High Temperature Superconducting Cable Research Articles

Multi-physics coupling finite element analysis of 10kV tri-axial HTS cable

As an important equipment of power transmission, power cable has been required better performance on cable line loss and current ampacity to achieve its high reliability. This paper proposes an advanced application of superconducting transmission technology in power grid, namely tri-axial high-temperature superconducting (HTS) cable. The corresponding simplified model is established for multi-physical field analysis, and the size of each structure is determined through structural design. The temperature distribution of the cable body is analyzed according to multi-physical field coupling, and the influence of flow rate, size and other factors on the stability of the system is studied. In this paper, it is found that increasing liquid nitrogen volume and flow rate have saturation limit for lowering cable body temperature, and the axial temperature rise rate of cable body tends to be stable when it is greater than 4m. Multi-physical field analysis provides a basis for the design of HTS cable length without having system quench or liquid nitrogen gasification.

Effect of the twisting chirality configuration on the electromechanical behavior of multilayer superconducting tapes

Seeking a geometry that can withstand greater transverse loads based on the electromechanical material properties of high-temperature superconducting (HTS) tape is an effective way of improving the transport performance of HTS cables. The cabling method requires the determination of the optimum twist angle of the HTS tape for withstanding transverse loads. This paper investigates the critical current characteristics of HTS tapes under combined deformation. The limit range of the twist angle under the combined deformation is measured and the optimum twist angle of the HTS tape is determined. The results show that the twisting chirality configuration obviously affects the bending strength of the HTS tape. In the elastic range, increasing the pre-twist angle increases the bending strength of the HTS tape, thereby improving the transport performance. In addition, a numerical model is built to further investigate the effect of the twisting chirality configuration on the electromechanical properties of the HTS tape, and the experimental results are explained. The experimental and simulation results generally agree well, and calculations show that there is always a sharp change in stress at the interface of different materials. These findings explain the mechanism of the effect of the twisting chirality configuration on the mechanical behavior and critical current of the HTS tape. They also provide a reference for cabling methodologies for the HTS cable configuration.

Electrotechnical Features and Theoretical Modelings of the 100-m 22.9-kV/50-MVA BSCCO Cable System

Because of a much higher power density than a conventional underground cable, several high-temperature superconductor cables with different voltages and designs have been developed worldwide and demonstrated in a power grid. The 100-m 22.9-kV/50-MVA BSCCO cable system developed for long-term demonstration has been tested during phase I of three years, after being installed at Gochang Test Yard in Korea first: initial cooling, engineering properties, and its reliability. In this paper, we particularly focused on its dielectric and transport current characteristics investigated under high voltage up to 30 kV or large current, experimentally and theoretically. The results show that the dielectric parameters such as permittivity and loss tangent are similar to a conventional oil filled cable. However, the impedance is one fifth of a concentric neutral cross-linked polyethylene insulated cable with a similar conductor size. In addition, separate estimation of ac loss in the conductor and shield, which has not been clear yet, is also established: the shield's loss is evaluated directly from the shield lead, but the conductor's loss indirectly through the virtual-voltage lead. Then this conductor's loss at the rated current may raise its temperature to a coolant by a few degrees. The lumped circuit model shows that the three-phase shield suggested in our cable system can sufficiently cancel magnetic field generated from any variation of a power load in an actual grid. Finally, the theoretical models based on a home-written code and a commercial package are in good agreement with their corresponding experimental results.

An effective way to reduce AC loss of second-generation high temperature superconductors

Second-generation (2G) high temperature superconducting (HTS) devices have high power density and efficiency for energy applications. However, in alternative current conditions, the vortex movement in 2G HTS leads to energy dissipation at low temperatures, which significantly affects efficiency and adds an extra burden to cooling systems. This energy dissipation is identified as AC loss. Reducing AC loss to improve efficiencies of 2G HTS devices, e.g. HTS machines, cables and fault current limiters, has become a key research focus. We report here on an effective way to reduce AC losses by using a new 2G HTS wire. The principle is to stack narrow 2G HTS tapes into a wire structure, which is called a soldered-stacked-square (3S) wire. Our experiments on solenoid coils have proved that the 3S wire helps to reduce the AC loss by 80%. Moreover, the critical current of the 3S wire can be easily adjusted for various applications. It is envisioned that the 3S wire will become a powerful technology enabling the development of 2G HTS power devices with high efficiency.

Fluid characteristic of liquid nitrogen flowing in HTS cable

For long distance operation of High-temperature superconducting (HTS) cables, evaluations of heat transfer and fluid flow dynamics of liquid nitrogen (LN2) flowing in the HTS cable is important. However, the LN2 flow is complicated when the cable core is housed in a spiral corrugate cryostat-pipe and positioned at an eccentric position to the center of the cryostat-pipe. In this study, the effect of a configuration of a spiral corrugate cryostat-pipe on the pressure drop was evaluated using computer simulation. As a result, it was confirmed that the calculated pressure drop in the spiral corrugate pipe is 17 times larger than that in the straight pipe due to the shrinking and expanding of the LN2 flow at the concave domain. This shrinking and expanding of LN2 flow was assumed to be the flow in a gradual contraction pipe and a gradual expansion pipe respectively, so that the pressure drop was calculated by a theoretical arithmetic analysis. For verification of this calculation, the calculated value was compared with the measured value of a HTS cable system, which was constructed in NEDO project. As a result, these values were agreed well each other and it indicated that the pressure drop in the spiral corrugate pipe could be evaluated by this calculation.

AC Loss in HTS Fusion Cables: Measurements, Modeling, and Scaling Laws

Currently, the use of high-temperature superconducting (HTS) cables in the high-field sections of central solenoid (CS) of DEMO is one of the most appealing applications of the HTS cables in fusion magnets. Due to the pulsed operation of such coils minimization of the ac loss is necessary for the CS conductors. For the stacked-tape HTS cable layout proposed at the Swiss Plasma Center (SPC), the main contributions in the total ac loss-hysteresis loss in stacks, intra- and inter-strand coupling losses-have been studied. The electrical network model is used for the coupling losses, based on which the scaling laws for the ac energy loss are proposed. On the basis of the developed numerical tools, the assessment of the ac loss for the next HTS cable prototypes at SPC is also reported. More than 50% reduction of the total ac loss is expected compared with the first TF cable prototypes tested in the European DIPOle (EDIPO).

Economic Feasibility Study of Using High-Temperature Superconducting Cables in U.K.'s Electrical Distribution Networks

This paper details the key outputs of the U.K.'s first feasibility study of implementing the high-temperature superconducting (HTS) cables in electricity distribution networks to solve capacity issues. This project is mainly aimed at studying the technical and economic aspects of using superconducting cables and comparing them with the existing approaches, to determine whether a demonstration project of the superconducting solution is feasible. The University of Bath in collaboration with Western Power Distribution (WPD) has conducted this study, considering a previous capacity issue in WPD's network using both conventional and superconducting solutions. The first part of the study investigated the different aspects (installation procedures, power capacity, capital, and operational costs, etc.) of superconducting cables, comparing them with conventional cables. This identified the unique benefit of the high power density of HTS cables, which could allow the usage of a low-voltage superconducting cable in place of a high-voltage conventional cable. In the second part of the study, a 132-kV site in WPD's network that required reinforcement has been chosen for performing the feasibility study. As part of this study, a detailed cost benefit analysis (CBA) was conducted, comparing the superconducting solution with the conventional solution. The outputs from the present value analysis that has been carried out as part of the CBA are discussed. The results of the CBA power system studies performed are presented, evaluating the impact that each solution has on the network power flows, losses, and fault levels. Finally, based on the outputs from the CBA and future projections in the costs of superconducting cables, recommendations were made for the usage of superconducting cables in U.K. electricity distribution networks to solve network capacity issues.

Safety Verification of a 275-kV HTS Cable System Under Short-Circuit Current Accidents

A simulation code that analyzes the temperature and pressure in a high-temperature superconducting (HTS) power cable cooled by a forced flow of subcooled liquid nitrogen (LN) has been developed. Analysis of the HTS cable is useful for comprehending the normal operating condition and the generation of heat during the transient state. In Japan, an excessive current of 63 kA may flow in an HTS cable for 0.6 s in the worst case when a short-circuit current accident occurs in a 275-kV class cable. To assess the safety under this condition, a simulation of a 275-kV class 20-m model cable was performed, and the simulation results of the temperature profiles qualitatively agreed with the experimental results. In this study, a finite-difference method was used to solve the nonlinear partial differential equations of the heat-transfer phenomenon through heat conduction. By solving these equations, the temperature profiles of the LN coolant and the cable cores were analyzed. The GASPAK software package (Cryodata) was used to evaluate the fluid properties when the LN temperature in the cable was calculated. According to this result, the simulations focused on the analysis of a real-scale HTS cable in this work.

Cryogenic Electrical Insulation Characteristics of Solid Insulator for the HVDC HTS Cable

A termination in the development of the high temperature superconducting (HTS) cable is very important because it requires thermal insulation as well as electrical insulation. We studied the cryogenic insulation properties of epoxy as a solid insulator for electrical and thermal design of 250 kV class HVdc HTS cable terminations. Electrical characteristics of the epoxy are crucial element in the electrical insulation design of the HVdc HTS cable termination. Therefore, we studied the characteristics of the breakdown and the surface discharge of the epoxy. The results were compared with the characteristics of breakdown and surface discharge of FRP.

Evaporating system for cryogenic support of long length HTS power cables

The paper deals with an analysis of the results of theoretical and experimental research on an evaporating system for cryogenic support as supplied to long length thermostatting channels of high-temperature superconducting (HTS) cables and hybrid power transmission lines as well as thermal control systems for cryogenic components in aircraft fuel tanks during long-term spaceflights. Experimental evidence for nitrogen and hydrogen are presented here. The importance of such research for practical application in developing modern cryostatting systems has been highlighted.The design of an experimental hybrid power transmission line for studying thermostatting of superconducting power cables has been considered in the paper. The transmission line contains three sections with different types of thermal insulation and current leads providing high current supply to superconducting threads with minimum external heat inflow. The unique experimental data on heat inflows from the outer surface of the transmission line in different sections has been obtained by the authors. It is shown that it may be possible to compensate fully for external heat inflow to a cryogenic line as well as to lower the temperature of a cryogenic coolant in the section with an evaporating system for cryogenic support. In order to determine the possible length of the cryostatting work field of a long length superconducting cable, estimates of using liquid nitrogen and liquid hydrogen as a working fluid for various mass flow rates of the coolant feed have been made via the mathematical model describing physical processes in a thermostatting channel using an evaporating system for cryogenic support. Calculation data on changes in the length of the long length temperature cryostat, pressure and cooling capacity of the evaporating cryostat system has been obtained.

Recent Status and Progress on HTS Cables for AC and DC Power Transmission in Korea

The direction of the development of large-scale electric power networks has very much coincided with the history of increasing voltage values ever since the advent of Joule heat loss. However, a high-temperature superconducting (HTS) technology has changed the direction of that history. Furthermore, the HTS technology will rapidly accelerate the speed of such change due to its extremely high current density with no Joule heat loss. For these reasons, many different types of HTS electric power transmission applications have been being discussed, and selected items have been developed. Within a few decades, the technology of HTS ac and dc power transmission applications had already been developed and close to the required level for industrialization. Moreover, some of these applications have been installed, energized, and are operating within real power networks. In this paper, we report on the current status and progress in HTS applications of ac and dc power transmission. In particular, this paper focuses on the application field of superconducting cable among various HTS power applications. In South Korea, the Korea Electric Power Corporation, Naju, aims to introduce more new technologies in order to develop the Korean power network, and it believes that an HTS is a key factor in the development of the next generation of power grid, which will be discussed in detail in this paper.

Powering of an HTS dipole insert-magnet operated standalone in helium gas between 5 and 85 K

This paper describes the standalone magnet cold testing of the high temperature superconducting (HTS) magnet Feather-M2.1-2. This magnet was constructed within the European funded FP7-EUCARD2 collaboration to test a Roebel type HTS cable, and is one of the first high temperature superconducting dipole magnets in the world. The magnet was operated in forced flow helium gas with temperatures ranging between 5 and 85 K. During the tests a magnetic dipole field of 3.1 T was reached inside the aperture at a current of 6.5 kA and a temperature of 5.7 K. These values are in agreement with the self-field critical current of the used SuperOx cable assembled with Sunam tapes (low-performance batch), thereby confirming that no degradation occurred during winding, impregnation, assembly and cool-down of the magnet. The magnet was quenched many tens of times by ramping over the critical current and no degradation nor training was evident. During the tests the voltage over the coil was monitored in the microvolt range. An inductive cancellation wire was used to remove the inductive component, thereby significantly reducing noise levels. Close to the quench current, drift was detected both in temperature and voltage over the coil. This drifting happens in a time scale of minutes and is a clear indication that the magnet has reached its limit. All quenches happened approximately at the same average electric field and thus none of the quenches occurred unexpectedly.

AC Loss Distribution in Two-Layer HTS Cable

We measured the influence of the twist pitch, twist direction, and transport current balance of the inner and outer layers on the ac loss characteristics in a two-layer twisted high temperature superconducting (HTS) cable. To measure the ac loss in each layer, we placed the thermo-couples on each tape face with thermal insulation. In the HTS cable, the inner layer is exposed to a longitudinal magnetic field generated by the twisted outer layer, and the outer layer is exposed to a circumferential direction magnetic field generated by the inner layer. When the inner and outer layers connect in series, the ac loss characteristics in the inner layer exhibit the influence of the outer layer arrangement. When the transport current balance of the inner and outer layer changes, the lowest loss condition exists when the inner transport current exceeds the outer transport current. These phenomena are possible explanations for the amplitude and direction of the magnetic field in each layer.

10 kA Joints for HTS Roebel Cables

Future high temperature superconductor (HTS) high field magnets using multitape HTS cables need 10-kA low-resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide-operating temperature range, from 1.9–85 K. The EuCARD-WP10 Future Magnets collaboration aims at testing HTS-based Roebel cables in an accelerator magnet. Usually, low temperature superconductor (LTS) cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO-coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally, the test results as a function of current and temperature are presented.

Numerical simulation of the electro-thermo-mechanical behaviors of a high-temperature superconducting cable

The performance of a multi-layer composite superconducting tape depends on operating conditions, such as the applied field, temperature and stress. Therefore, accurate analysis of the electromagnetic-thermo-mechanical coupling behaviors of the high-temperature superconducting (HTS) cable is important to understanding the mechanism of interaction among different physical fields and the success of optimizing the design of the HTS cable structure. This paper develops a three-dimensional finite element model based on the twisted-stack slotted-core HTS cable structure for electro-thermo-mechanical analysis. Critical currents of a single multi-layer composite superconducting tape and the whole HTS cable structure are calculated. Profiles of the magnetic field, current density, temperature and stress are also obtained. It is found that the selection of tapes having higher critical current enhances the transport performance of the cable. Current densities are nonuniformly distributed in the stack. From the bottom to the top of the stack, the current density first increases and then decreases, in inverse relation to the magnetic field. Cooling with liquid helium improves the cable transport capacity. The temperature of the superconducting tapes is slightly higher than that of the aluminum core, but the stress in the aluminum core is greater than that in the superconducting tapes. The results imply that the transport capacity of the cable can be improved by selecting superconducting tapes with high critical current density and arranging them in stacks in a manner consistent with the electromagnetic field distribution. The model also explains the mechanism of interaction between different physical fields. It is a useful tool that clarifies the multiphysics coupling behaviors of an HTS cable with complex structure, and provides a theoretical reference for the design of novel HTS cable structures.

Comparison study of cable geometries and superconducting tape layouts for high-temperature superconductor cables

High-temperature superconductor (HTS) rare-earth-barium-copper-oxide (REBCO) tapes are very promising for use in high-current cables. The cable geometry and the layout of the superconducting tapes are directly related to the performance of the HTS cable. In this paper, we use numerical methods to perform a comparison study of multiple-stage twisted stacked-tape cable (TSTC) conductors to find better cable structures that can both improve the critical current and minimize the alternating current (AC) losses of the cable. The sub-cable geometry is designed to have a stair-step shape. Three superconducting tape layouts are chosen and their transport performance and AC losses are evaluated. The magnetic field and current density profiles of the cables are obtained. The results show that arrangement of the superconducting tapes from the interior towards the exterior of the cable based on their critical current values in descending order can enhance the cable’s transport capacity while significantly reducing the AC losses. These results imply that cable transport capacity improvements can be achieved by arranging the superconducting tapes in a manner consistent with the electromagnetic field distribution. Through comparison of the critical currents and AC losses of four types of HTS cables, we determine the best structural choice among these cables.

A Ship Deperming Coil System Using High Temperature Superconducting Cable Technology―Refrigeration―

A Ship Deperming Coil System Using High Temperature Superconducting Cable Technology―Refrigeration―

Effect of Diameter of Nanoparticles on the thermophysical properties of LN2 based Cryocoolants

Nanoparticles have marked the impact both in engineering and biomedical field due to its effective properties that provides better heat transfer rate from the material. Dispersion of nanoparticles in base fluid enhances the thermophysical properties compared to conventional fluids. The following research focuses on the High Temperature Superconducting (HTS) cables, with liquid nitrogen (LN2) cryogen with different nanoparticles and variable diameters, used for power transmission and distribution. Moreover, at operating conditions, heat fluxes are received by HTS cables with different sources such as dielectric losses, AC losses from dielectric material and superconducting tapes during transmission of current that also leads to the increase in operating parameters. In the present research, a feasibility study is done by dispersion of nano particles in LN2 cryogen, at constant pressure and temperature range of 33.9bar and 65-75K with a rise of 1K, for cooling HTS cable. LN2 cryogens is dispersed with CuO, Al2O3 and Fe2O3 nanoparticle by varying volume concentration from 1-5% and diameters of 13nm, 27nm, 29nm, 36nm, 47nm, spherical and cylindrical. Mathematical models developed in the past are used to estimate the thermophysical properties such as density, viscosity, specific heat and thermal conductivity. Fe2O3 Nano particles with 5% volume concentration and13nm diameter provide outstanding thermophysical properties, thus proved to be an efficient coolant in HTS cables.

Development of a lab-scale High-Tc superconducting power cable

High Temperature Superconducting (HTS) cables for power transmission applications are gaining prominence all over the world as the efficiency of power transmission is higher as compared to that of conventional cables. In view of the benefits that can be obtained from usage of HTS cables in future power transmission systems, Applied Superconductivity Laboratory, IIT Kharagpur, in collaboration with Central Power Research Institute (CPRI), Bangalore and Bruker HTS Gmbh, Germany has developed a lab-scale superconducting cable carrying 800 A (DC) current at low voltages. The HTS cable containing 2G YBCO HTS tapes (of width around 4 mm and thickness of 0.1 mm) as current carrying conductors, wound helically around a copper former is tested for superconductivity in an open liquid nitrogen bath-type cryostat using a DC power supply (0–1000 Amps) and necessary measuring instruments (nano voltmeter, temperature monitor etc.) at Corporate R & D, BHEL, Hyderabad. In the present paper, the Voltage-Current characteristic of the HTS cable along with its development procedure is presented.

Turbo-Brayton Refrigerator for High Temperature Superconducting Device

High temperature superconducting (HTS) cable is kept below the material specific critical temperature utilizing sub-cooled liquid nitrogen. Sub-cooled liquid nitrogen to flow in a HTS cable is cooled and circulated by a refrigerator and a pump. The high efficiency refrigerator is important in order to reduce the transmission loss of HTS cable including the power consumption of refrigerator. Then we have developed the high efficiency and reliability refrigerator.We set a goal of developing a refrigerator with a COP of 0.1, a maintenance interval of 30,000 hours and a cooling capacity of 5kW. Our goal was achieved by using the reverse Brayton cycle and turbo-compressor and expander. A year-long performance test had verified that our cooling system of sub-cooled liquid nitrogen using this refrigerator is stable for long operation.