Protection system design for low voltage direct current networks

Direct current networks will be an important backbone of future energy supply and distribution. However, many challenges still need to be overcome especially in the field of DC protection. Well-developed DC protection systems that provide effective and selective protection are required. In this work, a modular and algorithm-based protection system is developed and analysed. For the determination of useful DC protection criteria, tests are performed using various load changes within a DC model network. The found criteria will be used for the development of a novel protection concept using event detection, characterisation, localisation, and selective switch off algorithms. For these algorithms, the transient phenomena within the DC network at load change will be analysed by sampling and processing of current- and voltage signals from sensor-equipped switching units distributed at specific locations within the DC network. Furthermore, it consists of an embedded-system-based protection unit to evaluate the network status in real time and executes the right decision based on the processed data in the event of a transient phenomenon to ensure reliability of supply. The reliability, speed and selectivity of the protection system have been validated in different network topologies. In all cases, the tested overload and short circuit cases have been reliably detected and – only if necessary – switched off successfully. Furthermore, uncritical transient overload cases did not lead to unnecessary interruption by the protection system. The proposed protection system thus represents a flexible, expandable, and effective way of protecting DC networks. With this developed approach, only a simplified analysis of the network conditions and components is required to ensure an effective protection.