21.12.2.3 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.21.12.2.4 Time synchronization for differential protection and IEC/UCA61850-9-2LE sampled data GUID-413328FC-47E2-499B-8E11-AD51EF1B525A v4When using differential communication in conjunction with sampled data receivedfrom merging units (MU) over the IEC/UCA 61850-9-2LE process bus, the MUand the IED needs to be controlled by the same GPS synchronized clock. Therequired accuracy is +/- 4 μs. The accuracy can be achieved by using a GTM, GPS-based IRIG-B clock or PTP clock, and synchronizing MU from the same clock orfrom the PPS output of the GTM card. If, for instance, IRIG-B is used, the settingsfor time synchronization should be CourseSyncSrc = Off, FineSyncSource = IRIG-B, TimeAdjustRate = Fast. The setting for Encoding in SYNCHIRIG-B needs to beset to 1344.1MRK 505 393-UEN B Section 21Basic IED functionsLine differential protection RED650 2.2 IEC 421Application manual
