Influence of the conductor’s arrangement and current on the AC loss characteristics of a fault current limiting coil

Abstract

Researches and developments on a superconducting fault current limiting (SFCL) system have been done for several decades. The SFCL system, which is using a high temperature superconducting (HTS) conductor such as Bi-2212 bulk and YBCO film, has recently become technically available. In this work, we are developing a 22.9 kV/25 MVA SFCL system for a power distribution network. A Bi-2212 bulk SFCL element, which has the merits of large current capacity and high allowable electric field during fault of the power network, becomes a candidate for our resistive SFCL system. AC loss of the HTS conductor has a strong influence on the economic viability of the SFCL system, which offers an attractive means to limit short circuit current in the power network. As an earlier stage of our 22.9 kV/25 MVA SFCL system development, we prepared several samples of the fault current limiting elements in a coil shape to reduce AC loss of the SFCL system. The effect of conductor’s arrangement and current direction on AC loss characteristics of the fault current limiting coils has been investigated experimentally. The test result shows that the measured AC loss depends significantly on the conductor’s arrangement and also on the current direction even in the same arrangement. The AC loss of a face-to-face coil in bifilar mode, which is even smaller than the self-field loss of the conductor, is smallest among our fabricated coil samples. Moreover, the measured loss in the face-to-face coil in bifilar mode is invariable regardless of thickness in an insulator which is placed between conductors.