The Research On AC Losses Of Bi-based High Temperature Superconducting Wires/Tapes

The alternating current (ac) losses of the applied high temperature superconductors (HTS) are dominating factors related to the stability and the cost of the HTS devices. The advantages of the HTS tapes/wires will be outstanding as long as the ac losses are low enough. Thus, it’s necessary to investigate the ac losses of the HTS hence explore reasonable approaches to the ac loss reduction.And in this experiment, a set of self-field losses measurement devices were firstly established for the HTS. Besides, the sources of the error were also analyzed for the error reduction in the measuring system. The experimental accuracy in the measurement achieves10-5Watt per meter.Then, the experimential samples for Bi2212round wires are fabricated by the powder in tube (PIT) method. Detailed analysis of V-I characters for the Bi-based HTS tapes carrying alternating current and the waveform observations of the loss voltage with different transport current and frequencies were carried on. It has been found that the Ⅴ-Ⅰ curves are nonlinear, and there exists a90°hase angle between the loss and the induction voltages. In addition, we also investigate the effect of the diameter sizes and the filament numbers of the Bi2212wires/tapes on the ac losses. And found that the ac losses get lower when the tape has more filaments and the wire diameter is finer. We also studied the self-field ac losses and characters with different frequencies of the parallel stacked tapes. The results indicated that when the frequencies and normalized current is fixed, the ac losses of the stacked tapes increase with the number of the stacked tapes. While the ac losses decrease with the number of the parallel strip only if the transport current and frequency is fixed.Finally, ac self-field losses of the Bi2223tapes with different critical currents were compared according to the Norris equation theory. The effects of the joint length on the critical current and ac losses of Bi2223tapes are briefly studied as well. The results show that the10-15mm common tape joints have a minimum influences on the degradation of the critical current. And the ac losses also decrease with the joint length of the Bi2223tapes which can be attributed to P=I2R as the joint resistance.