such that one message can be lost without getting a TSYNCERR, but if more than one
message is lost, a TSYNCERR is given.
20.6.3.3
Synchronization alternatives
Four main alternatives of external synchronization sources are available. The
synchronization message is applied:
•
via any of the communication ports of the IED as a telegram message including
date and time
•
as a minute pulse connected to a binary input
•
via GPS
•
via IRIG-B or PPS
Synchronization via SNTP
SNTP provides a ping-pong method of synchronization. A message is sent from an
IED to an SNTP server, and the SNTP server returns the message after filling in a
reception time and a transmission time. SNTP operates via the normal Ethernet
network that connects IEDs together in an IEC 61850 network. For SNTP to operate
properly, there must be an SNTP server present, preferably in the same station. The
SNTP synchronization provides an accuracy that gives +/- 1 ms accuracy for binary
inputs. The IED itself can be set as an SNTP-time server.
SNTP provides complete time-information and can be used as both fine and coarse
time synch source. However SNTP shall normally be used as fine synch only. The
only reason to use SNTP as coarse synch is in combination with PPS as fine source.
The combination SNTP as both fine and coarse source shall not be used.
SNTP server requirements
The SNTP server to be used is connected to the local network, that is not more than 4-5
switches or routers away from the IED. The SNTP server is dedicated for its task, or
at least equipped with a real-time operating system, that is not a PC with SNTP server
software. The SNTP server should be stable, that is, either synchronized from a stable
source like GPS, or local without synchronization. Using a local SNTP server without
synchronization as primary or secondary server in a redundant configuration is not
recommended.
Synchronization via Serial Communication Module (SLM)
On the serial buses (both LON and SPA) two types of synchronization messages are
sent.
•
Coarse message is sent every minute and comprises complete date and time, that
is, year, month, day, hours, minutes, seconds and milliseconds.
•
Fine message is sent every second and comprises only seconds and milliseconds.
The SLM module is located on the Numeric processing module (NUM).
Section 20
1MRK502052-UEN B
Basic IED functions
1112
Technical manual
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