High Reliability Selective Interlock System for Fault Protection of Critical Power Installations

This paper addresses selective coordination of protections in Low Voltage critical power electrical installations. We describe a digital interlock system, developed for MV/LV power distribution in critical power facilities, with the presence of multiple power generators, including the case of meshed distribution networks. A ship is considered as a case study, with MV/LV stations operated as a closed loop, and about 20MW total loads. Ethernet links are used for connection between protective devices in each switchboard. A redundant optical fiber link based on a fast-recovery ring structure is used for connection among switchboards. This architecture allows seamless data exchange between Medium Voltage protection relays and Low Voltage circuit breakers placed in the same or in different locations in the plant. Selective interlocking is ensured even in the case one of the optical links is lost. Immunity to EM noise is also improved. Before deployment in a real installation, the designed system has been reproduced in a Hardware-In-the-Loop environment, which allows the simulation of test cases including electrical faults in each location of the plant, failure of communication devices and links, or a combination of them at different times.