Preliminary Experimental Investigation of Graded Insulation on the Performance of HTS Pancake Coils

This work investigates a preliminary implementation of the ‘graded approach’ to the transverse resistance in HTS pancake coils. This method aims to find an optimal winding approach by combining key advantages of the no-insulation (NI) and metal-insulation (MI) coils in terms of operation stability and dynamic response, through a sectional variation of the insulation level. Unlike previously reported Partial Insulation (PI) approaches, this method does not rely on a regular insulation pattern throughout the entire winding but rather allows for targeted insulation placement based on qualitative criteria. Three pancake coils were realized and tested: an NI coil, an MI coil, and a graded-insulation (GI) coil with sectionally varied stainless steel tape layers to modulate transverse resistance. All coils were tested under the same conditions in liquid nitrogen, undergoing variable current ram…