In power system state estimation, similar to power flow, an angular reference is required in order to solve the problem providing the most likely state of the system. For single-phase state estimators (SEs), the usual practice is to specify the angular reference at the substation bus, usually at 0 degrees. This study discusses and presents how to specify the angular reference for three-phase distribution systems SEs (DSSEs). As the main contributions, two different approaches for specifying the reference are presented and assessed. Additionally, the more general proposed approach is improved and a robust version, based on a reduced number of state variables, is presented. The proposed approaches are applied to three SEs commonly recommended for distribution systems. The results show that the approach based on a reduced number of state variables is a proper and general solution to specify the reference angles for three-phase DSSEs Ver menos