Method and system for calculating a fault indicator indicating a fault in a distribution network

An embodiment of the invention relates to a system (10) for calculating a fault indicator indicating a fault in a distribution network that comprises network sections with different phase numbers, said network sections being separated by at least one phase transition node. The system (10) is characterized by a computer (11) being programmed to carry out the steps of: forming Fortescue-π-Equivalents for every branch element of the distribution network and every phase transition node of the distribution network, determining a system admittance Fortescue matrix ( Y F ) based on said Fortescue-π- Equivalents, and calculating said fault indicator based on said admittance Fortescue matrix.