Magnetic AC loss in twisted-filament Bi-2223 tapes

In AC power-engineering applications, the energy dissipation in tie superco nductor is dominated by the magnetization due to alternating fields. To red uce this type of loss, conductors are being developed with twisted filament s and an increased matrix resistivity. The magnetic AC loss has been well d escribed for low-T-c (wire) conductors. In Bi-2223 tapes the picture is dif ferent due to strong anisotropy, granularity, flux creep and large aspect r atio of the tape. The magnetic AC loss is investigated at power frequencies in various Bi-2223 tapes (twisted and non-twisted) and with different mate rials for the matrix (Ag, Ag alloys and ceramic barriers), When the field i s parallel to the tape plane, the filaments in twisted tapes can be decoupl ed and the AC loss is decreased even when the matrix is silver. In tapes wi th ceramic barriers between the filaments, first indications of filament de coupling are observed also in perpendicular field. Compared to a round wire , there are essential differences between the AC loss mechanisms occurring in a long twisted tape and those in a short piece of non-twisted tape.