ABB Relion 670 series, Техническое руководство

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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.
21.1.3.2 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 2038.
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 35 ppm accuracy for 5 days. This means that if the power is off, the time in the IED may
drift with 3 seconds per day, during 5 days, and after this time the time will be lost completely.
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, SNTP 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 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 (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
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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.
1MRK 502 066-UUS B Section 21
Basic IED functions
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Technical manual