Testing of machine wound second generation HTS tape Vacuum Pressure Impregnated coils

Abstract

Abstract. Delamination of second generation (2G) High Temperature Superconducting (HTS) tapes has previously been reported when using resin based insulation systems for wound coils. One proposed root cause is the differential thermal contraction between the coil former and the resin encapsulated coil turns resulting in the tape c-axis tensile stress being exceeded. Importantly, delamination results in unacceptable degradation of the superconductor critical current level. To mitigate the delamination risk and prove winding, jointing and Vacuum Pressure Impregnation (VPI) processes in the production of coils for superconducting rotating machines at GE Power Conversion two scaled trial coils have been wound and extensively tested. The coils are wound from 12mm wide 2G HTS tape supplied by AMSC onto stainless steel 'racetrack' coil formers. The coils are wound in two layers which include both in-line and layer-layer joints subject to in-process test. The resin insulation system chosen is VPI and oven cured. Tests included; insulation resistance, repeat quench and recovery of the superconductor, heat runs and measurement of n-value, before and after multiple thermal cycling between ambient and 35 Kelvin. No degradation of coil performance is evidenced.

Flux front dynamics and energy losses of magnetically anisotropic 2G-HTS pancake coils under prospective winding deformations

“…In this sense, greater misalignments are unlikely to happen as it is virtually improbable to evince a scenario where the imbalance between the positioning of the innermost and outermost turns of a laminar coil will be greater than half of its tape-width, unless the number of turns is much greater than 20. Nevertheless, it is worth mentioning that the threshold value for the misalignment factor, depends on the maximum width of the HTS tape that can be situated out of the collinear configuration (perfect winding), as long as it does not exhibit delamination behaviours, due to shear stresses between the different turns of the A c c e p t e d M a n u s c r i p t HTS coil [23], which could also be mitigated by the use of adequate insulation systems [24]. Hence, for the case of the SCS4050 tape that has been considered in this study, the maximum misalignment factor δ m = 1/10 is a plausible threshold value as this has been already demonstrated for up to a 5 − M P a applied stress level with a 8 × 3 mm width anvil, the shear stress at less than 0.25 mm from the tape edges results negligible [25].…”

Local electromagnetic properties and hysteresis losses in uniformly and non-uniformly wound superconducting racetrack coils

“…Attaining a clear understanding of the physical and designing parameters that might render to the minimization of AC losses in these systems is, by default, one of the most important subjects in the physics and engineering of applied superconductivity. [6][7][8][9][10][11][12] However, despite many experimental and theoretical studies have been performed on the AC losses of HTS racetrack coils, [13][14][15][16][17] these always assume that the coil is perfectly wound, neglecting thence any influence of a possible misalignment between the coil turns (tapes), a situation that is likely to happen either during the coil manufacturing, their assembling in practical applications, or even due to possible axial alterations caused by extrinsic magnetic, thermal, or mechanical pressure over the coil turns. In fact, despite than in the last two decades the applied superconductivity field has experienced a significant increase in the physical understanding of the local electromagnetic properties of type II superconductors, including the second generation of high temperature superconducting (2G-HTS) tapes, it is the high aspect ratio of the 2G-HTS tapes what from the computational perspective is still imposing significant challenges to understand their performance in practical superconducting machines.…”