Non-telecommunication based DC line fault detection methodology for meshed HVDC grids

One of the most challenging aspects regarding realization of meshed HVDC systems are DC line faults. On the one hand new fault clearing equipment needs to be developed. On the other hand it is very important to define suitable fault detection methods. This is necessary since proven methods for AC grids cannot be applied in DC grids since they are too slow to cope with DC fault current phenomena. To clear DC faults it is important to have fast acting fault clearing but at least equally important to have very fast fault detection. For time critical and economical reasons it is also required to have a decentralized fault detection method. This paper describes basically DC fault current calculation, shows typical HVDC fault current characteristics and proposes an appropriate DC fault detection methodology for pole to pole as well as for pole to earth (in low- and high-impedance earthed DC grids) faults. Finally this fault detection algorithm is validated by numerical case studies.