ABB Relion 670 Series RES670, Technical Manual

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Real-time clock at startup
At IED startup, the internal time is free running. If the RTC is still alive since the last up
time, the time in the IED will be accurate (may drift 35 ppm), but if the RTC power has
been lost during power off (will happen after 5 days), the IED time will start at
01-01-2003. For more information, please refer to section
"Time synchronization startup
procedure" .
Time synchronization startup procedure
The first message that contains the full time (as for instance IRIG-B and GPS) 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 5 milliseconds. If the offset is
more than the threshold (5ms), 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 (< 5ms) the clock is
adjusted with 1000ppm until the offset is removed.
Rate accuracy
The Rate accuracy is the accuracy of the internal clock while the external time signal is lost
(e.g. GPS lost). 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. It can take up to one hour after a cold start of the IED to reach to
a stable rate due to the normal warming-up procedure of the IED.
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.
1MRK 511 365-UUS A
Section 20
Basic IED functions
Phasor measurement unit RES670 2.1 ANSI 721
Technical manual