Protection Coordination for Reliable Marine DC Power Distribution Networks

This paper presents demonstration of a protection scheme integrated into marine DC power distribution networks to investigate the coordination between each protection action. The integrated protection scheme is based on three different time-frame protection actions: fast action - bus separation by a solid-state bus-tie switch, medium action - feeder protection by high-speed fuses, and slow action - power supply protection by generator deexcitation. As the backup protection of the power supply protection, AC fuses are installed between generators and rectifiers. To coordinate each protection action, the influences of the inductance in the bus-tie switch and the DC-link capacitance are investigated by DC short-circuit tests with the different inductance and capacitance values. The protection scheme, coordinated by the above investigation, is verified by system-level short-circuit tests for bus and feeder faults. To validate the protection scheme for various fault conditions, low- and high-impedance fault currents are analytically calculated for the bus faults and simulated for the feeder faults. Time-current curve analyses show that the coordinated protection scheme can effectively protect marine two-bus DC power distribution networks with correct operations of the protection measures and enough time margins between the different actions.