Study on the electrical contact resistance properties with various winding torques for noninsulated HTS coils

In the case of motors and generators, the benefits of using high-temperature superconducting (HTS) coils can be represented by the reduction of 50% in both losses and sizes compared to conventional machines. However, it is hard to establish quench detection and protection devices for the HTS coils applied to the rotors of motors and generators. Therefore, the stability of the coils is lower than for the quiescent coils applied to NMR, MRI, and so on. Therefore, it is important to improve the self-protection ability of HTS coils. We have studied the methods to improve the self-protection ability of HTS coils by removing the turn-to-turn insulation and inserting metal tape instead of the electrical insulation. When the coils are energized, there are voltages generated by sweep rate of the current (di/dt) and inductance of the coil. Because noninsulated HTS coils have electrical contacts along the transverse direction, a bypass current is generated along the transverse direction and noninsulated HTS coils have a risk of Joule heating in the stabilizer and metal substrate. Furthermore, the electrical contact resistance of noninsulated HTS coils was changed by a winding torque. In this paper, we measured the electrical contact resistance along the transverse direction with various winding torques for noninsulated HTS coils.