Non-destructive Detection of Normal Transitions in High Temperature Superconducting Coil

Abstract

High temperature superconducting (HTS) coils require reliable quench monitoring systems for safety operations. Also, locating of normal transition areas is important for developing reliable HTS coils. Resistive voltage measurement method is universally used for the quench detection and the location. The method needs many voltage taps soldered to superconducting windings and therefore insulations of superconducting wires have to be removed for the soldering and then it has high risks in terms of high voltage sparks. In this paper, the authors present a new detection method of normal transitions by using capacitor taps which can detect normal transitions regardless of the insulations (by no destruction) and has no risks about the high voltage sparks. In this method, two electro-conductive sheets are attached on a surface of a superconducting coil and are connected with an outside capacitor. Then two capacitors are created on the surface of the superconducting coil by sand iching the insulation between each electro-conductive sheet and the superconducting wire. The normal transitions can be detected as a voltage of the outside capacitor by voltage dividing with the three capacitors. A demonstration test was carried out for a Bi2223 coil and the quench detection and the location were successfully achieved.