Quench behavior of YBaCuO films for fault current limiters under magnetic field

The resistive superconducting fault current limiters (SFCLs) are very attractive devices for the electric power network. But they have some serious problems when the YBCO thin films were used for the current limiting materials due to the inhomogeneities caused by manufacturing process. When the YBCO films have some inhomogeneities, simultaneous quenches are difficult to achieve when the fault current limiting units are connected in series for increasing operating voltage ratings. In order to solve these problems, vertical magnetic fields varied from 0 to 130 mT were applied to the YBCO elements. Then, extensive electric field-current (E-I) and quench characteristics were investigated for all elements by using both electrical measuring method and observations of bubble behaviors. The experimental results were compared with the quench properties of YBCO elements, which were connected in series. From the experiment works, it was revealed that applied magnetic fields generated by surrounding coils could induce uniform quench distribution for all strips and simultaneous quenches were realized in all YBCO elements. Finally, by applying vertical magnetic fields perpendicular to the limiting devices, 1.2 kV_rms rated resistive fault current limiter were realized using five YBCO films in series.