A Back-up protection strategy for future DC grids utilising travelling wave energy

The complex nature of future DC grids necessitate the need for protection algorithms which are reliable and fast in operation to prevent the converters from damage. Research has shown that non-unit based protection algorithms are ideal candidates for the primary protection of DC grids. However, a back-up protection scheme must be put in place in the event of failure of the primary protection system. This study presents a travelling wave-based back-up protection scheme for consideration in DC grids of the future. The technique utilises the ratio of the forward and backward travelling wave energy at the local and remote end relay terminals for fault identification. For an internal fault, this ratio is less than unity at both relay terminals whereas for an external fault, the ratio is less than unity at one terminal and greater than unity as the other terminal. Simulation results presented in this paper show shows the suitability of the proposed technique.