20.6.3 Operation principle20.6.3.1 General conceptsTime definitionsThe error of a clock is the difference between the actual time of the clock, and the time theclock is intended to have. Clock accuracy indicates the increase in error, that is, the timegained or lost by the clock. A disciplined clock knows its own faults and tries tocompensate for them.Design of the time system (clock synchronization)The time system is based on a software clock, adjustable from external time sources, andon a hardware clock. The protection and control modules will be timed from the hardwareclock which is synchronized with the software clock. See figure 272SW-timeTime-RegulatorTime tagging and general synchronisationTime-Regulator(Setting, seetechnicalreferencemanual)Comm-unication EventsSynchronization for differential protection(ECHO-mode or GPS)Diff.-comm-unication*IEC 61850-9-2IEC140000113-1-en.vsdExternalSynchronizationsourcesTrans-ducers*GPSIRIG-BOffProtectionand controlfunctionsA/DconverterHW-timeIEC140000113 V1 ENFigure 272: Design of the time system (clock synchronization)All time tagging is performed by the software clock. When, for example, a status signal ischanged in the protection system of a function based on the free running hardware clock,the event is time tagged by the software clock when it reaches the event recorder.1MRK 511 365-UUS A Section 20Basic IED functionsPhasor measurement unit RES670 2.1 ANSI 719Technical manual
