SmpSynch, holdover and the fate of complex protections at a digital substation
What IEC 61869-9 actually requires, and where the boundary lies between "still synchronized" and "no longer synchronized". The article unpacks the "2 → 1 → 0" misconception about SAMU/NCIT behavior on PTP loss, the link between clockClass, timeTraceable and SmpSynch, and how a complex protection function should react when one of its source streams loses synchronization.