  This paper introduces an algorithm able to detect and localize the occurrance
of a fault in an Active Distribution Network, using the measurements collected
by Phasor Measurement Units (PMUs). First, a basic algorithm that works under
the assumption that all grid buses are equipped with a PMU is designed. Then,
formal observability conditions that allow detection and localization with a
reduced number of PMUs are provided. Based on these conditions, the algorithm
is extended to perform correctly when not all network buses are monitored.
Moreover, an Optimal Positioning Algorithm, always based on the observability
conditions, is designed. This algorithm allows the user to customize the fault
localization resolution. The approach is validated through simulations carried
out on a benchmark active distribution network.
