| Because Alternating Current (AC) losses of high temperature superconducting (HTS) tapes have direct effects on the efficiency and cost of HTS apparatus, and the long-term stability of HTS apparatus mainly depend on the stability of HTS tapes. The investigation of AC losses and stability of HTS tapes has always been one of the most important research branches of HTS applications.In this paper, the AC loss measurement system and the quench propagation measurement system of HTS tapes were reconstructed firstly. Then the AC losses and quench propagation characteristics of HTS tapes have been investigated on the above facilities.AC transport losses of Bi-2223/Ag tapes were measured in self and DC background field repeatedly, and the experiment results were compared with Norris theoretical results. In parallel DC magnetic field, AC transport losses of Bi-2223/Ag tapes were measured with different voltage taps shapes, and the influence of vibration on AC loss measurement was qualitative analyzed.AC transport losses of YBCO tapes with ferromagnetic substrates were measured in parallel and perpendicular DC magnetic fields respectively. The influence of ferromagnetic substrate on AC losses of YBCO coated conductor and the dependence of AC transport losses in YBCO coated conductor on magnetic field were analyzed. In addition, the impact of electromagnetic "history" of the sample on AC losses of YBCO coated conductor were discussed after the perpendicular DC field removed.In the aspect of quench propagation investigation, the minimum quench energy (MQE) and the quench propagation velocity (NZPV) were measured in different Bi-2223/Ag tapes with AC and direct current (DC) respectively. The influence of stabilized material on quench propagation characteristics of Bi-2223/Ag tapes was analyzed, and the quench behavior of Bi-2223/Ag tapes with AC and DC transport currents were compared. Then the MQE and the NZPV in YBCO tapes with AC and DC transport currents were measured and compared.
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