Turn-to-Turn Contact Resistance Measurement of NI REBCO Double Pancake Coils

The turn-to-turn contact resistance/resistivity is one of the most important parameters for no-insulation (NI) rare-earth barium copper oxide (REBCO) pancake coils. Our group has been working on the measurement of the contact resistances of NI REBCO pancake coils by alternating current, called a low-frequency ac current (LFAC) method. One of the advantages is that the LFAC method is able to measure the field and current dependencies on contact resistances in principle, while the conventional discharge method is not. The effectiveness of the LFAC method was well demonstrated using a single pancake coil. In this paper, contact resistances of a double pancake coil were measured with the LFAC method although the upper and lower pancake coils had different turn-to-turn contact conditions due to an accident. The experiment results well agree with the simulation results. In addition, the contact resistances of each pancake coil can be separately specified. The contact resistances measured with a conventional sudden discharge method also have a good agreement with the LFAC method; however, the contact resistance of sudden discharge simulation is underestimated. Meanwhile, the energy consumptions are also complicated. We need further investigation for multi-stacked NI pancake coils in the near future.