Superconducting Fault Current Limiter for Ship Grid Simulation and Demonstration

The strong growth of electrical power on ships leads to modifications and optimizations of their electrical grid, from their architecture to their components. An emerging architecture is the dc grid, which outperforms the ac solution. Security and protection are two major concerns on a ship. Even with controllable static converters, fault currents may be very high. For security reasons there are in general a port grid and a starboard grid. They are not connected in normal operation: a fault (short-circuit) on one grid must have no influence on the other grid to avoid a total blackout. On the other side, a coupling between the two grids brings many advantages through mutualisation and a stronger grid. This coupling is possible using a superconducting fault current limiter (SCFCL). A SCFCL between the two ship grids appears as a promising solution to take benefit of the coupling under normal operation and the decoupling under a fault case. Simulations have been carried out using EMTP-RV to study the operation and the advantages of such SCFCL implementation, with consequences in terms of safety in addition to protection. These simulations show that the healthy grid does not nearly see the short-circuited one. The voltage of the dc bus only experiences a little transient drop (lower than 10%), whereas the ac voltage supplies for the propulsion motors are not affected at all. A demonstrator has been developed. It uses SuperOx REBCO pancakes. The rating is 500 A-800 V at 77 K using two 12-mm-wide tapes in parallel. The design of the demonstrator, of its SC element (design of the REBCO tape shunt) in particular and preliminary tests are presented in ac conditions but at temperatures higher than 77 K to fit the laboratory limited testing capacities.