Synchronization Alternatives - ABB RET650 Technical Manual

Section 17
Basic IED functions
17.2.8.3
570

Synchronization alternatives

Two main alternatives of external time synchronization are available. The
synchronization message is applied either via any of the communication ports of the
IED as a telegram message including date and time or via IRIG-B.
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 shall SNTP 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 IRIG-B
IRIG-B is a protocol used only for time synchronization. A clock can provide local
time of the year in this format. The "B" in IRIG-B states that 100 bits per second are
transmitted, and the message is sent every second. After IRIG-B there numbers stating
if and how the signal is modulated and the information transmitted.
To receive IRIG-B there are one dedicated connector for the IRIG-B port. IRIG-B 00x
messages can be supplied via the galvanic interface, where x (in 00x) means a number
in the range of 1-7.
If the x in 00x is 4, 5, 6 or 7, the time message from IRIG-B contains information of
the year. If x is 0, 1, 2 or 3, the information contains only the time within the year, and
year information has to come from the tool or local HMI.
The IRIG-B input also takes care of IEEE1344 messages that are sent by IRIG-B
clocks, as IRIG-B previously did not have any year information. IEEE1344 is
compatible with IRIG-B and contains year information and information of the time-
zone.
It is recommended to use IEEE 1344 for supplying time information to the IRIG-B
module. In this case, send also the local time in the messages.
1MRK 504 135-UEN A
Technical manual