Design principles and AC loss mitigation strategies for a 15 MVA HTS transformer

Offshore wind generators are expected to exceed 15 MVA in the coming years, necessitating compact and light-weight step-up transformers. While high-temperature superconducting (HTS) transformers offer high efficiency and compact size, their complex AC loss behavior in large-scale devices is still not sufficiently understood. In this work, we present a comprehensive investigation on practical strategies for reducing AC loss in a 15 MVA HTS transformer based on the primary industrial criteria of efficiency, weight, and cost. We employed an efficient numerical method to model up to thousands of HTS tapes in low-voltage (LV) and high-voltage (HV) windings in detail. Using this framework, we evaluated the influence of key design and operating parameters on the AC loss, including winding height, axial gap between the cables, radial distance between HV and LV windings, winding height difference, number of parallel conductors, voltage per turn, magnetic flux diverters, and temperature. These analyses enable the development of four improved transformer designs at operating temperatures of 20 K, 70 K, and two configurations at 77 K that balance AC loss reduction with conductor cost and core weight. The results provide validated design principles and practical guidelines for developing next-generation HTS transformers that are compact, light-weight, cost-effective, and suitable for large-scale offshore wind energy systems. • Numerical framework developed for AC loss evaluation in HTS transformers • Impact of key operating and design parameters on AC loss quantified • Reduction of AC loss at winding ends is identified as key design strategy • Design trade-offs between AC loss, conductor length, and cost are analyzed • Optimized HTS transformer designs proposed for 20 K, 70 K, and 77 K