Speaker
Description
The no-insulation (NI) winding technique improves the thermal stability of REBCO pancake coils. A radial bypass current protects an NI pancake coil from burning-out when it turns a normal state. That is, the characteristic resistance (turn-to-turn contact resistance) of NI REBCO pancake coil characterizes the electrical behavior inside the coil as a function of “self-protecting.” To estimate or predict the thermal stability, the characteristic resistances are measured through a sudden discharging test. The sudden discharging test estimates the characteristic resistance from a measured time constant and a calculated coil inductance. However, it is well known that the characteristic resistance varies depending on the temperature, the current, and the magnetic field (i.e. stress condition). It is hard to measure the changing characteristic resistance under different conditions by means of the sudden discharging test.
We have recently developed a characteristic resistance measurement method using an AC current. The developed AC-current method easily measured a characteristic resistance under zero magnetic field and zero DC transport current. As a next step, we tried to measure the characteristic resistances of NI REBCO pancake coil under different temperatures or DC operating currents. The dependency of the characteristic on the temperature and transport current is very useful information to know the electromagnetic behaviors inside NI REBCO pancake coils.
