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The high temperature superconducting (HTS) coils have very low normal zone propagation velocity (NZPV) and complicated quench behaviors. Because of these reasons, it is difficult to expect the self-protection. In this paper, two methods are suggested to improve the self-protection ability of HTS coils. One is to remove the insulation between turn–turn winding in HTS coils to enhance the thermal and electrical contacts along transverse direction and to increase the whole thermal stability of them. The other is Cu or Brass tapes are wound with HTS tape wire instead of the insulation to improve the thermal, electrical and mechanical stability of the HTS coils. To clarify the quench behaviors of the suggested coils, the normal zone propagation properties of the fabricated non-insulated HTS pancake coils were shown by measured voltage and temperature traces during the quench as a function of the operating temperature. And the characteristics of the normal transition and amount of the shared current to adjacent layers were quantitatively measured by a Hall sensor located at the center of HTS coils to measure the change of the self-magnetic field by operating current. The current sharing behaviors in the non-insulated HTS coil and the coil with Cu tape inserted were observed. The minimum quench energy (MQE) of the HTS coil with Cu tape inserted was the largest in the tested coils. It means that the HTS coil with Cu tape inserted had the highest transient stability against the thermal disturbances among the tested coils and the improvement of self protection abilities was proved.

The resistive type fault current limiter based on YBCO thin film with high critical current density was proposed and developed because of its fast recovery characteristics. We have been developing a magnetic field measurement system with hall sensor to study the critical current density distribution or magnetic properties of high-Tc superconductors such as thin film, tape conductor and coated conductors. In this study, the transport current distribution in straight line and U-corner region of meander type resistive fault current limiter using YBCO thin film was investigated experimentally. The both axial and radial self-magnetic field components according to the direct (DC) and alternating (AC) transport currents were measured by two-axis hall probe to estimate the current distribution. And also, the self-magnetic field at the corner of bispiral type fault current limiter was measured by two-axis hall probe with a high spatial resolution to compare with the meander type fault current limiter.

Single-, multi-, and two kinds of coaxial-filament composite MgB 2 /SS–SS (stainless steel for both outer and inner tubes) and MgB 2 /SS–Cu (stainless steel for outer tube and copper for inner tube) wires were successfully fabricated using powder-in-tube (PIT) process with swaging only. The effect of the geometries of the MgB 2 PIT wires has been studied comparatively. The isothermal magnetizations M ( H ) for both the sintered and the as-rolled single-, multi-, and coaxial-filament MgB 2 wires were measured at temperatures between 5 and 50 K in fields up to 5 T. The critical current density was estimated by the M ( H ) data using Bean model. The coaxial-filament composite MgB 2 wires showed much better J c than both the single- and the multi-filament composite ones. The results of this study show that the superconducting properties of the MgB 2 PIT wires/tapes can improve by employing better geometries such as the coaxial-filament composite MgB 2 /SS–SS wires.