Comparing Electrodynamic Losses During Transport Current Cycles in Insulated and Non-Insulated HTS Coils

Abstract

So far, the No-insulation (NI) technology using High Temperature Superconducting (HTS) materials has been limited to magnetic and power devices involving slow charging rates, generally avoiding AC applications, due to the onset of transverse currents. However, the limits of applicability are not well defined and few quantitative comparisons between insulated and NI coils under time-varying regimes have been presented. A proper analysis of the AC losses under these conditions is important to assess the possible use of NI windings for fast-charging or AC devices. This paper focuses on the layer-wound configuration of NI coils, less studied in the literature than the pancake-wound configuration. The investigation aims at comparing the behavior of two coils wound from the same tape, with or without electrical insulation between turns. The two coils are characterized by a very similar geometry, with the same number of turns and layers. The AC losses are assessed by adopting appropriate experimental setups in two different laboratories. Charge-discharge tests are performed with different ramp-rates up to a peak current with a triangular or trapezoidal waveform, determining the electrodynamic losses during these current cycles. Furthermore, the windings are supplied with sinusoidal currents of different amplitude and frequency, pointing out the differences in terms of AC losses between the two coil configurations.