Synchronization Alternatives - ABB Relion 650 Series Technical Manual

Section 15
Basic IED functions
15.1.3.3
620
Time synchronization startup procedure
The first message that contains the full time (as for instance LON and SNTP) gives
an accurate time to the IED. After the initial setting of the clock, one of the three
following conditions happens with each of the coming synchronization messages
configured as FineSynchSource:
• If the synchronization message, which is similar to the other messages, has an
offset compared to the internal time in the IED, the message is used directly
for synchronization, which means, for adjusting the internal clock to obtain
zero offset at the next coming time message.
• If the synchronization message has a large offset compared to the other
messages, a spike-filter in the IED removes this time-message.
• If the synchronization message has a large offset 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 clock jumps a whole
number of seconds so the remaining offset is less than 500ms. The remaining
offset is then slowly adjusted with 1000 ppm until the offset is removed. With
an adjustment of 1000ppm it takes 500 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
The rate accuracy is the accuracy of the internal clock while the external time
signal is lost. In the IED, the rate accuracy at cold start is 2 ppm but if the IED is
synchronized for a while, the rate accuracy is approximately 0.2 ppm if the
surrounding temperature is constant.
Time-out on synchronization sources
All synchronization interfaces have a time-out, and a configured interface must
receive time synchronization messages regularly in order not to give an error signal
(TSYNCERR) that is reported from the INTERRSIG function block. The time-out
is such that one message can be lost without getting a TSYNCERR, but if more
than one message is lost, a TSYNCERR is given.

Synchronization alternatives

Three 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 IRIG-B or PPS
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