ABB RELION REX640 Technical Manual page 1328

Protection and control

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Supervision functions

Operation principle

The operation of protection communication supervision can be described by using

a module diagram. All the modules in the diagram are explained in the next sections.

Figure 755: 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 continuously measures and observes 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. These output signals are set to the

FALSE state until the first telegram is received over the communication link and

supervision is started. 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.

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

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