There are high expectations for coated conductors in electric power applications such as SMES, power cables and transformers owing to their ability to contribute to stabilizing and increasing the capacity of the electric power supply grid, as well as reduce CO2 emissions based on their high critical-current characteristics. R&D has been performed on wires and power devices as part of many national projects all over the world. The Materials & Power Applications of Coated Conductors (M-PACC) project is a national project in Japan supported by the Ministry of Economy, Trade and Indstry (METI) and the New Energy and Industrial Technology Development Organization (NEDO) to develop both coated conductors that meet the market requirements and fundamental technologies for power applications using coated conductors. Three years have passed since this five-year national project started in fiscal 2008. In this article, R&D results are reviewed and compared with the interim/final targets of the project, and the future prospects are discussed.
A new Japanese national project has started in 2008 to develop high temperature superconducting electric power devices. In this project, we have developed a superconducting magnetic energy storage (SMES) system, which are highly expected as a stable power supply. Main issues are a large current capacity conductor made of YBCO-coated tapes and a compact coil wound the conductors. Aiming at the manufacturing of compact coil with higher energy density through the creation of higher magnetic field, we produced YBCO coil, and by carrying out hoop stress tests. Also, aiming at the development of 20 MJ class SMES component coils necessary for picturing the technological outlook of 2 GJ class SMES coil for power system control, we manufactured component coils (outer diameter 650 mm), adopting the bundled conductor that would enable the realization of high strength and low loss, proving that its current capacity was large enough to exceed 2.6 kA, through basic verification test for energization. In addition, we have challenged the development of high efficiency coil conduction cooling technology, stable manufacturing technology of coated conductors for SMES and the highly reliable/highly durable SMES coil component technology.
There are expectations for high-temperature superconducting (HTS) power cables as a compact cable with large capacity and low-loss power transmission. Recently, the stable manufacture of many long REBCO (RE = rare-earth element) tapes has been achieved. REBCO tapes have a high critical-current density, and the AC loss resulting from the parallel magnetic field is extremely small because of the thin-film structure of the superconducting layer. The basis of the M-PACC (Materials & Power Applications of Coated Conductors) project is to develop a process technology for fabricating REBCO tapes and promote development aiming toward the commercialization of superconducting cables using REBCO tapes. Two types of HTS cables are being developing as part of this project. These cables have superior transmission efficiency, lower loss and larger capacity than existing power cables. One is a 66 kV/5 kA three-core large-current cable and the other is a 275 kV/3 kA single-core high-voltage cable. There are several development targets. We examined factors such as AC loss, thermal characteristics of the cables under over-current and the optimum cable design. This paper provides an overview of the project and describes its progress.
REBCO superconducting power transformers, which are incombustible, lightweight and compact, are expected to have practical applications in equipment for substations and office buildings in urban areas. In recent years, there have been remarkable improvements in the performance of REBCO tape wires, which have the characteristic of a large critical current in highly magnetic fields. Their use is expected to reduce AC loss through the application of slit processing on the tape wire. Based on these advantages, the authors have developed element and system technologies of REBCO power transformers. Wire-scribing technology, coil-winding technology (for example, short-circuit characteristics), cryogenic technology, fault current-limiting (FCL) technology and a design study of a 66 kV/6 kV, 20 MVA transformer are examined.
This is a review of the current status of R&D for coated conductors in the Materials & Power Applications of Coated Conductors (M-PACC) project. In the previous project, the production of tapes with high Ic×L in excess of 250 kAm was achieved, leading to the development of electric power applications being started. However, future application requirements are much higher than those at present. In this project, coated conductors for future applications have been developed to realize the specific performance requirements for each application according to five different sub-themes; degradation, higher in-field Ic, lower AC losses, higher mechanical strength, and higher Je and lower cost. During the three-year development, the interim targets were almost satisfied and the activities performed were at the top technical level in the world. We are now in the final stages of development, aiming to achieve the final targets, which are based on the specifications for marketing the cables, transformers and SMES.