ABB 615 series Technical Manual page 869

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615 series ANSI
Technical Manual
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Figure 445: Functional module diagram
Communication supervision
The protection communication is supervised because the differential calculation is
dependent on the refreshing of new analog phasor samples from the remote terminal
within the protection telegram. The new protection telegram also updates the status of the
binary signals sent by the remote terminal. The calculation of the differential current is
based on comparing the remote and local terminal measured current samples. It is
therefore essential that the protection communication telegrams are supervised and the
result of the sample latency calculation can be used further in the differential current
calculation. When the communication is able to receive telegrams correctly from the
remote end via the communication media, the communication is assumed to be operating
correctly and the COMM output is kept active.
Communication interference detector
The communication interference detector is continuously measuring and observing the
sample latency of the protection telegrams. This value is also available as monitored data.
The function provides three output signals of which only the corresponding one is active
at a time depending on if the protection communication supervision is in OK, WARNING or
ALARM. The OK state indicates the correct operation of the protection. The WARNING
state indicates that the protection is internally blocked due to detected interference. The
WARNING state is switched to ALARM if the interference lasts for a longer period. The
protection communication supervision can sometimes be in the WAITING state. This state
indicates that the terminal is waiting for the communication to start or restart from the
remote end terminal.
Timer
Once activated with the WARNING signal, the timer has a constant time delay value of five
seconds. If the communication failure exists after the delay, the ALARM output is
activated.
Section 6
Supervision functions
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