3.5
Time synchronization
3.5.1
Functionality
The protection relay has an internal real-time clock which can be either free-running or
synchronized from an external source. The real-time clock is used for time stamping
events, recorded data and disturbance recordings.
The protection relay is provided with a 48 hour capacitor backup that enables the real-time
clock to keep time in case of an auxiliary power failure.
The setting
Synch source
determines the method to synchronize the real-time clock. If it
is set to “None”, the clock is free-running and the settings
Date
and
Time
can be used to
set the time manually. Other setting values activate a communication protocol that
provides the time synchronization. Only one synchronization method can be active at a
time but SNTP provides time master redundancy.
The protection relay supports SNTP, IRIG-B, DNP3 and Modbus to update the real-time
clock. IRIG-B with GPS provides the best accuracy.
When Modbus TCP or DNP3 over TCP/IP is used, SNTP time
synchronization should be used for better synchronization accuracy.
DNP3 can be used as a time synchronization source.
When the SNTP server IP setting is changed, the protection relay must be
rebooted to activate the new IP address. The SNTP server IP settings are
normally defined in the engineering phase via the SCL file.
The relay can use one of two SNTP servers, the primary or the secondary server. The
primary server is mainly in use, whereas the secondary server is used if the primary server
cannot be reached. While using the secondary SNTP server, the relay tries to switch back
to the primary server on every third SNTP request attempt. If both the SNTP servers are
offline, event time stamps have the time invalid status. The time is requested from the
SNTP server every 60 seconds.
IRIG-B time synchronization requires the IRIG-B format B004/B005 according to the
200-04 IRIG-B standard. Older IRIG-B standards refer to these as B000/B001 with
IEEE-1344 extensions. The synchronization time can be either UTC time or local time. As
Section 3
1MRS240050-IB C
Basic functions
64
REF615R
Technical Manual
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