ABB Relion 650 Series Technical Manual page 554

Section 16
Basic IED functions
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
Optional synchronization of
modules at a lower level
IEC09000342 V1 EN-US
Figure 287: 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,
which give 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.
16.3.8.2 Real-time clock (RTC) 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 will
provide 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 will be lost completely.
Real-time clock at startup
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 directly for
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a higher level
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Function
IEC09000342-1-en.vsd
1MRK 506 326-UUS B
M11346-83 v2
M11346-57 v2
M11346-60 v2
M11346-63 v2
M11346-66 v4
Line distance protection REL650
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