ABB RELION 650 SERIES, Technical Manual

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• The maximum error of the last used synchronization message
• The time since the last used synchronization message
• The rate accuracy of the internal clock in the function.
19.1.3.2 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.
• 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
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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.
Section 19
1MRK 506 382-UEN A
Basic IED functions
804 Line distance protection REL650 2.2 IEC
Technical manual