15.1.3.4 Process bus IEC/UCA 61850-9-2LE synchronizationGUID-6E384BDB-5598-4108-99B4-0B4A4E1828B2 v4When process bus communication (IEC/UCA 61850-9-2LE protocol) is used, it isessential that the merging units are synchronized with the hardware time of the IED(see Technical manual, section Design of the time system (clock synchronization) ).To achieve this, PTP, PPS or IRIG-B can be used depending of the facilities of themerging unit.If the merging unit supports PTP, use PTP. If PTP is used in the IED and themerging unit cannot be synchronized from the IED, then use GPS-based clocks toprovide PTP synch as well as sync to the merging unit.If synchronization of the IED and the merging unit is based on GPS, set theparameter LostSyncMode to BlockOnLostUTC in order to provide a block ofprotection functions whenever the global common time is lost.If PTP is not used, use the same synchronization method for the HwSyncSrc as themerging unit provides. For instance, if the merging unit provides PPS assynchronization, use PPS as HwSyncSrc. If LDCM in GPS-mode is used, that is,the hardware and software clocks are connected to each other, HwSyncSrc is notused and other means to synchronize the merging unit to the IED is required. Forinstance, FineSyncSource is set to the same source that the merging unit uses.15.1.3.5 Precision Time Protocol (PTP) GUID-4F2B68B8-CCC8-4173-A644-D1674D3146F8 v2PTP according to IEEE 1588-2008 and specifically its profile IEC/IEEE 61850-9-3for power utility automation is a synchronization method that differs from SNTP,for instance, by providing much better accuracy and by being not predefined. Bynot predefined is meant that it is not mandatory to have a predefinedsynchronization tree, as the master (Grand Master) may shift.Consider instead PTP as a synchronization grouping, i.e. all devices connected tothe PTP group will be synchronized to the same source or, if there is no externalsource the group will at least maintain a common time. The group is synchronizedby connecting one or more “Grand Master” clocks to it. The clocks can be part ofthe devices in the group or be specialized synchronization devices, as for instance aGPS clock or similar. If several synchronization devices are connected to thegroup, the “Best Master Algorithm” in the PTP protocol will assure that only one isthe “Grand Master”. The IED can act as a synchronization device and supply anysynchronization source (like SNTP, SPA) as clock input, that will synchronize thewhole PTP group if there is no better source available in the group. The IED can beconnected to several groups and thereby connect them to each other, by acting as a“Boundary Clock”. If PTP is “On” on several Access Points, the IED connects theAccess Points via a boundary clock. If PTP is “On” on redundant Access Points,the IED acts as a “Transparent Clock”.In a network there may be variety of possible masters that are connected togetherwhere the masters by selection, using the priority of PTP (also called the BestMaster Algorithm, or BMC) to determine which of them that is the best master.Section 15 1MRK 511 424-UEN BBasic IED functions624 Bay control REC650 2.2 IECTechnical manual
