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

Section 17
Basic IED functions
17.2.8.2
674
• 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.
Real-time clock at startup
Time synchronization startup procedure
Coarse time synchronization is used to set the time on the very first message and if any
message has an offset of more than ten seconds. If no FineSyncSource is given, the
CoarseSyncSource is used to synchronize the time.
Fine time synchronization is used to set the time on the first message after a time reset or
if the source may always set the fine time, and the source gives a large offset towards the
IED time. After this, the time is used to synchronize the time after a spike filter, i.e. if the
source glitches momentarily or there is a momentary error, this is neglected.
FineSyncSource that may always set the time is only IRIG-B.
It is not recommended to use SNTP as both fine and coarse synchronization source, as
some clocks sometimes send out a bad message. For example, Arbiter clocks sometimes
send out a "zero-time message", which if SNTP is set as coarse synchronization source
(with or without SNTP as fine synchronization source) leads to a jump to "2036-02-07
06:28" and back. In all cases, except for demonstration, it is recommended to use SNTP
as FineSynchSource only.
Rate accuracy
In the IED, the rate accuracy at cold start is 100 ppm but if the IED is synchronized for a
while, the rate accuracy is approximately 1 ppm if the surrounding temperature is
constant. Normally, it takes 20 minutes to reach full accuracy.
Time-out on synchronization sources
All synchronization interfaces has a time-out and a configured interface must receive
time-messages regularly in order not to give an error signal (TSYNCERR). Normally, the
1MRK 502 048-UUS A
Technical manual