ABB Relion RES670, Technical Manual

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been reached. The protection function is then enabled and the synchronization remains
in fast mode or switches to slow mode depending on the setting.
Synchronization principle
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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.
Function
Synchronization from
a higher level
Optional synchronization of
modules at a lower level
IEC09000342-1-en.vsd
IEC09000342 V1 EN-US
Figure 294: 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 based on 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.
22.1.3.2 Real-time clock (RTC) operation
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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 2100.
Real-time clock at power off
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During power off, the system time in the IED is kept by a capacitor-backed real-time
clock that will provide 5 ppm accuracy for at least two days. This means that if the
Section 22
1MRK 511 408-UUS A
Basic IED functions
768 Phasor measurement unit RES670 2.2 ANSI
Technical manual