Real-Time Clock (Rtc) Operation - ABB Relion 670 Series RES670 Technical Manual

Section 20
Basic IED functions
20.6.3.2
720
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 273: 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.

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.
Function
IEC09000342-1-en.vsd
Phasor measurement unit RES670 2.1 ANSI
1MRK 511 365-UUS A
Technical manual