ABB Relion 670 series, Technical Reference Manual

Page: 90 / 1232

4.3 Time synchronization
4.3.1 Introduction
The time synchronization source selector is used to select a common source of absolute
time for the IED when it is a part of a protection system. This makes it possible to
compare event and disturbance data between all IEDs in a station automation system.
A common source shall be used for IED and merging unit when IEC 61850-9-2LE
process bus communication is used.
Micro SCADA OPC server should not be used as a time
synchronization source.
4.3.2 Principle of operation
4.3.2.1 General concepts
Time definitions
The error of a clock is the difference between the actual time of the clock, and the time
the clock is intended to have. Clock accuracy indicates the increase in error, that is, the
time gained or lost by the clock. A disciplined clock knows its own faults and tries to
compensate for them.
Design of the time system (clock synchronization)
The time system is based on a software clock, which can be adjusted from external
time sources and a hardware clock. The protection and control modules will be timed
from a hardware clock, which runs independently from the software clock. See figure
25
Section 4
1MRK505222-UUS C
Basic IED functions
84
Technical reference manual