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Sagamihara, Japan

Shibuya T.,NEC Corp | Nagase R.,Nippon Telegraph and Telephone | Takahashi T.,Showa Cable Systems Co. | Kubo D.,Seikoh Giken Co. | Matsuura H.,Furukawa Electric Group
Optics InfoBase Conference Papers | Year: 2010

High power damage threshold test and thermal simulation for plug-style optical attenuator were carried out. The degradation mode and its mechanism were clarified. The limit in high power level for assuring long-term reliability was confirmed. © 2010 Optical Society of America. Source


Li Y.,North China Electrical Power University | Wang Y.,CAS Institute of Electrical Engineering | Wang Y.,North China Electrical Power University | Miao J.,North China Electrical Power University | And 5 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2015

The high-temperature superconducting (HTS) strand, with high current capacity and a round or square cross section, is expected to have widely potential applications in current leads and superconducting power devices since it is easily insulated to avoid point charging. This paper describes a quasi-isotropic strand made from coated conductors. The magnetic field distribution and critical current characteristic of the strand in self-field are simulated by the finite-element method and tested in liquid nitrogen. The result indicates that this strand has high current-carrying capacity. The critical currents in different external magnetic fields and various orientations were measured. It is verified by the experiments that the strand has isotropic characteristics in low magnetic field and weak anisotropy in higher field. The potential of the strands with high engineering current density makes them also suitable for high-field magnets and high-voltage power applications, while maintaining flexibility. © 2002-2011 IEEE. Source


Kono H.,Waseda University | Wang X.,Waseda University | Ueda H.,Waseda University | Ishiyama A.,Waseda University | And 5 more authors.
Physica C: Superconductivity and its Applications | Year: 2010

In high temperature superconductor applications used in electric power devices, YBCO coated conductors may be subjected to short-circuit fault-currents that are 10-30 times the normal operating current. These over-currents cause heat generation, resulting in Ic degradation of the YBCO coated conductor. Therefore, it is necessary to fully investigate the degradation characteristics of YBCO coated conductors. We previously conducted preliminary experiments on the degradation of YBCO sample tapes resulting from the over-current pulse drive. In this study, we analyzed the waveform of fault-current that is supposed to flow into the YBCO coated conductor when a short-circuit fault occurs in a power cable application, by using a newly developed numerical simulation program. We also carried out experiments in which an over-current with the analyzed fault-current waveform was applied to two YBCO sample tapes. We then investigated the degradation characteristics, focusing on the amount of current permitted. Experimental results showed that both the sample tapes (initial Ic = 118.6 A and 123.2 A) were degraded by applying an over-current with a peak value of 320 A. © 2010 Published by Elsevier B.V. Source


Iwakuma M.,Kyushu University | Tomioka A.,Kyushu University | Otonari T.,Kyushu University | Ogata T.,Kyushu University | And 14 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

A single-phase 10 kVA transformer was designed and fabricated with RE 1Ba2Cu30O7-6 (REBCO, RE: Rare Earth) superconducting tapes to quantitatively investigate the transition phenomenon of REBCO superconducting tapes to normal state due to a fault excess current. The voltage ratio was 1:1 and the rated voltage was 393 V. It had four windings. The primary and secondary windings had auxiliary windings in addition to main ones respectively. The main and auxiliary windings were connected in parallel in the both sides. The addition of the auxiliary windings made it possible to observe the induced normal resistances in the respective main ones individually. First usual performance tests were carried out and a stable operation as designed was confirmed. In steady state almost all of the current flowed in the main windings due to the small leakage reactance between them. At a sudden short-circuit test, the main windings quenched due to excess current over the critical current and the current was reduced to one fortieth as compared with the case of no current limiting function. It was clarified the whole of the main windings did not shift to normal state though the current exceeded the critical current all over the length and the induced normal zone was almost proportional to the primary voltage. © 2010 IEEE. Source


Kabir M.,Akita University | Suzuki M.,Akita University | Yoshimura N.,Akita University | Shiozawa K.,Showa Cable Systems Co. | And 3 more authors.
IEEJ Transactions on Electrical and Electronic Engineering | Year: 2012

A measurement technique is developed to measure the characteristics of zinc oxide (ZnO) microvaristors directly. We used Cu wires, a micromanipulator, and an optical microscope to gain ohmic contact of the measurement apparatus with ZnO particles. With our system, the I-V characteristics and C-2-V characteristics were measured for 25 μm ZnO microvaristors. Our measurements show that these microparticles behave as varistors. Further measurement on the ZnO microvaristors and observation of their fine structure may help to understand the varistor behavior. It also can pave the way to the understanding of the electrical characteristics of grain boundaries as well as the double Schottky barrier formed at the grain boundaries. © 2011 Institute of Electrical Engineers of Japan. Source

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