Time synchronization concerns in substation automation system

One of the main problems in mixing old and new IEC 61850 devices in the same substation automation system is related to the network-based time synchronization. The IEC61850 defines two different protocols for distributing time in Station and Process Bus: SNTP and IEEE1588 PTP. The two protocols have almost different time representations and synchronization schemes. When an old IEC61850 device with SNTP has to be integrated into new substations with PTP-compliant network infrastructure, time gateways may be required. The paper discusses the time synchronization concerns in a typical Substation Automation System and analyzes the performance of a compact Time Gateway; it is a transparent, two-ports, device which is inserted in the last network link between the switch and the end device. The tests have been carried out by means of an embedded prototype based on FPGA. The experimental results show the applicability of the Time Gateway concepts, giving useful hints on the trade off between synchronization accuracy and device complexity.