Quench Protection of YBCO Coils: Co-Winding Detection Method and Limits to Hot-Spot Temperature

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A quench detection method of a high-temperature superconducting (HTS) coil using a cowinding method is studied. It is experimentally shown using a small YBCO test coil that the cowinding method is highly effective in canceling the inductive voltage component and can detect a quench occurring in an HTS coil with high sensitivity, compared with a commonly used bridge-balance method. An HTS coil is damaged by a quench when hot-spot temperature exceeds a certain threshold. The authors also experimentally investigated conditions to keep the hot-spot temperature of coils wound of YBCO tapes below a safe level, using the highly sensitive cowinding quench detection method.