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A test stand of a DC superconducting power transmission cable was finished to construct in October 2006 in Chubu University, Japan, and three cooling cycles were carried out to measure the properties of the cable. Critical current of HTS tapes in the cable was measured at every cooling cycle and shows the similar temperature dependence; conclusivel...
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Novel design options of HTS and LTS superconductor lines for fast-cycling accelerator magnets are presented. The cryogenic power losses in using these conductors in transmission line application to energize the accelerator magnet string are discussed. A test arrangement to measure power loss of the proposed superconductor lines operating up to 2 T/...
![Finite element model mesh for the original configuration [4]: 30 tapes...](publication/322764303/figure/fig3/AS:1086480009166863@1636048428514/Finite-element-model-mesh-for-the-original-configuration-4-30-tapes-distributed-in-5_Q320.jpg)
The ENEA superconductivity laboratory developed a novel design for Cable-in-Conduit Conductors (CICCs) comprised of stacks of 2nd-generation REBCO coated conductors. In its original version, the cable was made up of 150 HTS tapes distributed in five slots, twisted along an aluminum core. In this work, taking advantage of a 2D finite element model,...
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... So it is potential for future power transmission line such as power distribution line in large city, electrolysis, solar and wind electrical energy transmission with large current capacity and mid-or low voltage. There are several projects of DC HTS transmission systems carried out in the world [1]- [4]. Although the application of existing DC HTS cable [3] with high current capacity may lower the ultra-high voltage to some levels, there have been few DC HTS Power cable prototypes with current capacity larger than 10 kA [5]. ...
DC high-temperature superconducting (HTS) cables have advantages of high current capacity, low ac loss, and higher controllability compared with ac HTS cables. To minimize the magnetic field effect and the critical current degradation, a new configuration of dc HTS cables was ever put forward. This kind of cable has a self-shielding characteristic and a "sandwich" structure by interleaved winding. This paper presents a detailed magnetic field analysis of this structure such as the magnetic field in each layer. This magnetic field analysis confirms that this configuration can minimize the magnetic field in each layer and outer space, thus reducing the critical current degradation, and has self-shielding advantage. This structure is also compact and saves more material. Therefore, the cable is a potential HTS transmission line with large current capacity in the application of mid- and low-voltage dc power transmission.
... The modern level of development of power engineering and properties of HTS materials reached nowadays allow transmission of these power values at typical voltages (10-35 kV). Since there are a lot of obvious advantages of HTS DC cables, in many countries, e.g., in the USA, Korea, China, Japan etc. had begun works to construct these lines for various purposes [2][3][4][5][6]. ...
Previous research has shown that implementing high-temperature superconducting dc power cables in electrical grids of large metropolitan areas will have major positive impacts on power system operation and control. Current activities in Russia comprise developing a 2.5-km high-temperature superconducting dc cable and its installation in St. Petersburg electrical grid. This work includes five major parts: installation site selection, cable calculation, development and manufacturing, cryogenic equipment development, ac/dc converter development, and testing of all dc line elements. As of today, the list of subcontractors has been approved. The purpose of this report is to summarize current results and future work.
... Chubu University has already developed a 20-m class superconducting direct current (DC) superconducting transmission device (CASER-1) [4] and has proposed several technologies to improve system performance of superconducting applications. Discussions have been made concerning the current balance of superconducting tapes as stable transmission systems, low-heat leak systems using special cryogenic double pipes, etc. [5,6]. For actual applications, reducing heat leak to the low temperature part is the most important aspect of technology for high-performance superconducting applications. ...
Global energy problems should be solved quickly, and superconducting applications are highly demanded as energy saving technologies. Among them, long-distance superconducting transmission seems to be one of the most promising for energy saving by energy sharing. On the other hand, such large systems can be constructed from smaller network systems that can be enhanced by scaling up to the superconducting grid. Reducing heat leak to the low temperature end is the most important aspect of technology for practical superconducting applications, and heat leak reduction at the terminal is a key goal especially for small-length applications. At Chubu University, we have developed a 200 m-class superconducting direct current transmission and distribution system (CASER-2), in which we also used a Peltier current lead (PCL) as heat insulation at the terminal. PCL is composed of a thermoelectric material and a copper lead. In actual transmission and distribution applications, the cables are also cooled by the coolant. After the circulation, the coolant could also be used to cool the current lead. We will discuss the performance of such gas-cooled systems as the total performance of applied superconducting systems using the experimental parameters obtained in CASER-2.
... Laboratory demonstration of DC superconducting cable has been carried out at Chubu University in Japan. [19] A proposal for a DC superconducting electricity "pipeline" is shown in Figure 6. ...
The demand for carbon‐free electricity is driving a growing movement of adding renewable energy to the grid. Renewable Portfolio Standards mandated by states and under consideration by the federal government envision a penetration of 20‐30% renewable energy in the grid by 2020 or 2030. The renewable energy potential of wind and solar far exceeds these targets, suggesting that renewable energy ultimately could grow well beyond these initial goals.
The grid faces two new and fundamental technological challenges in accommodating renewables: location and variability. Renewable resources are concentrated at mid‐continent far from population centers, requiring additional long distance, high‐capacity transmission to match supply with demand. The variability of renewables due to the characteristics of weather is high, up to 70% for daytime solar due to passing clouds and 100% for wind on calm days, much larger than the relatively predictable uncertainty in load that the grid now accommodates by dispatching conventional resources in response to demand.
Solutions to the challenges of remote location and variability of generation are needed. The options for DC transmission lines, favored over AC lines for transmission of more than a few hundred miles, need to be examined. Conventional high voltage DC transmission lines are a mature technology that can solve regional transmission needs covering one‐ or two‐state areas. Conventional high voltage DC has drawbacks, however, of high loss, technically challenging and expensive conversion between AC and DC, and the requirement of a single point of origin and termination. Superconducting DC transmission lines lose little or no energy, produce no heat, and carry higher power density than conventional lines. They operate at moderate voltage, allowing many “on‐ramps” and “off‐ramps” in a single network and reduce the technical and cost challenges of AC to DC conversion. A network of superconducting DC cables overlaying the existing patchwork of conventional transmission lines would create an interstate highway system for electricity that moves large amounts of renewable electric power efficiently over long distances from source to load. Research and development is needed to identify the technical challenges associated with DC superconducting transmission and how it can be most effectively deployed.
The challenge of variability can be met (i) by switching conventional generation capacity in or out in response to sophisticated forecasts of weather and power generation, (ii) by large scale energy storage in heat, pumped hydroelectric, compressed air or stationary batteries designed for the grid, or (iii) by national balancing of regional generation deficits and excesses using long distance transmission. Each of these solutions to variability has merit and each requires significant research and development to understand its capacity, performance, cost and effectiveness. The challenge of variability is likely to be met by a combination of these three solutions; the interactions among them and the appropriate mix needs to be explored.
The long distances from renewable sources to demand centers span many of the grid's physical, ownership and regulatory boundaries. This introduces a new feature to grid structure and operation: national and regional coordination. The grid is historically a patchwork of local generation resources and load centers that has been built, operated and regulated to meet local needs. Although it is capable of sharing power across moderate distances, the arrangements for doing so are cumbersome and inefficient. The advent of renewable electricity with its enormous potential and inherent regional and national character presents an opportunity to examine the local structure of the grid and establish coordinating principles that will not only enable effective renewable integration but also simplify and codify the grid's increasingly regional and national character.
Compared with AC HTS cable, DC high-temperature superconducting (HTS) cable has prominent advantages of low transmission loss, large current capacity and high controllability. The current directions in adjacent layers of “sandwich” cable with self-shielding characteristic are opposite, which can greatly reduce the magnetic field influence and the critical current degradation. In order to homogenize the magnetic field distribution of the cable, an optimized self-shielding DC HTS cable is proposed. Compared with the previous structure, the optimized self-shielding DC HTS cable has a larger critical current and smaller ripple loss. In this paper, the magnetic field distribution and the ripple loss of three different DC HTS cables with ripple current are studied by a two-dimensional (2D) finite element method (FEM) based on T-A formulation. The 2D simulation model offers a valuable reference for the design and operation of DC HTS cable with low voltage and large current.
As is known, heat losses through current leads essentially determine the economic efficiency of the superconducting systems. Much attention is paid to the design of optimal current leads, but the Wiedemann-Franz law physically limits the benefits of the standard approach. An innovative way to further reduce heat inflow is to use current leads equipped with Peltier thermoelectric elements. These elements are installed in series in the power circuit. Therefore, when the transport current passes through the Peltier element, the thermoelectric effect counteracts the heat flow caused by the temperature gradient in the current lead. Another advantage of this design is that when the circuit is de-energized, the heat loss is reduced due to the low thermal conductivity of the Peltier element. In addition to the theoretical works devoted to the Peltier current leads (PCLs), many experiments confirmed a decrease in heat loss by about 30%. Moreover, PCLs were installed on 500- and 1000-meter HTS power transmission lines in Ishikari (Hokkaido, Japan). An advanced approach involves cooling the current-carrying parts with evaporating nitrogen, which should improve the performance of PCLs. In this work, an experiment on testing gas-cooled PCLs was carried out for the first time. A 30% additional reduction in heat inflow was achieved. At the same time, the dependence of the specific heat loss on the current became flatter, which means an expansion of the range of operating current. In the experiment, the vented gas passed through copper pipes used as conductors. In the future, to increase the efficiency of the gas-cooled PCLs, we plan to improve the heat transfer between the gas flow and the conductor using surface ribbing.
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 multi-layers, 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 8 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 percent comparing with the critical current in self-field while the traditional structure of DC HTS cable is about 20 percent, 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 thinner insulation layer is suitable for mid-and-low voltage situation, especially for industrial and ship situations where large current and low voltage are required.
Current lead, connecting dc superconducting device with power supply, is one of the major heat leakage sources. Reducing the heat leakage from the current lead to cryogenic system is very important in the operation of dc superconducting device. The Peltier current lead (PCL) is effective for reducing the heat-leakage. The PCL consisting of the conventional copper lead with a thermoelectric material Bi
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Te
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inserting into room-temperature end can be effective to reduce heat leakage due to its Peltier effect. For the sake of studying the higher current capacity of PCL, the 1-kA-class PCL was designed and fabricated in this paper. Dynamic stability experiment for the PCL was carried out such that its operating stability was confirmed. The temperature along the PCL was measured and the heat leakage per kA current
q
was also calculated. The experimental results showed that the PCL can be effective to reduce the heat leakage and has potential applications in the dc superconducting device.
Energy loss of HTS power transmission line is highly correlated to the properties of the vacuum thermal insulation. The distance between pumping stations is determined by pumping speed, conductance of the cryostat, and outgassing rate. In present report, the pumping of 1000 m long cryostat is considered on the example of Ishikari-2 project. Pumping of the cryogenic pipe is carried out through ports located at the pipe ends. 475 m long straight section No. 1 is equipped with heat radiation shield, whereas 137 m long U-bend section No. 2 and 379 m long straight section No. 3 are protected with conventional MLI. Experimental data allow us to estimate the lower limit of the pumping length. When using cryogenic pipe with heat radiation shield "as is", it is possible to provide the required level of vacuum for a length of 8 km in the nighttime and 5 km in the daytime, because outgassing rate correlates well with the temperature of outer pipe varied from 4 to 41 °C. If we will take measures against heating of the outer pipe and will redesign the radiation shield to improve conductance, the possibility to evacuate 10 km long cryostat by two vacuum pumps installed at the ends can be achieved. IEEE
