Quench behavior of conduction-cooledY Ba2Cu3O7−δ coated conductor pancake coils stabilized with brass or copper

Abstract

The quench behavior of conduction-cooledY Ba2Cu3O7−δ (YBCO) coated conductor pancake coils is reported. Two coils, one stabilized with copper andone with brass, are wound with 25 m of conductor and instrumented with a heater and a largenumber of voltage taps and thermocouples. The critical current, minimum quench energy (MQE)and two-dimensional normal zone propagation velocity (NZPV) are measured as a function ofI/Ic, whereI is the transportcurrent and Ic is the critical current. Although the non-uniform temperatureand self-field distributions within the coils result in a non-uniformIc, the heater is able to induce quenches with energies above the MQE and both longitudinaland transverse propagation velocities are measured. In both coils, the longitudinal NZPV (10–40 mm s − 1) is about one order of magnitude larger than the transverse NZPV (1–2 mm s − 1). Moreover, a comparison between the Cu-stabilized coil and a short, straightCu-stabilized sample shows that the one-dimensional longitudinal propagation in the shortsample is significantly faster than the longitudinal propagation in the coil. This is due totransverse heat conduction (transverse propagation) which reduces the temperaturegradients in the coil but also slows down the longitudinal propagation. Thus, designing aquench detection system based upon data from one-dimensional experiments may result inan unintended level of risk.