Thermal behavior of 2G HTS tape for use in resistive fault current limiters

Abstract

To design a commutative resistive fault current limiter it is important to study load characteristics of a superconducting tape as a non-linear resistive element. We used 2G HTS tapes SF12050 and SF12100 produced by Superpower Co. of 12 mm in width and of 50 and 100 μm in thickness, respectively. The tapes of different length in the range of 10 – 50 cm were studied. A loading current was a 10 ms half-sine pulse of different amplitude up to 1 kA. The pulse was generated using a low and high-voltage LC oscillatory circuit with frequency of 50 Hz. The HTS tape was immersed in liquid N2 (LN2). The temporal dependence of current through the tape and the voltage drop were measured simultaneously. The temporal dependence of the Joule losses and resistance of the tape were computed. The instantaneous values of the tape temperature during and after the loading period were determined. Three cases of the tape arrangement have been studied: (i) a single (isolated) tape, (ii) a bifilar tape, and (iii) a tape placed between two silicon plates. The tape temperature rise during the loading period is shown to govern the energy equation for the adiabatic case. The difference in thermal behavior of these systems is discussed. The cases (i) and (iii) differ from (ii) for relatively low loads. The cooling process is similar for cases (i) and (ii), i.e. the cooling rate is determined by different modes of LN2 boiling curve (film, transition, and nucleate boiling). A method is developed to calculate the cooling curve of the HTS tape immersed in LN2 after the end of current pulse using a steady-state boiling curve of LN2 corrected only for transition boiling mode. The silicon plates are found to promote a cooling process significantly.