ABB RELION REX640 Technical Manual page 124

Basic functions
If one SNTP server is used, it is recommended to set
This disables the server redundancy scheme and prevents the IED from attempting
to access a non-existing secondary server.
The time is requested from the SNTP server every 60 seconds. Supported SNTP
versions are 3 and 4. SNTP requires a high-performance server to meet the
performance expectations.
IEEE 1588v2
The protection relay's 1588 precision time protocol synchronization complies with
the IEEE C37.238-2011 and IEC 61850-9-3 profiles, which are interoperable with
IEEE 1588 v2. The protection relay is an ordinary clock which can operate either
in slave-only and slave or master mode. According to the supported profiles, the
frame format used is IEEE 802.3 Ethernet frames with 0x88F7 Ethertype as the
communication service and the delay mechanism is P2P. For both profiles, the
TLVs required are included in the announce frame (IEEE C37.238-2011: Organization
extension and Alternate time offset indicator TLVs, IEC 61850-9-3: Alternate time
offset indicator TLV).
Time synchronization with IEEE 1588 v2 creates many possible scenarios since it
is a dynamic synchronization method whereby the current master is determined
with the BMC algorithm. GNRLLTMS outputs reflect this status. When IEEE 1588
v2 is used as a time synchronization source, the device stores the grandmasters
in priority order according to the BMC algorithm. When the grandmaster clock
is lost, an alarm and a warning are activated based on the stored grandmasters'
list. The alarm is activated when there are no clocks with capabilities equivalent
to primary or secondary grandmaster clocks. The warning is activated when a
primary grandmaster clock is not available. The grandmaster list can be Section 3
1MRS759142 E Basic functions 132 REX640 Technical Manual cleared using the
clock list setting, for example, if the grandmaster clocks need to be replaced. The
setting af-fects only the alarm and warning states.
If the current master is not within the 1 µs accuracy, ALARM is set to TRUE. If
the current master is not the saved primary master, WARNING is set to TRUE. The
EXTCLKMSTR output indicates if the ordinary clock is a slave to an external master.
Since the list is updated via the current primary master in the network, it is possible
to lower the current grandmaster's priority to a point where another clock takes
the role and the priority value in the list for the original master is no longer
updated. This means that there is a discrepancy between the list and the device.
Consequently, the GNRLLTMS warning status becomes TRUE as the saved primary
master is no longer considered connected. The list logic can be reset to clear the
clock list.
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When IEEE 1588 v2 time synchronization is used, the recommended
maximum num-ber of network hops from the grandmaster is 15 to
ensure that the total inaccuracy stays within 1 μs. The grandmaster
and each switch on the path must comply with the performance
requirements set by the selected profile.
The protection relay is an ordinary clock which can operate either in
slave-only and slave or master mode.
1MRS759142 F
IP SNTP secondary as "0.0.0.0".
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REX640