Synchronization Alternatives - ABB RELION 630 Series Technical Manual

Section 3
Basic functions
3.16.8.2
104
directly for synchronization, that is, for adjusting the internal clock to obtain zero
offset at the next coming time message.
• If the synchronization message has an offset that is large compared to the other
messages, a spike-filter in the IED removes this time-message.
• If the synchronization message has an offset that is large, and the following
message also has a large offset, the spike filter does not act and the offset in the
synchronization message is compared to a threshold that defaults to 500
milliseconds. If the offset is more than the threshold, the IED is brought into a safe
state and the clock is set to the correct time. If the offset is lower than the
threshold, the clock is adjusted with 10 000 ppm until the offset is removed. With
an adjustment of 10 000 ppm, it takes 50 seconds to remove an offset of 500
milliseconds.
Synchronization messages configured as coarse are only used for initial setting of the
time. After this has been done, the messages are checked against the internal time and
only an offset of more than 10 seconds resets the time.
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 time-out is set so that one message can be lost without getting a TSYNCERR, but
if more than one message is lost, a TSYNCERR is given.

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.
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
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