ABB RES670 Technical Manual page 775

1MRK 511 408-UUS A
Phasor measurement unit RES670 2.2 ANSI
Technical manual
power is off, the time in the IED may drift with maximum 0.5 second per day for two
days, and after this the time will be lost.
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
startup procedure" and .
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 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.
Section 22
Basic IED functions
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