ABB RET650 Technical Manual page 574

Section 17
Basic IED functions
568
External
synchronization
sources
Off
SNTP
IRIG-B
DNP
IEC60870-5-103
IEC09000210 V2 EN
Figure 252: Design of time system (clock synchronization)
All time tagging is performed by the "software" clock. When for example a status
signal is changed in the protection system with the function based on "free
running" hardware clock, the event is time tagged by the software clock when it
reaches the event recorder. Thus the "hardware" clock can run independently.
Synchronization principle
From a general point of view synchronization can be seen as a hierarchical structure.
A function is synchronized from a higher level and provides synchronization to lower
levels.
Synchronization from
a higher level
Optional synchronization of
modules at a lower level
IEC09000342 V1 EN
Figure 253: Synchronization principle
A function is said to be synchronized when it periodically receives synchronization
messages from a higher level. As the level decreases, the accuracy of the
synchronization decreases as well. A function can have several potential sources of
synchronization, with different maximum errors. This gives the function the
possibility to choose the source with the best quality, and to adjust its internal clock
after this source. The maximum error of a clock can be defined as:
Time tagging and general synchronization
Commu
- nication
Time-
regulator
SW- time
Function
IEC09000342-1-en.vsd
1MRK 504 135-UEN A
Protection
Events
and control
functions
IEC09000210-2-en.vsd
Technical manual