Standard superposition theorem has been the basis in the last decades for many power system problems decomposition involving changes in nodal injections, from productions and loads. Its application scope has however been limited to fixed grid topology and breaks as soon as a topology change happens in the grid. For instance, it cannot be applied to compute N-2 power flows simply from N-1 security analysis. Topological changes also become a flexibility used more and more frequently for congestion management. Studying the effect of combinatorial topological changes is hence of interest, but so far very computation intensive. In this paper, we propose an extension of the superposition theorem to varying grid topologies. We demonstrate it under the DC approximation for all topological changes, namely line disconnection and reconnection, bus splitting and merging. We finally apply it to two use cases related to the above mentioned, effectively extending its scope of application.
