This activity reports on the development of direct current (DC) systems in distribution networks. The proper operation of future multi-terminal and multilevel MVDC networks requires an adequate study of protection systems to cope with fault events and ensure continuity of service for the supplied consumers. As part of this research, analysis was conducted of the performance of a static fault current interrupting and limiting device with integrated surge damping function employed in a multi-terminal and multilevel MVDC network.

The first part of the report covers the preliminary analysis on the interaction between a tri-terminal MVDC network and the static protection devices in the face of a fault event; this analysis identified the critical issue of overvoltages occurring in the central node of the network at the instant of disconnection of the failed terminal.

This was followed by an in-depth study of the main strategies at the regulatory level for limiting the occurrence of surges in distribution and transmission networks; at the same time, the static limiting and interrupting device was redesigned with the introduction of the surge damping function. The off-line simulations made it possible to verify the operation of the device in both the limiting and interrupting phases, limiting the occurrence of surges even in the presence of multiple protection devices afferent to the same network node.

The study was concluded with the validation of the models through real-time simulations, in particular it was possible to confirm that the addition of new feeders and new connections, each with its own static devices, does not change the dynamics of the shunting surges on the existing portion of the network.
Future developments include Control Hardware In the Loop (CHIL) simulations of the models thus developed, as well as an analysis of the placement of such static network surge protection and limitation devices; the analysis will include operational scenarios different from those considered in this activity, varying the structure of the MVDC network itself, for example, by implementing a ‘ring’ connection of nodes instead of the already used ‘star’ connection.