Impact of Core Air-Gap Design on Electromagnetic Behavior and Loss Performance in High-Temperature Superconducting Transformer

Introducing air gaps into the magnetic core of high-temperature superconducting (HTS) transformers can help mitigate magnetic saturation to some extent and influence both electromagnetic performance and losses. To investigate this effect in detail, this article develops a 3-D finite element model of a 9 kVA three-phase HTS transformer. The study examines how variations in air-gap length and position affect the main magnetic flux path, leakage field distribution, and associated losses. The results show that increasing the air-gap length effectively alleviates local magnetic saturation in the core, resulting in a significant reduction in core loss. However, this also leads to a notable increase in leakage field intensity near the gap edges. When the air-gap percentage increases from 0% to below 6%, the ac loss remains under 100 W; beyond 8%, the ac loss rises sharply. Furthermore, placing the air gap at the center of the core limb minimizes both ac loss and core loss. These findings offer theoretical support for optimizing core air-gap design in HTS transformers to improve electromagnetic performance and suppress energy loss.