SDH-based time synchronous system for power system communications

As precise time information is particularly useful for power system communications, a time transfer system using terrestrial fiber optic digital networks, or SDH (Synchronous Digital Hierarchy)-based time synchronous networks, is proposed in addition to radio- or satellite-based time dissemination systems such as GPS (Global Positioning System). In the system, auxiliary time synchronizing equipment is attached to existing SDH networks composed of SDH transmission equipment and digital clock supplies, and not only frequency but also frame phase or time is synchronized. Experimental time synchronizing devices showed potentially satisfactory performance; synchronization errors between two devices were of the order of sub-microseconds.