ABB Relion 630 Series, Technical Manual

Page: 109 / 380

Function
Synchronization from
a higher level
Optional synchronization of
modules at a lower level
IEC09000342-1-en.vsd
IEC09000342 V1 EN
Figure 53: 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 in three ways.
• 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
3.16.8.1 Real-time clock operation
The IED has a built-in real-time clock (RTC) with a resolution of one second. The
clock has a built-in calendar that handles leap years through 2038.
Real-time clock at power off
During power off, the system time in the IED is kept by a capacitor-backed real-time
clock that provides 35 ppm accuracy for 5 days. This means that if the power is off, the
time in the IED may drift with 3 seconds per day, during 5 days, and after this time the
time is lost completely.
Time synchronization startup procedure
The first message that contains the full time (as for instance SNTP and IRIG-B) gives
an accurate time to the IED. The IED is brought into a safe state and the time is set to
the correct value. After the initial setting of the clock, one of three things happens with
each of the coming synchronization messages, configured as “fine”.
• If the synchronization message, which is similar to the other messages, from its
origin has an offset compared to the internal time in the IED, the message is used
1MRS757256 F
Section 3
Basic functions
PML630/Compact Load-Shedding Solution 103
Technical Manual