via a PPS out from the GTM. If PTP is used in the IED and the merging unitcannot be synchronized from the IED, then use GPS-based clocks to provide PTPsynch 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 either PMU or LDCM in GPS-mode isused, that is, the hardware and software clocks are connected to each other,HwSyncSrc is not used and other means to synchronize the merging unit to the IEDis required. Either FineSyncSource is set to the same source that the merging unituses, or the PPS output from the GTM module is used to synchronize the mergingunit. If the PPS output from the GTM module is used to synchronize the mergingunit and PTP is not used, the IED does not know how the merging unit issynchronized and the parameter LostSyncMode must be set to NoBlock.1MRK 506 369-UEN B Section 24Basic IED functionsLine distance protection REL670 2.2 IEC 875Application manual
