16.1.3.2 Real-time clock (RTC) operation
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The IED has a built-in real-time clock (RTC) with a resolution of one second. The
clock has a built-in calendar that handles leap years through 2100.
Real-time clock at power off
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During power off, the system time in the IED is kept by a capacitor-backed real-
time clock that will provide 5 ppm accuracy for at least two days. This means that
if the 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
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Time synchronization startup procedure
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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.
Rate accuracy
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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
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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.
16.1.3.3 Synchronization alternatives
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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
Section 16 1MRK 505 384-UEN A
Basic IED functions
654 Breaker protection REQ650 2.2 IEC
Technical manual
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