Abstract: In response to the protection requirements of high redundancy and fault tolerance for closed bustie medium voltage power systems in DP-2 or DP-3 class ships, a selective protection scheme that balances reliability and rapidity is proposed to solve the problem of fault isolation under single-point fault superimposed with hidden faults, ensuring that the power loss area does not exceed the maximum allowable failure range of the dynamic positioning system-typically one section of the medium-voltage main busbar. Based on the operational characteristics of closed bustie power systems, each section of the medium-voltage system is divided into four protection zones: generator, busbar, load feeder, and bustie cable. A two-tier protection scheme consisting of primary and backup protection is constructed through the coordination of differential protection and directional pilot protection. Based on the 6.6 kV closed bustie power system architecture of a typical DP-2 class ship, a hardware-in-the-loop (HIL) test platform including various types of integrated relay protection devices in one section of the main busbar and digital real-time simulation systems was built. Simulation tests were conducted in four types of areas with eight operating conditions including single point faults and superimposed hidden faults, testing the effectiveness of both primary and backup protections in each zone. The results showed that the protection system could operate correctly under various operating conditions with dynamic changes in fault current levels, verifying the coordination, reliability and rapidity of the proposed protection scheme.

Key words: closed bustie, selective protection, regional protection, hidden fault, hardware-in-the-loop