Superconducting fault current limiter (SFCL) in the medium and high voltage grid

Superconducting fault current limiters (SFCLs) combine features not provided by conventional switching devices. In the medium voltage (MV) grid the installation of SFCLs as bus coupler and in the transformer feeders are of special interest. Thus the short circuit power can be increased without exceeding the admissible short circuit strength. In consequences higher loadings and perturbing custumers can be connected. In the high voltage (HV) grid an interesting application for SFCLs is the coupling of 110 kV sub-grids by which the surplus of transformer capacity can considerably be reduced. The reserve power is delivered by the other sub-grid, while the short-circuit current is limited to admissible values by SFCL. To prove the feasibility a 10 kV SFCL demonstrator was installed in a 10 kV substation. The fundamental design of the apparatus, the tests and the service experience are presented. In total the apparatus demonstrated a good long-term performance