High Temperature Superconducting Cable Research Articles

Condition Monitoring of 154 kV HTS Cable Systems via Temporal Sliding LSTM Networks

High-temperature superconducting (HTS) cables are expected to be installed in cable tunnels that are already constructed in urban districts. Therefore, the installation of normal joint boxes is inevitable, and it is necessary to develop a diagnostic methodology that considers both the existence of the joints and the electrical characteristics of HTS cables. In this work, temporal sliding long short-term memory (TS-LSTM) is proposed to estimate the locations of the joints that can be hidden by multiple reflections. TS-LSTM includes short-term TS-LSTM and long-term TS-LSTM for analyzing various time dependencies. The reflected signals of the actual joints, which are distinguished from multiple reflections, are analyzed via the chirplet transform (CT) which is one of the time-frequency (TF) analysis methods. The proposed condition monitoring method is applied to an AC 154 kV 600 MVA HTS cable system (1 km) connected to a real power grid network in Jeju, South Korea. For the validation of the proposed methodology, the dielectric and electrical characteristics of the 154 kV HTS cable system are monitored during the cooling process.

Analysis application possibilities of high-temperature superconductors in electric networks

In the article the technical analysis of existing constructive decisions concerning use of high-temperature superconducting cables is carried out. The features of the use of superconductors in electrical distribution networks are analyzed. The advantages of using high-temperature superconductors in comparison with low-temperature superconductors are established. It is determined that the use of high-temperature superconductors, due to the increased critical parameters, provides an increase in the power of transmission lines and energy saving. From the analysis it follows that high-temperature superconductor wires of 2G generation have better operational characteristics, respectively, their use is more efficient compared to wires of 1G generation. A scheme of a three-phase high-temperature superconducting power transmission network with a neutral wire is considered. The working conditions of a three-phase power network with high-temperature superconducting cables are analyzed. It is determined that the use of two cores of a high-temperature superconducting cable of a distributed power transmission system provides an increase in the throughput of electric power in distribution electric networks. Accordingly, the efficiency of electric power transmission is increased, as well as the loss of AC power and operating costs are reduced. It is shown that the use of the reactor reduces the requirements for protection devices, facilitates the operation of electrical installations, including generators of power plants, and also reduces the cost of distribution networks equipment. It is indicated that the smallest power loss in a three-phase distributed power transmission system using high-temperature superconducting cables can be achieved with a symmetrical load operation mode. The results of technical analysis can be used to develop recommendations for improving the characteristics of cable power lines.

Feasibility study of high temperature superconducting cables for distribution power grids in metropolises

High temperature superconducting (HTS) cables have numerous advantages compared with conventional power cables, such as high power density and low power losses, therefore they have great potential to enhance the transmission capacity and improve the quality of power grids. In this work, we studied various cases to evaluate the feasibility of replacing conventional cables with HTS cables in metropolitan distribution networks. These cases represent three principal strategies. The first, HTS cables are applied at the same or lower voltage levels with the same transmission capacity, named ‘equal capacity replacement’. The second, considering increasing power demands we demonstrate how HTS cables can benefit power grids by providing expanded capacity (expanded capacity replacement). For the third, we consider the case of unequal routes from the perspective of saving land resources (unequal routing replacement). In this paper, we introduce the methods and results of this study and give some preliminary conclusive remarks.

Transmission Investment and Expansion Planning for Systems With High-Temperature Superconducting Cables

Growing electric power demand in densely populated metropolitan areas presents problems due to the lack of availability of space to build transmission lines and due to short-circuit current limits. One of the solutions to meet the increasing demand is high-temperature superconducting (HTS) cables, which have a sufficiently high capacity and can be installed in the limited space of existing ducts. However, since the characteristics of low-impedance HTS cables result in higher system short-circuit levels, fault current limiter (FCL) HTS cables have been developed to solve the fault current problem without an upgrade of the rating of the existing circuit breakers, which is typically necessary when new power facilities in the power system are installed. This paper investigates the impacts of the installation of HTS cables on optimal transmission expansion planning (TEP). A three-stage TEP framework (identification, system analysis, and optimization) is proposed to select between plain HTS or FCL-HTS cables, and to determine the locations of new transmission expansion lines. The TEP optimization problem is formulated using mixed integer linear programming with the big-M method. The simulation results showed that the benefits of installing the FCL-HTS cable can justify their high installation costs.

Influence of flow rate and heat flux on the temperature distribution in long length counter flow cooled cold dielectric HTS cables

The technical advantages of using High Temperature Superconducting (HTS) cables have drawn the attention of most of the researchers around the world. However, the cooling design of these cables nevertheless remains a challenge for the researchers and manufacturers. Therefore, in the present work, an attempt has been made to ease the challenge of cooling of long length High Temperature Superconducting (HTS) cables. Counter flow cooling arrangements of liquid nitrogen (LN2) have been proposed and analysed the longitudinal temperature distribution along the superconducting cable using heat balance equations. Also, in the present work the solution for the temperature distribution profiles of LN2 in counter cooled HTS cable are also obtained assuming one dimensional (1-D) model. In particular, nonlinear axial temperature profiles of LN2 in the counter cooled HTS cable are found. The single phase cold dielectric HTS cable with stainless steel corrugated pipes as flow paths are used for the analysis. Liquid nitrogen with varying volumetric flow rates of 20–35 L/min and total heat loss (A.C. loss and exterior heat load) of 2.3–2.6 W/m reveals interesting facts about cooling of cables with longer lengths. The defined cable length range at constant diameter (inner and annulus pipe) for the analysis was considered as 1.5–3 km. As a result, the maximum possible HTS cable length of 2.5 km can be achieved at the flow rate of 30 L/min and heat fluxes of 2.3–2.6 W/m within the defined operating range.

A Smart Overvoltage Monitoring and Hierarchical Pattern Recognizing System for Power Grid with HTS Cables

As one part of the power system, high-temperature superconducting (HTS) cables may be subject to various system faults, such as overvoltage. When overvoltage occurs, HTS cables may quench and the resistance of HTS tapes will increase rapidly, which will result in reduction of transmission capacity, increase of power loss and even electrical insulation breakdown. To protect the operation safety of power system, the level of overvoltage should be investigated in the system. This paper proposes a non-contact variable frequency sampling and hierarchical pattern recognizing system for overvoltage. Lightning and internal overvoltage signals are captured by specially designed non-contact voltage sensors. The sensors are installed at the grounding tap of transformer bushings and the cross arm of transmission towers. A variable sampling technique is employed to solve the conflict between sampling speed and storage capacity. A hierarchical pattern recognizing system is proposed to subdivide each overvoltage into specific types. Seven common overvoltages are discussed and analyzed. Wavelet theory and S-transform singular value decomposition (SVD) theory are adopted to extract the feature parameters of different overvoltages. Particle swarm optimization is employed to maintain a high classification rate and improve the initial set of the support vector machine (SVM) used as recognition algorithm. Field-acquired overvoltage data from an 110 kV substation validate the effectiveness of the proposed recognition system.

Entropy Generation Minimization (EGM) in High Temperature Superconducting (HTS) cables for optimization of thermohydraulic performance

High Temperature Superconducting (HTS) cables have potential merits of large current carrying capacity and compactness with reduced transmission losses and Right-of-Way (RoW) compared to conventional transmission power cables. However, internal forced convective cooling is necessary to cool HTS cables using cryogenic coolant such as liquid nitrogen (LN2) to retain the superconductivity for efficient power transmission. Due to forced convective cooling, inevitable pressure drop occurs in these cables and result in development of temperature and velocity gradients. Further, the accounted temperature and velocity gradients in HTS cables lead to volumetric entropy generation which causes reduction in thermohydraulic performance.The present work focuses at investigating the volumetric entropy generation rate in HTS cable. Further, Entropy Generation Minimization (EGM) technique is used as an optimization tool to estimate the minimum volumetric entropy generation rate to optimize thermohydraulic performance in HTS cables. Furthermore, pumping power and cooling capacity at minimum entropy generation rate are calculated. Computational Fluid Dynamics (CFD) is used to analyze the pressure drop and heat transfer rate for different flow rates to estimate the friction factor, pumping power and cooling capacity with flow of LN2 in corrugated former in HTS cable. A 3D computational geometry is developed using commercial software ANSYS®. Relevant boundary conditions are imposed on the computational geometry to reflect the practical operating conditions of HTS cable. Finite Volume Method (FVM) of discretization is used to solve the governing equations in order to obtain pressure drop and heat transfer rate in HTS cables. The simulated results are validated with the results available in literature. From the analysis, it is identified that at a heat load of 2.1 W/m and at an inlet temperature of 77 K, optimum cooling capacity and pumping power with minimum entropy generation rate are possible at a flow rate of 14 L/min.

Time–Frequency-Based Condition Monitoring of 22.9-kV HTS Cable Systems: Cooling Process and Current Imbalance

In this paper, new time–frequency-based anomaly detection methodology is proposed for the condition monitoring of high-temperature superconducting (HTS) cable systems. The time–frequency-based anomaly detection methodology includes two indices, which are obtained via cross Wigner–Ville distribution and scattering parameter. For the validation of the proposed methodology, the methodology is applied to an ac 22.9-kV/50-MVA HTS cable system connected to the real power grid network. Furthermore, the changes in dielectric properties of the HTS cable system during the cooling process and the current imbalance failure are monitored. The proposed anomaly detection indices are shown to be able to detect the heat and the current imbalance caused by the malfunction of the joint box. For the application of the two validated indices, new anomaly detection procedure for HTS cable systems is also presented.

Influence of corrugation topology on thermohydraulic performance of cold dielectric counter cooled high temperature superconducting cable

Fluid flow, pressure drop and heat transfer across the long length cold dielectric counter cooled High Temperature Superconducting (HTS) cables are significantly influenced by the different corrugation (rectangular, circular and triangular) topologies. Thus, in this present work, thermal and hydraulic characteristics of turbulent LN2 flow in counter cooled HTS cable with various corrugation topologies are computationally investigated. The 2-D axisymmetric model of HTS cable with counter flow cooling system is considered by changing the corrugation shapes for Reynolds number ranging from 3.0 × 104 to 6.0 × 104. Heat flux from ambient temperature on outer corrugated pipe and heat generation from A.C. losses in the HTS tapes are also considered in the present simulations. In addition, distribution of the velocity, temperature and turbulent kinetic energy (TKE) of liquid nitrogen (LN2) in the HTS cable with various corrugations are estimated using computational fluid dynamics (CFD) technique. Finite volume method is adapted to solve the governing equations (continuity, momentum and energy) using Semi-Implicit Pressure Linked Equations (SIMPLE) scheme with k−ε turbulence model and enhanced wall treatment. The results reveal that the corrugation topologies (rectangular, circular and triangular) have significant effect on heat transfer and pressure drop. The corrugated pipes with different topologies exhibit different friction factors due to the variations in the contact of wall surfaces with the LN2. Moreover, the calculated friction factors for all the three corrugation topologies are compared with the experimental results available in the literature. Further, the results of temperature difference between outlet and inlet temperatures of LN2 are validated with the available experimental measurements. Finally, it was concluded that the effect of heat flux and AC Losses on cooling capacity and heat transfer is found to be significant as compared that on friction factor and pumping power.

An effective design for induced current reducing of a single-phase multi-layer HTS coaxial cable with former

High temperature superconducting (HTS) cables require a former layer to bypass fault currents and support superconducting tape. The former layer of the HTS cable does not conduct current in steady-state operation due to the resistance difference with the conducting layer. However, in practice, an induced current flows through the former layer due to the mutual interaction with the conducting layer. Therefore, the current distribution in the cable should be uniform and the induced current in the former layer must be minimized. This paper deals with an effective design of a single-phase multi-layer HTS coaxial (SMHTSC) cable with former layer. The optimal combination of the pitch length and the winding direction in the conducting layer and the shield layer was selected for uniform current distribution of the SMHTSC cable and minimization of induced current in the former layer. The current distribution of the SMHTSC cable was analyzed based on the numerical calculation results obtained using the impedance matching method. The results and discussions of the current distribution on the SMHTSC cable with and without former layer were compared and presented.

A Feasibility Study of Smart High-Temperature Superconducting Cable to Improve Stability of KEPCO System

The Korean power system is a very tightly coupled island system. The installed capacity is about 100 GW and the load demand is gradually increasing. Especially in metropolitan areas where the load is concentrated, the system fault current often exceeds the breaker capacity due to the strong connection. The system operator limits the fault current by bus split operations considering the breaker capacity but this reduces system stability. Therefore, various efforts have been made using a fault current limiter to overcome these problems. A smart superconducting (SC) cable is a type of SC power transmission cable. It has not only standard structure of the existing SC power cable but also a fault current limiter. The cable has a SC characteristic in a normal state, while when a fault occurs, it can limit a fault current through generating impedance that adjusts electrical and thermal properties of SC cable and material and cross-sectional area of SC cable. In this paper, a technique is proposed to reduce system fault current while improving the system stability using a smart high-temperature SC cable. In addition, the appropriate cable capacity and locations are selected to improve the reliability of the Korean power systems using the smart SC cables. The proposed locations and capacities will be applied to the smart SC cable development project that started in May last year

Numerical study on critical current and AC loss for different structured stack slotted-core HTS cables

AC losses occur when high temperature superconducting (HTS) cables are connected by alternating current placed in alternating background magnetic field. The generation of AC loss will increase the load of cooling system, and deteriorate the overall performance of cables. Therefore, AC loss of high temperature superconducting cable is an important design parameter of large-scale power application. Up to now, AC loss characteristics of various HTS cables such as conductor on round core (CORC) cable, twisted stacked tape cable (TSTC), Roebel cable, quasi-isotropic strand and soldered-stacked-square-twisted (3S-T) wire have been extensively studied. AC loss characteristics of twisted-stack slotted-core cable, however, have not been studied. In this work, the self-field and in-field AC losses and critical currents of different structured stack slotted-core cables are studied numerically in two-dimensional. The critical current calculation using self-consistent model was based on the A-formulation and the H-formulations to assessment the AC losses. The numerical results are useful for the application of HTS cables.

Characterization of High-Temperature Superconducting Tapes

This paper presents an experimental method for investigating the dependence of critical current on the applied magnetic-field intensity and the angular orientation in high-temperature superconductor (HTS) tapes and cables. Comparisons between critical-current measured and simulated data are presented as a function of field angular orientation. The obtained relation can be used as input data for numerical calculations or simulations for designing application devices that utilize HTS tapes and cables.

Design and Experimental Research on Self-Shielding DC HTS Cable Model With Large Current Capacity

DC high-temperature superconducting (HTS) cable has advantages over the ac HTS cable in the power transmission due to its zero Joule loss, higher current capacity, and controllability. To minimize the magnetic field influence and critical current degradation in dc HTS cable, we have ever proposed a new structure of dc HTS cable that is, self-shielding dc HTS cable which has interleaved winding configuration. In this paper, in order to solve the difficulty of current lead connection with HTS layer in the cable terminal with multilayers, we put forward a new kind of terminal configuration which can make the current in each layer being controlled individually and avoid soldering in terminal as well as be convenient for installing and disassembly. With this kind of terminal connection method, a dc HTS model cable with eight layers and 1900 mm in length is fabricated and tested in liquid nitrogen temperature. Uniform current distribution among layers is realized by adjustable resistance connecting with each layer. The experimental results show that the critical current degradation of self-shielding dc HTS cable is only 7% compared with the critical current in self-field while the traditional structure of dc HTS cable is about 20%, which indicates that the self-shielding cable can promote the current capacity effectively with lower critical current degradation and save more HTS tapes in the application of power transmission. So, this kind of cable with a thinner insulation layer is suitable for mid- and low-voltage situations, especially for industrial and ship situations where large current and low voltage are required.

Recent Progress and Design of Three-Phase Coaxial HTS Power Cable in Korea

High-temperature superconducting (HTS) power cables were developed recently and have several advantages over conventional cables. For high current capacity, two or more layers are required in one phase of the HTS cable. Differences in the radii between each phase and layer cause inherent imbalance and non-uniform current distribution of three-phase currents. These outcomes must be minimized by properly designing the pitches of multi-layer three-phase coaxial HTS cables. In this paper, the authors design the conduction layers of a multi-layer three-phase coaxial HTS cable and analyze the characteristics of the designed cable based on the proposed PSCAD/EMTDC component and simulation method. A 23 kV/60 MVA multi-layer three-phase coaxial HTS power cable is considered. The conceptual design of a multi-layer three-phase coaxial HTS cable includes the radii of each layer, the number of layers in each phase, and the pitch design of each layer of the cable. Using an impedance matching program, current imbalance can be minimized and current distribution can be made uniform in all layers of the phase by adjusting the pitch length and winding direction. The characteristics of HTS cables using the proposed PSCAD/EMTDC component are analyzed. In this component, the dynamic resistance of current- and temperature-dependent HTS cables is added to the HTS model. AC losses are calculated using the some equation. Induced current loss is calculated based on the material properties of the shield layer. A transient simulation is performed for a three-phase fault of the three-phase coaxial HTS cable using a PSCAD/EMTDC-based simulation method.

Insulation Characteristics of PPLP in GHe and Design of 10 kV Bipolar Coaxial HTS DC Cable

Electrical insulation is an essential component of high temperature superconducting (HTS) dc cable systems and polypropylene laminated paper (PPLP) and has been widely used as insulation material for cold dielectric (CD) HTS cables due to its excellent dielectric mechanical properties. In this paper, mini-model cables were fabricated to simulate CD-type HTS cables and the insulation tests were carried out. DC and the lightning impulse breakdown strength of the 1% Weibull distribution of PPLP at 0.3 MPa helium gas (GHe) were investigated. Based on these results, the insulation design of a 10-kV bipolar coaxial HTS dc cable was performed. Furthermore, a model cable was manufactured according to the insulation design and tested for dc and impulse withstand voltage, which verified that the insulation design was qualified.

Mechanical Utility Structure for Testing High Field Superconducting Dipole Magnets

The U.S. Magnet Development Program (MDP) collaboration is designing a utility mechanical structure for testing various high-field superconducting dipole coils. The design uses a shell-based structure concept, which allows applying preload in two steps: during a room temperature assembly and during a cool down to a cryogenic temperature. The structure is designed to accommodate various coil designs-including Nb3Sn Cosine Theta (CT) and Canted CT magnets as well as hybrid magnets with high temperature superconductor cables. Superconducting coils, enclosed by bolted pads to form an octagonal coil pack, will be inserted into a reusable yoke-shell subassembly and precisely preloaded during the assembly using a bladder-and-key technology. Due to a differential thermal contraction between an external aluminum shell and the magnet core, the coil preload increases during the cool down up to level required for 17-T excitation. Such a reusable structure will serve as a testing fixture supporting goals of the MDP program, decreasing cost and simplifying coil performance testing at different preload levels. We present a finite-element analysis of the structure preloading various coil designs and examine the predicted coil stress at each step of the magnet assembly and excitation.

Failure Analysis of YBCO Tapes Considering the Amplitude and Duration of Sinusoidal Overcurrent

The ultimate current-carrying capacity of high-temperature superconducting (HTS) tapes is extremely important for the design of superconducting devices, especially for superconducting fault current limiter and HTS cables which may be subject to short-circuit overcurrent. In this paper, an HTS tape life characteristics test platform was built, and experiments were carried out on the YBCO tape to study its ultimate current-carrying characteristic under 50 Hz ac current. AC overcurrent amplitude and duration are used as experimental variables. According to the single variable method, the current and voltage of the YBCO tapes under different types of overcurrent were measured. After analyzing and generalizing the test results, the thresholds of its bearable current and corresponding duration are discussed. This paper provides data support and reference for the reliable design of these HTS power devices.

Numerical Model of HTS Cable and Its Electric-Thermal Properties

High-temperature superconducting (HTS) cables have significant advantages in large-capacity and long-distance transmission. In order to analyze the operation characteristics of HTS cables in ac power system, this paper develops a numerical model to research its electric and thermal properties in transient process. Different from the model built by finite-element method in COMSOL, this model is built in MATLAB/SIMULINK for faster calculation and simpler modeling process. Besides, it is compatible with the power system simulation. Based on the structure of HTS cables, the model is built by an equivalent circuit and an electrical-analog method. The author tested the model by comparing it with a model built in COMSOL, to verify the effectiveness and advantages. The simulation result illustrates that the proposed model helps analyze the electric and thermal property of cables during transient process in power system quickly and efficiently.

Impact of Smart HTS Transmission Cable to Protection Systems of the Power Grid in South Korea

In South Korea, Korea Electrotechnology Research Institute (KERI) has developed a 154 kV smart High Temperature Superconducting (HTS) cable system with fault current limiting function since May 2017. This project is funded by the Ministry of Trade, Industry, and Energy of Republic of Korea. It is very important to design the protective relay system for a successful application of the smart HTS cable system to a practical power grid. In general, the smart HTS cable can have a negative impact on the protective coordination in power transmission system because of the variable impedance of the cable. This paper reviews some protection problems which can be caused by the application of the 154 kV smart HTS cable to power transmission systems in Korea and proposes a protection scheme for a test power system. And then we conduct a basic study to find solutions for the problems using an electromagnetic transient program, PSCAD/EMTDC.