Tri-axial High Temperature Superconducting Power Cable Research Articles

Thermo-Hydraulic Analysis of a Tri-Axial High-Temperature Superconducting Power Cable with Respect to Installation Site Geography

Various high-temperature superconducting (HTS) power cables are being developed or are ready for commercial operation to help energy suppliers meet the growing power demand in urban areas. Recently, triaxial HTS power cables have been developed by Korea Electric Power Corporation (KEPCO) and LS Cable & System. Further, KEPCO has been planning to install a 2 km long 23 kV/60 MVA triaxial HTS power cable to connect the Munsan and Seonyu substations and increase the stability of the power grid. The HTS power cables should be cooled down to a cryogenic temperature near 77 K. A thermo-hydraulic analysis of the cooling system considering the geographical characteristics of the installation site is essential for long-distance sections. This paper describes the thermo-hydraulic analysis of the triaxial HTS power cable to determine the proper mass flow rates of subcooled liquid nitrogen that meet the operating temperature and pressure of the cable for four configurations of cooling systems: (1) a single cooling system with an external return path, (2) a dual cooling system with an external return path, (3) a single cooling system with an internal return path, and (4) a dual cooling system with internal return path. Since the flow characteristics in a corrugated cable cryostat differ significantly from those in a typical annular tube, a computational fluid dynamics (CFD) analysis was conducted to estimate the pressure drop along the cable cryostat. With the CFD analysis and given heat loads in the cable, the temperature and the pressure variations along the cable were calculated and their pros and cons were compared for each configuration of the cooling system. This thermo-hydraulic analysis will be referenced in the actual installation of the HTS power cable between the Munsan and Seonyu substations.

Feasibility Assessment of the New Configuration of an Electric Power Grid with 23 kV Tri-axial HTS Power Cables for an Urban Power Supply

The advantage of high temperature superconducting (HTS) power cables is that they can transmit large amounts of power at relatively low voltages, which can be used to reduce the number of lines in transmission cables or to configure a power grid at lower voltages. Because the commercial operation of 23 kV HTS power cables has begun, the optimal configuration between the 154 kV transformer substations and the 23 kV switching stations connected by the 23 kV HTS cables must be reviewed. In this paper, the new power supply model using 23 kV tri-axial HTS cables is presented for an urban power supply, and the economic feasibility is reviewed to present the appropriate cable capacity selection that matches the 23 kV switching stations.

Performance Analysis of Real-Scale 23 kV/60 MVA Class Tri-Axial HTS Power Cable for Real-Grid Application in Korea

Currently, various types of superconducting power cables are being developed worldwide, and research and development of a tri-axial high-temperature superconducting (HTS) power cable are underway. The tri-axial HTS power cable reduces the amount of HTS wire due to its multilayer structure, has high current characteristics, and has less loss than other superconducting cables. However, since the radii of each phase are different, magnetic coupling makes it difficult to measure power loss and analyze performance. This paper presents the results of the design and performance analysis of a tri-axial HTS power cable. A prototype tri-axial HTS power cable was designed with a rated power of 60 MVA, a rated voltage of 23 kV and a length of 6 m, and was tested by cooling to 77 K with liquid nitrogen. We analyzed the performance of the tri-axial HTS power cable in normal conditions through a finite element method (FEM) simulation and experiment. The alternating current (AC) loss of the tri-axial HTS power cable was calculated using a FEM program based on the Maxwell equation, and the result was used to confirm the AC loss of the tri-axial HTS power cable prototype measured by the electrical measurement method. In conclusion, in the current test of a tri-axial HTS cable designed as 23 kV/60 MVA, the DC critical current was over 6000 A, the AC loss was approximately 0.24 W/m, and the simulation and analysis design values were satisfied. The results of this study will be effectively applied to commercial tri-axial HTS power cable development to be installed in a real power system. This means that the actual tri-axial HTS cable has sufficient capacity for rated current operation in the system where it will be applied, and the actual measurement of the cable loss can be applied as an important factor in the design of the cooling capacity of the entire superconducting cable, which consists of several kilometers.

Economic Evaluation of 23 kV Tri-Axial HTS Cable Application to Power System

Research on the development of a superconducting power cable for commercialization is currently underway across the world. Many demonstrations of superconducting power cables connected to real power grids have already been conducted with various designs depending on the voltage levels of the distribution and transmission lines. In Korea, the first commercial project for high temperature superconducting (HTS) power cables, “Shingal Project” which is fully funded by Korea Electric Power Corporation (KEPCO), is underway to connect two substations with a 23 kV HTS cable with a distance of 1 km. In addition, the KEPCO Research Center (KEPRI) initiated the project in 2017 to develop the 23-kV tri-axial HTS power cables, including a cooling system, for a distance of 3 km. In this paper, the recent progress and research activities related to the two 23-kV superconducting power cables projects are discussed. An economic evaluation of the HTS power cables for commercialization in consideration of their construction environments and social issues is also presented.

RTDS-based Model Component Development of a Tri-axial HTS Power Cable and Transient Characteristic Analysis

The transient characteristics of the tri-axial High Temperature Superconducting (HTS) power cable are different from those of a conventional power cable depending on whether the cable is under a steady or transient state due to the quench. Verification using simulation tools is required to confirm both the characteristics of the cable and the effect of the cable when it is applied to a real utility. However, a component for the cable has not been provided in simulation tools; thus the RTDSbased model component of the tri-axial HTS power cable was developed, and a simulation was performed under the transient state. The considered properties of model component include resistance, reactance and temperature. Simulation results indicate the variation of HTS power cable condition. The results are used for the transient characteristic analysis and stability verification of the tri-axial HTS power cable. In the future, the RTDS-based model component of the cable will be used to implement the hardware-in-the-loop simulation with a protection device.

Transposition-Based Connection Scheme and Joint Box Concept for a Tri-Axial HTS Power Cable

Tri-axial high temperature superconducting (HTS) power cables are being developed to maximize their advantages, which include reducing amount of HTS wires, having a low-leakage magnetic field, and being compact compared to different types of HTS power cables. However, a drawback of HTS power cables is their inherent imbalance impedance, which is due to an asymmetrical structure on each phase. To solve this problem, the phases must be transposed. The authors designed a distribution class tri-axial HTS power cable, as well as a transposition-based connection scheme for the cable. The phases of the cable were connected to each other via transposition through their cross-connections. This was achieved with an insulated support structure with three walled-off areas for insulation between three the phases, as well as transposition conductors, including copper base and HTS wires. In this paper, a distribution class tri-axial HTS power cable and a connection scheme for it are designed. The results, including the transposition-based joint box design, are described in detail. The connection scheme will be applied to the joint box of the cable for high-capacity and long-distance transmission.

Design and PHILS-based Transient Analysis of a Tri-axial HTS Power Cable

Tri-axial high-temperature superconducting (HTS) power cables are very efficient compared with other HTS power cables due to their reduced use of HTS wires and cryogenic surface area, resulting from the mutually layered structure of the three phases. However, the operating characteristics of tri-axial HTS power cables differ from other cables in a transient-state condition. In order to install HTS power cables in a real grid, feasibility verification through simulation or experimentation is required in advance. Thus, the authors design a tri-axial HTS power cable and implement a power hardware-in-the-loop simulation that consists of a real time digital simulator-based simulation model and hardware devices including a power supply and a 1 m-long tri-axial HTS model cable. Simulation results show the stability verification under steady-state and transient-state conditions.

Transient Characteristic Analysis of a Tri-Axial HTS Power Cable Using PSCAD/EMTDC

The characteristics of the tri-axial high temperature superconducting (HTS) power cable are different from a general copper cable, depending on whether the cable is under steady state or transient state, which is caused by quench. Before applying the tri-axial HTS power cable to a real utility, the system should be analyzed using certain simulation tools in order to confirm the effects of the cable on the real utility. However, a component that has the same impedance characteristics as the real tri-axial HTS power cable is not provided in simulation tools. In this paper, a model component for the tri-axial HTS power cable was developed in PSCAD/EMTDC. The developed model component included characteristics of the HTS cable, such as resistance, reactance, and temperature variation. The model component for the tri-axial HTS power cable was applied to a model power system and a simulation was performed under transient state. The simulation results show the effect of the tri-axial HTS power cable on the power system, the variation of quench resistance, and the temperature of the cable under fault conditions according to superconducting characteristics. The results of this work will be used to analyze the transient characteristics of other types of HTS power cables.

Development and Performance Analysis of a 22.9 kV/50 MVA Tri-axial HTS Power Cable Core

Tri-axial high-temperature superconducting (HTS) power cables are being developed to maximize their advantages such as reduced amount of HTS wires, a low-leakage magnetic field, and compactness compared with the different types of HTS power cables. The authors designed a 22.9 kV/50 MVA-class tri-axial HTS power cable core to apply to the distribution system in Korea. The inherent imbalance in the three-phase currents of the tri-axial HTS power cable core was calculated using the impedance matching program. A tri-axial HTS power cable core was fabricated using second-generation YBCO wires and the cable core was tested under 77 K liquid nitrogen to verify the performance of the cable core through obtaining its electrical characteristics data. This paper describes the results of the design, fabrication, and evaluation of the 22.9 kV/50 MVA-class tri-axial HTS power cable core. They will be used to develop a tri-axial HTS power cable for the distribution system.

Development of an Impedance Matching Program for Balancing the Current Distribution in a Tri-axial HTS Power Cable

The tri-axial high temperature superconducting (HTS) power cable design has several advantages when compared with other HTS power cables. However, this design has an imbalance in the three phase currents, as the phase conductors of the tri-axial HTS power cable have different radii. The radii of the phase conductors impact the value of inductance and capacitance for the cable, and the values are determined by the winding pitch length and the winding direction. Thus, the current imbalance can be minimized through the adjustment of the winding pitch length, the radius of each layer, and the winding direction. It takes a lot of time to manually calculate an impedance and to find a matched impedance. So the impedance of the tri-axial HTS power cable, according to its shape, was analyzed and the impedance matching program (IMP) was developed using LabVIEW (Laboratory Virtual Instrument Engineering Workbench) to solve this problem. IMP finds the matching impedance automatically by calculating the impedance according to the tri-axial HTS cable dimension. Consequently, this could save a lot of time, and so this program will be applied to the design of the tri-axial HTS power cable effectively.

Design and AC Loss Analysis of a 22.9 kV/50 MVA Class Triaxial HTS Power Cable

Recently, triaxial high temperature superconducting (HTS) power cables have become a mainstream design in the development of HTS cables because of several advantages, such as the reduced amount of HTS wire, low leakage fields, and compactness, when compared with other types of HTS cable. Unlike the AC loss from other types of HTS cable, the AC loss from the triaxial HTS cable is influenced by the magnetic fields of other phases, as the triaxial HTS cable does not have a shield layer between the phase conductors. The authors have designed a 22.9 kV/50 MVA class triaxial HTS power cable. The AC loss and the magnetic characteristics of the triaxial HTS power cable are analyzed using the Comsol program, a commercial finite element method. To confirm the characteristics of the triaxial HTS power cable by wire type, the characteristics of two wire types were applied to the FEM model.

Electrical Model of Balanced AC HTS Power Cable

The future electricity grid will be more sustainable and it will have more power transmission and distribution capability with more electrical power added from decentralized sources on distribution level and from wind parks and other large sources on transmission level. More interconnections and more underground transmission and distribution will be put up. Use of high temperature superconducting (HTS) power cables provides solutions to many of the future grid problems caused by these trends. In this paper we present an electrical model of a balanced 6 km-long three phase triaxial HTS power cable for the Dutch project being developed by a consortium of Alliander, Ultera™ and TUD. The cable currents in all three phases are balanced by selecting proper twist pitches and insulation thickness. The paper focuses on determining inductances, capacitances and AC losses of the balanced cable. Using the developed model, we also determine the voltage drop as function of the cable length, the neutral current and the effect of the imbalanced capacitances on the current distribution of the Dutch distribution cable. The model is validated and it can be used for accurate simulation of the electrical behaviour of triaxial HTS cables in electrical grids.