To improve the thermal conditions of the system, two types of composite phase change materials (CPCMs) were prepared by incorporating paraffin into porous ceramsite (CS)/expanded graphite (EG) in this study. EG and CS can carry 90 and 40 wt.% paraffin, respectively. The phase change temperature of paraffin/CS and paraffin/EG CPCMs was approximately 65 °C, and the corresponding latent heats were 63.38 J/g and 156.4 J/g, respectively. Furthermore, the temperature regulation by CPCMs was evaluated experimentally by designing a setup to simulate the underground power cable system. The reduction in the maximum temperature of the backfill materials with paraffin/CS CPCM and paraffin/EG CPCM was approximately 7.1 °C and 17.1 °C, respectively, compared to reference samples. A similar conclusion was drawn from the heat flux curves. Therefore, the prepared CPCMs could significantly alleviate temperature fluctuations, where the paraffin/EG CPCM provided better temperature regulation than paraffin/CS CPCM. Both materials have potential applications for use in backfill materials for underground power cable systems.

Repeater Power Conversion Efficiency in Submarine Optical Communication Systems

In power-limited trans-oceanic submarine systems, the electrical-to-optical (E/O) power conversion efficiency determines the amount of optical signal power generated by repeaters, which governs the cable capacity. In contrast to conventional submarine systems, recent single mode fiber spatial division multiplexing (SDM) systems operate at a lower channel power and support a larger number of optical fibers. Moreover, pump sharing technology is used in SDM systems to enhance cable capacity and system reliability, where a group of pump lasers are combined to feed a group of fiber pairs. The repeater E/O power conversion efficiency is directly related with cable capacity, as well as capacity per power and cost per capacity analysis. Therefore, it is important to understand the characteristics of repeater E/O efficiency. We developed a model to analyze the repeater E/O efficiency in submarine SDM systems. Experimental measurement data of pump lasers and numerical simulation results of Erbium doped fiber amplifiers (EDFAs) were used as input information to the model to analyze repeater E/O efficiency in various system designs. Based on the E/O efficiency model results, we investigated cable capacity using the Gaussian noise (GN) model. Moreover, cable capacity per power was calculated and compared based on three different power metrics: (i) electrical supply power, (ii) pump optical power and (iii) EDFA output power. With the aid of the repeater E/O efficiency model, one can analyze the efficiency of submarine systems using the direct metric of cable capacity per electrical supply power.

Study on Reactive Power Compensation Strategies for Long Distance Submarine Cables Considering Electrothermal Coordination

Long-distance high voltage alternating current (AC) submarine cables are widely used to connect offshore wind farms and land power grids. However, the transmission capacity of the submarine cable is limited by the capacitive charging current. This paper analyzes the impacts of reactive power compensation in different positions on the current distribution on long-distance submarine cable transmission lines, and tests the rationality of the existing reactive power compensation schemes based on electrothermal coordination (ETC). Research shows that compensation at the sending end has obvious impacts on current distribution along the cable, and the maximum current occurs at the sending or receiving end. Moreover, the reactive power compensation at sending end will reduce the current at receiving end of the line. On the contrary, it will increase the current at sending end. Compared with the directly buried laying method of the submarine cable in the landing section, the cable trench laying method can increase the cable ampacity of the landing section and reduce the reactive power compensation capacity at the sending end. The ampacity is the current representation of the thermal limits of the cable. ETC exploits the cable ampacity to coordinate current distribution on transmission lines under existing reactive power compensation schemes, thus optimizing the reactive power compensation schemes and avoiding the bottleneck point of cable ampacity.

Modeling and Experimental Measurement of Power Efficiency for Power-Limited SDM Submarine Transmission Systems

Power efficiency of long-haul optical fiber transmission has emerged as a critical challenge to cost-effectively increasing submarine cable capacity. Building on previous experimental work and informed by physical system modeling and optimization, we report on extensive amplified transmission experiments characterizing the metric of fiber capacity per unit pump power over a range of amplifier powers and link distances relevant to power-limited spatial-division-multiplexed submarine systems. We compare experimental results with modeling incorporating optical amplifier physics as well as generalized droop, demonstrating excellent agreement over the range of powers and distances tested. We predict the performance gains achievable by further optimizing the system design and implementation within tolerances ideally achieved in deployed submarine systems, and estimate fiber pair counts and total cable capacities achievable for the link distances investigated. Our results suggest the utility of amplifier pump powers as low as 20 mW and output powers as low as 6.5 dBm in reaching Pb/s cable capacities.

Design, Acceptance and Capacity of Subsea Open Cables

This article will discuss the collaboratively formed cross-industry open cables concept for characterizing optical performance of undersea cables with the intent of assessing and understanding their capacity potential. The article proposes definitions of two critical nonlinear and linear performance metrics for open cables: GSNR (Gaussian or generalized signal to noise ratio) and SNR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ASE</sub> (Signal to noise ratio amplified spontaneous emission), including effects such as GAWBS (guided acoustic wave Brillouin scattering) and signal droop. Measurement methodologies for these metrics are proposed, with considerations for limitations and impact of the test conditions and characteristics of the transponders used. Expanded definitions are offered to enable variable symbol rate transponders to be used for measurement, with considerations for scaling of SNR values. Considerations for using these metrics for capacity assessment and applying these techniques to concatenated multi-segment systems are introduced. Recommendations on key parameters for system specification, system characterization, and proposals for SNR-based performance budgeting tables are also discussed as foundational elements to enabling accurate estimation of the capacity potential of a subsea open cable.

Analysis of Current Carrying Capacity of Power Cable Based on DTS

This article uses a distributed optical fiber temperature measurement system (DTS, Distributed Temperature Sensing) to fix the temperature measurement optical fiber on the surface of the power cable, collect the real-time operating temperature of the power cable, conduct the ampacity test, and analyze the cable laying method and depth, soil temperature, Soil thermal resistance coefficient, cable spacing and irradiation strength and other test conditions, the impact on the current carrying capacity of power cables. According to the real-time monitoring temperature of the cable, the alarm can be made when the cable temperature is too high or the temperature rise speed is too fast. And on the basis of determining the working temperature and load operating conditions of the cable conductor core, dynamically calculate the current carrying capacity of the cable, which is conducive to improving the performance of the power cable and increasing the load capacity of the power cable.