Normal zone propagation in 2-dimensional YBCO winding pack models

This paper presents the results of a study of 2-dimensional normal zone propagation (NZP) in winding pack models comprised of 12 straight YBCO tapes stacked with wet, i.e., epoxied, insulating spacers. In each winding pack, the YBCO tapes were connected electrically in series in such a way that a transport current through the YBCO tapes zigzagged from one end of the winding pack to the other end of the winding pack. An insulated heater strip placed at the middle of the stack was energized to trigger a quench in YBCO tapes with a combination of heater taps which permits the length of the heated section to be varied for 1- or 2-dimensional NZP. Voltage taps of various lengths were placed within the winding packs to measure the transverse and longitudinal NZP speeds. Measurements with wet-spacers in which a large contact thermal resistance at each YBCO tape and spacer interface is chiefly responsible for very slow transverse NZP velocities, effectively eliminate the interface thermal resistance, resulting in faster transverse NZP. speeds. Numerical simulation that neglects interface thermal resistance agrees quite well with experiment.