Operating Performance of the Flux-Lock and the Transformer Type Superconducting Fault Current Limiter Using the YBCO Thin Films

The operating characteristics of the flux-lock and the transformer type superconducting fault current limiters (SFCLs) have been tested and compared each other. The SFCLs are composed of the primary and secondary coils and the YBCO thin film as a current limiting unit. The turn ratios between the primary and secondary windings were 63:21 and 63:42, respectively. The winding direction between the primary and secondary windings was subtractive. When a fault occurred under the same conditions, the line current was limited more effectively in the transformer type SFCL. That is, the current value of the flux-lock type SFCL was approximately 2 times as high as that of the transformer type SFCL at the turn ratio of 63:42. However, the flux flowing into the iron core of the flux-lock type was less saturated than in the transformer type due to its flux distribution. The resistance generated in the YBCO thin film was higher in the flux-lock type where its voltage was also higher because of the winding direction between the primary and secondary windings. The initial limiting current of the flux-lock type was 2 times as high as that of the transformer type at the turn ratio of 63:42. The power consumed in the YBCO thin film of the transformer type was also remarkably low because the resistance, the current, and the voltage of the YBCO thin film are all lower. Consequently, we found that the transformer type had advantages for the current limiting effect and power burden of the YBCO thin film.