ABB REC650 Technical Manual page 560

Section 15
Basic IED functions
554
Design of the time system (clock synchronization)
External
synchronization
sources
Off
SNTP
IRIG-B
DNP
IEC60870-5-103
IEC09000210 V2 EN
Figure 266: Design of time system (clock synchronization)
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 267: 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:
• The maximum error of the last used synchronization message
• The time since the last used synchronization message
• The rate accuracy of the internal clock in the function.
Time tagging and general synchronization
Commu
- nication
Time-
regulator
SW- time
Function
IEC09000342-1-en.vsd
1MRK 511 287-UEN A
Protection
Events
and control
functions
IEC09000210-2-en.vsd
Technical manual