Observation of self-magnetic field relaxations in Bi2223 and Y123 HTS tapes after over-current pulse and DC current operation

• Published in: Cryogenics (Guildford) 2016-07, Vol.77, p.53-58
• Main Authors: Tallouli, M., Sun, J., Chikumoto, N., Otabe, E.S., Shyshkin, O., Charfi-Kaddour, S., Yamaguchi, S.
• Format: Article
• Language: English
• Subjects: BSCCO tape; COMPUTER SIMULATION; COPPER OXIDE; Current density; Current density profile; DENSITY; Direct current; Hall probe measurement; Hall probes; Inverse problems; MAGNETIC FIELD; Magnetic relaxation; Over-current pulse; Power lines; Simulation; SUPERCONDUCTORS; TAPE; Transport; YBCO superconductors; YBCO tape; YTTRIUM OXIDE
• ISSN: 0011-2275; 1879-2235
• DOI: 10.1016/j.cryogenics.2016.04.010

•An over current pulse for some milliseconds and DC current is applied to BSCCO and YBCO tapes.•Hall probe measures self-magnetic field near the tapes’ edge and scans the self-magnetic profiles.•Linear equations of the inverse problem are calculated and current density profiles are shown.•Over-current pulse and normal operations are compared.•Change of the self-magnetic fields and current loop in HTS tapes are observed. The development of power transmission lines based on long-length HTS tapes requires the production of high quality tapes. Due to fault conditions, technical mistakes and human errors during the operation of a DC power transmission line, an over-current pulse, several times larger than the rated current, could occur. To study the effect of such over-current pulses on the transport current density distribution in the HTS tapes, we simulated two start-up scenarios for one BSCCO and two YBCO tapes. The first start-up scenario is an initial over-current pulse during which the transport current was turned on rapidly, rising to 900A during the first milliseconds, then reduced to a 100A DC current. The second start-up scenario is normal operation, and involved increasing the transport current slowly from 0A to 100A at a rate of 1A/s. For both scenarios, we then measured the vertical component of the self-magnetic field by means of a Hall probe above the tape, and afterward, by solving a linear equation of the inverse problem we obtain the current density profiles. We observe a change of the self-magnetic field above the edge of the BSCCO and YBCO tapes during 30min after the 5ms of over-current pulse and during the normal operation. The current density profiles are peaked in the centre for over-current pulse, and more peaked around the edge of the HTS tape for normal operation, which means that the limited time over-current pulse changes the current density profiles of the HTS tapes. We observe also a loop of current for YBCO tapes and we show the role of the HTS tape stabilizer.