High Temperature Superconducting Cable Research Articles

Breakdown Characteristics of Composite Insulation for High Temperature Superconducting Cable

Polypropylene laminated paper (PPLP) and Kraft paper have been studied as multi-layer insulation for high temperature superconducting cable. The experiment was examined with AC and impulse voltages. Short-term and long-term breakdown of insulation samples were investigated. It was found from the experimental results that the breakdown voltage becomes smaller in the order of PPLP, PPLP/Kraft and Kraft, but the lifetime index increases with the presence of Kraft layer in the multi-layer insulation. In addition, the position of PPLP layers has a significant effect on the breakdown voltage of PPLP/Kraft samples under positive impulse voltage. Finally, breakdown mechanism of PPLP/Kraft composite insulation was suggested. Partial discharges in butt-gaps and in the porous structure of insulation layers combined with electric discharges on the surface of these layers are considered to be main factors causing the puncture of multi-layer insulation.

Current Transfer Length and Interfacial Resistance Between Superconductors and Metals in Commercial REBCO Tapes and Cables

High-temperature superconductors (HTSs) are used in a growing number of applications. Technical HTSs usually consist of superconducting and metallic parts. HTS conductors are characterized by their critical current density and critical temperature defined by the superconducting layer, but other quantities such as the current transfer length (CTL) and the interfacial resistance between the superconducting part and surrounding metals are also important characteristics. Since the CTL and the interfacial resistance cannot be measured directly, a method is known to evaluate these parameters indirectly from the characterization of the spatial variation of the surface voltage of the metallic surrounding that is in direct contact with the superconducting material. In this article, we present the details of the experimental method developed to determine the CTL and the interfacial resistance of commercial second-generation HTS conductors of any type of architecture. We apply this method to quantify the interfacial resistance of ten HTS tapes from six major tape manufacturers. Also, since the architecture of a commercial HTS tape is usually more complicated than an “idealized” superposition of two flat layers (i.e., a metallic layer and a superconducting layer), recourse to three-dimensional numerical modeling has been required in order to understand in details the current transfer mechanisms taking place within the tape. We also show that the method can be applied directly to more complicated structures encountered in HTS cables, namely to determine the barrier resistance between a metallic structure in contact with a superconducting tape, providing important information required in numerical modeling when designing superconducting devices.

Transient modeling of quench and recovery of LNG-HTS hybrid energy transmission system based on multi-field coupled analysis

• LNG cold energy is utilized for the operation of HTS cable. • A 1-D model with electromagnetic, thermal and flow analysis is originally proposed. • The complete quench and recovery characteristics can be obtained. • Under a specific condition, the quench of the system can be recovered by itself. • The recovery time has a power law relation with the velocity of liquid nitrogen. In a novel high temperature superconducting (HTS) hybrid energy transmission system, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain very high energy transmission efficiency. The liquid nitrogen (LN 2 ) is used to provide a low temperature environment and can also restrain the quench phenomenon as a protective medium. As the safety of the system is the biggest concern, a one-dimensional model with the quasi static state method is originally proposed in this paper to analyze the quench and recovery behavior. The model firstly introduces the electromagnetic analysis into the thermal and flow analysis, combining intricate interaction of phase change, fluid flow, heat transfer and current sharing. In this paper, the complete quench and recovery characteristics can be obtained when the system is subjected to the default current or thermal disturbance. The results indicate that under a specific condition, the quench of the system can be recovered by itself including different stages, going through the cooling process of film boiling, nucleate boiling, transient boiling and forced convection in turn. The recovery time caused by the default current is much longer than that caused by thermal disturbance and it has a power law relation with the velocity of LN 2 . For the quench process caused by the default current, the maximum temperature of the system decreases with the increase of LN 2 velocity. For the thermal disturbance, the maximum temperature almost keeps constant. The proposed model can predict the quench and recovery behavior in advance, which is significant for the stable operation and design of the hybrid energy transmission system.

Transient analysis of a 22.9 kV/2 kA HTS cable under short circuit using equivalent circuit model considering different fault parameters

The transient behavior of high temperature superconducting (HTS) cables could significantly depends on fault parameters. This paper investigates impact of fault resistance, fault type, and fault duration time on the transient behavior of a 22.9 kV HTS AC cable. To accomplish this, an equivalent circuit model (ECM) is established to model transient and steady state behaviors of understudied cable, while recovery and twisting effects are also considered. Some simulations were conducted using MATLAB/SIMULINK as case studies to analyze the impact of the fault parameters on the transients of HTS cable. The results were shown that fault and grid parameters drastically change the electromagnetic and thermal behaviors of cable, namely, maximum fault current, maximum temperature, and induced Lorentz force. An increase in the fault resistance could significantly reduce the temperature increase and applied Lorentz force. On the other hand, type of fault changes the maximum induced Lorentz force on tapes and change it from kPa to MPa. Also, the effect of fault duration is studied which shows that a drastic increase in the fault time leads to burnout of tapes.

Metal composite T-junction terminals for MW-class aerospace electric power distribution

There is a recent surge in activity to develop high power electric (or hybrid electric) aircraft. Part of this development effort is the creation of lightweight and small volume high-performance motors and airborne power transmission cables. As part of the power transmission of a distributed propulsion aircraft will be T-terminals to extract power to individual motors from a “main” power cable. In this research, a standard pressed plate high purity Cu T-terminal, with cylindrical high-temperature superconducting cables (main cable current of 20 kA, branch cable current of 2.5 kA), were investigated using Multiphysics simulations. Then, a more geometrically optimized high purity Al-Cu composite T-terminal was simulated under similar conditions. Discussed are the influence of T-junction geometry, operating temperature (30 to 50 K), contact resistance, and magnetoresistance on joule losses of terminals with different masses. It is shown the Al-Cu terminal can greatly reduce joule losses/mass of the T-terminal while also having an intrinsic clamping force from thermal expansion of the Al shell of the composite structure.

Parametric study of the hydraulic performance of counter flow LN2 cooled cold dielectric HTS cable

A hydraulic analysis is promising to perceive the complex turbulent flow behavior of sub-cooled liquid nitrogen (LN2) through counter flow cold dielectric high temperature superconducting (HTS) cables. Such counter flow HTS cables comprise of an annular (cryostat) and a central corrugated pipe separated by a HTS conductor layer. Flow of sub-cooled liquid nitrogen through central and annular corrugated pipe affects the hydraulic performance of HTS cable due to the sudden expansion and contraction in the corrugated pipes shape. Therefore, in the present work, the hydraulic performance in terms of friction factor, pressure drop, pumping power and flow pattern of LN2 through central (forward flow) and annular (return flow) corrugated pipe (cryostat) are investigated computationally. Moreover, the effect of various parameters (corrugation pitch and depth) on hydraulic performance is also examined. In order to analyze the effect of corrugation pitches (6, 8, 10 and 12mm) and depths (4, 6 and 8mm), ten different two dimensional (2-D) axisymmetric model of counter cooled HTS cable are developed and solved using computational fluid dynamics (CFD). Additionally, two-equation turbulence model (k-ϵ) is being used to accurately predict the complex flow pattern of LN2 in corrugated pipes. Furthermore, the results of pressure drop are validated with available experimental results. Hence, the hydraulic analysis results are beneficial in opting the corrugated pipes configuration and the allied cryo-units for fluid pumping.

Exergoeconomic Evaluation and Optimization of Reverse Brayton Refrigerator

Abstract In this article, by using exergoeconomic approach, an economic evaluation of reverse Brayton cycle-based refrigerator has been performed for 10 kW range cooling capacity at 65 K. One of the typical application domains of this refrigerator at the considered heat load is cooling of high-temperature superconductor for future power transmission lines that are in the developmental phase in different parts of the world. Multi-objective optimization and sensitivity analysis have been performed to investigate the sources of cost attached to the exergy destruction. Based on exergoeconomic evaluation parameters, recommendations have been provided for deciding the cost-effective design parameters for refrigerators. The significant finding of this analysis is that, for the basic reverse Brayton cryocooler, component performance, the turbine being the major one, needs to be improved to meet the economic criteria of 25 $/W as enumerated in the cryogenic road map for high-temperature superconductor cooling. The exergoeconomic design applied on the reverse Brayton refrigerator for high-temperature superconductor cables cooling can be adapted for other applications such as recondensation and liquefied natural gas cold energy utilization.

Research on Fault Current Endurance Capability of Concentric HTS Cable

Based on the resistance response of high temperature superconducting (HTS) YBCO tape under overcurrent, a physical model of compact three-phase concentric HTS cable under fault current was established using adiabatic approximation. We consider the endurance criteria of no irreversible damage to the superconducting tapes and no significant vaporization of LN2. The fault current endurance capability of concentric HTS cable was obtained at different fault currents. The safety of the superconducting cable can be ensured by adding current limiting device to reduce the fault current magnitude or by improving the relay system to reduce the protection action time.

AC Loss Analysis of 35 kV High Temperature Superconducting Cables

The alternating current (AC) loss is a key consideration of the operation economy and stability of the high temperature superconducting (HTS) cables. In this paper, the sources of the AC loss in the HTS cable are analyzed firstly. The three-phase HTS cable, adopted in the 35 kV km-level HTS cable demonstrating project in Shanghai, China, is modeled by the finite element method (FEM) to calculate the AC loss by the COMSOL Multiphysics. The AC loss of the designed 35 kV HTS cable is 1.31 W/m. The theoretical calculation method is also implemented to verify the modeling results. Furthermore, considering the on-site conditions of the demonstrating project in Shanghai, China, the calorimetric method is conducted by measuring the temperature difference between the inlet and outlet of liquid nitrogen. The obtained results provide useful indications for the future design and research of HTS AC systems.

Efficient Multiphysics Finite Element Simulation of a Transient Fault in a Bi-2223 HTS Power Cable

In this article, the problem of a high temperature superconducting cable (HTSC) response to and recovery from a transient short circuit fault is discussed and a finite element solution to the problem is presented. The full model consists of three subroutines, connecting together: 1) electromagnetic phenomena in HTSCs and associated Joule heat release; 2) heat transfer from the HTSC to the cooling circuit; 3) convective heat transport in liquid nitrogen. These subroutines are connected via geometric and variable couplings. The background of the real cable to be modeled is laid out together with its key properties. The most important parameter and variable calculations are explained in detail. In order to facilitate a computational speedup through manipulation of the active physics during selected intervals of time, the simulation is split in three distinct stages-steady state, transient fault, and recovery. Moreover, it was shown how the entire simulation may be performed over a moderately reasonable amount of time using low computational resources when certain approximations are exploited-namely, using the electromagnetic model only on a limited number of cross sections along the cable. This article shows that fairly accurate results can be achieved on an office PC using a commercial FEM software even without access to computing clusters, and that the same model can be used to examine both normal and transient operation.

Time-Frequency Domain Reflectometry for Live HTS Cable System via Inductive Couplers and Neural Network

High-temperature superconducting (HTS) cable has become one of the most promising technology along with an adaptation of a unique superconducting conductor that allows long-distance transmission of the large volume of electronic power with less power loss. Diagnostic and monitoring technique for the reliable and safe operation of HTS cable system has also become a crucial factor to commercialize the HTS cable system in the regarding field. HTS cable system which needs a cooling process for re-activating superconductors is more affected by the loss of cost and time. This paper is proposing the time-frequency domain reflectometry (TFDR) based diagnostic technique for a live HTS cable system. By adapting inductive couplers, the live HTS cable system and the diagnostic signal would communicate without direct contact. Signal attenuation and distortion during the signal induction are compensated by LSTM-based neural network. The proposed method is applied to an AC 154 kV 600 MVA HTS cable system in and is further verified through Advanced Design System (ADS) software.

Vibration Testing and Evaluation of 35-kV km-Level Domestic Second-Generation High-Temperature Superconducting Power Cable in Shanghai, China

The 35-kV km-level domestic high-temperature superconducting (HTS) power cable project in Shanghai, China, is expected to be deployed in 2021. Facing the complex operating environment in the metropolitan area, such as the vibration excitation from the subway, pile driving, and seismic activities, the vacuum degree, sealability, and insulation performance of the HTS cables may be affected by the unavoidable mechanical perturbations. The response to the potential vibration excitation is a key factor for the safety and stability of the HTS cables in operation. Therefore, this paper conducts a set of vibration testings for the HTS cable under four kinds of vibration conditions, which include the subway vibration, pile-driving vibration, typical earthquake vibration, and Shanghai artificial wave vibration. Results show that the leakage and outgassing rate of the HTS cable is 1.3×10−6 Pa m3/s at a static state, and increases to 1.4×10−6 Pa m3/s after the vibration testing. The HTS cable exhibits insignificant changes after the vibration testings in the dielectric spectrum examination. The HTS cable can keep its function after the vibration testing that possibly occurred in the metropolitan area.

Demonstration of a Triaxial Superconducting Cable in a Private Chemical Plant

A large-scale demonstration test of a triaxial high-temperature superconducting (HTS) cable for a practical cable system was performed in a chemical plant of a private company. The 200 m-long HTS (REBCO: REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> ) triaxial cable, which was manufactured by connecting 3 cables using 2 joints via a snake-shaped layout, was laid approximately 5 m higher than ground level, and the cable was cryocooled by circulating liquid nitrogen. For the preverification test, the rise-up test of the liquid nitrogen and the development of technology for bending the cable, joining it, as well as laying and installing it, were conducted. No leakage of liquid nitrogen at the terminal due to damage caused by heat shock or liquid nitrogen drop impact was observed. The pressure required for the liquid nitrogen to achieve a 5 m height was from 27.5 to 33 kPa, which is in good agreement with the calculated pressure of 33.6 kPa. The cooling rate was well controlled, and the desired level of 4 K/h was achieved. The economic challenges and methods of achieving market penetration were also discussed. The goal was to realize a superconducting cable for practical applications, and it was thought that the energy and costs necessary for cryocooling could be drastically reduced by using the existing cold system in the plant. In this way, it is expected HTS cables can achieve low costs and high energy-saving effects and penetrate markets in the future.

Exergetic analysis of reverse Brayton cryocooler with different turbine arrangements for HTS power cables

The cooling systems of High-Temperature Superconducting (HTS) power transmission cables are unable to achieve the desired performance as prescribed in the cryogenic road map. Reverse Brayton cycle based Cryocooler (RBC) has been identified as a refrigerator that has the potential to achieve the desired performance for higher cooling load demand. In this article, an exergy analysis of the basic Reverse Brayton Cycle (RBC) and its modifications has been investigated for identification of appropriate cycle configuration that will meet the demand for practical applications of HTS cables. The modifications in the basic cycle are carried out with different arrangements of turbines such as parallel or series expansion that may increase the exergy efficiency of the cooling system with a heat load of 10 kW @ 65 K. The analysis is carried out using Aspen HYSYS V8.6, and helium is used as a working fluid. The effects of important process parameters such as pressure ratio, compressor inlet pressure, and flow diversion on the performance are investigated and are used to optimize these cycles. The best cycle configuration based on RBC is identified and recommended based on the results of the analysis.

Characterizations of a Novel Structure of Fault-Tolerant HTS Cable

This paper presents a type of high temperature superconducting (HTS) cable, which is fabricated by winding the second generation (2G) HTS tapes on round former consisting of stranded stainless steel (SS) wires. It has the advantages of strong flexibility, high mechanical strength, and high engineering current density. With taking the resistivity of SS much larger than that of copper or aluminum, the cable has higher resistance and strength than the conventional HTS cable with former made from copper strands at condition of fault accident. After the configuration of the cable is designed in detail, the quenching resistance and fault current limiting are numerically analyzed. We fabricate a model cable and carry out the experiment of fault current. The experimental results show that the quenching resistance of this cable is much higher than the resistance of conventional underground XLPE cable and overhead conductor, which indicates that the proposed cable has a strong ability of fault current limiting and can be applicable in HTS devices with functions of fault current limiting such HTS cable, transformer, motor/generator, and current limiter.

Simulation Analysis of 2D Finite Element Axial Transient Temperature Distribution of HTS Cable

High temperature superconducting (HTS) cables have advantages of low loss and large capacity transmission. In order to analyze and protect the HTS cable, especially in the transient process, this paper develops a new method to analyze its thermal properties. Based on the structure parameters and actual working conditions of three-phase coaxial (tri-axial) HTS cable a two-dimensional (2-D) axisymmetric finite element simulation model along the axis was built in COMSOL. By coupling first and then decoupling, the temperature distribution was studied under the conditions of cooling, rated current, cryogenic system failure, local hot spot and short circuit fault. This method solves the problem that non-isothermal flow (nitf) is hard to converge under transient conditions, and has the advantages of simple and accurate.

Abnormality Monitoring for Three-Phase HTS Cable via Time-Frequency Domain Reflectometry

With the advent of commercialization in high temperature superconducting (HTS) cable systems, maintenance techniques for the HTS cable systems are required. In the HTS cable systems, which must maintain the superconducting state during the operation, real-time monitoring is essential. Therefore, in this paper, a monitoring technique for three-phase HTS cables is proposed. The proposed technique, which is based on time-frequency domain reflectometry, has an efficient instrument configuration compared to conventional techniques. Also, by extracting a feature in the time-frequency domain of the monitoring signals, abnormal phase in a three-phase HTS cable can be identified. The proposed technique is demonstrated by experimental data using a real-world three-phase HTS cable. In order to simulate a local quench in the operation of three-phase HTS cable systems, heating elements are utilized in the experimental setup. It is expected that the proposed technique will improve reliability in operating the three-phase HTS cable systems.

Thermal and Electromagnetic Design of DC HTS Cables for the Future French Railway Network

The use of High Temperature Superconducting (HTS) cables as a technology is considered as key to increasing the power of the electrical grid while reducing the volume of installation. In addition, when transmission currents exceed a few kA, DC HTS cables significantly reduce power losses, rights-of-way and total system mass. This article describes the various studies that need to be carried out in order to correctly size HTS DC cables for the new railway network envisaged by the French company SNCF, which must consider ultra-urban needs. The process used to design DC cables for operating powers of 10, 20 and 30 MW at a nominal voltage of 1.5 kV using commercial (RE)BCO tapes is presented. In this sizing process, the critical current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (B, θ, T) dependence of the superconducting tapes, the thermal properties of the materials and the different cooling modes are taken into account. Several solutions are suggested to ensure that the cable can withstand fault currents and reduce recovery time in the initial state. Finally, with the help of analytical models and industrial data, once the cables have been designed, the various system losses are reported as well as the power or size of the various auxiliary components.

Dielectric Characteristics of Liquid Nitrogen/Synthetic Paper Composite Insulation System for Extra High Voltage HTS Cable

For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper.

Fiber optic quench detection for large-scale HTS magnets demonstrated on VIPER cable during high-fidelity testing at the SULTAN facility

Fiber-optic thermometry has the potential to provide rapid and reliable quench detection for emerging large-scale, high-field superconducting magnets fabricated with high-temperature-superconductor (HTS) cables. Developing non-voltage-based quench detection schemes, such as fiber Bragg grating (FBG) technology, are particularly important for applications such as magnetic fusion devices where a high degree of induced electromagnetic noise impose significant challenges on traditional voltage-based quench detection methods. To this end, two fiber optic quench detection techniques—FBG and ultra-long FBG (ULFBG)—were incorporated into two vacuum pressure impregnated, insulated, partially transposed, extruded, and roll-formed (VIPER) high-current HTS cables and tested in the SULTAN facility, which provides high-fidelity operating conditions to large-scale superconducting magnets. During surface heater induced quench-like events under a variety of operating conditions, FBG and ULFBG demonstrated strong signal-to-noise ratios (SNRs) ranging from 4 to 32 and measured single-digit temperature excursions; both the SNR and temperature sensitivity increase with temperature. Fiber thermal response times ranged between effectively instantaneous to a few seconds depending on the operating temperature. Strain sensitivity dominates the thermal sensitivity in the conditions achievable at SULTAN; however, measurements at higher quench evolution temperatures, coupled to future work to increase the thermal-to-strain signal, show promise for quench detection capability in full-scale magnets where temperature and strain may occur simultaneously. Overall, FBG and ULFBG were proven capable to quickly and reliably detect small temperature disturbances which induced quench initiation events for high current VIPER HTS conductors in realistic operating conditions, motivating further work to develop FBG and ULFGB quench detection systems for full-scale HTS magnets.