Application - ABB RELION REX640 Technical Manual

Section 6
Supervision functions
6.4.5
1224
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.

Application

Communication principle
Analog samples, trip-, start- and user programmable signals are transferred in each
protection telegram and the exchange of these protection telegrams is done eight times
per power system cycle (every 2.5 ms when F
Master-Master communication arrangement is used in the two-terminal line
differential solution. Current samples are sent from both line ends and the protection
algorithms are also executed on both line ends. The direct-intertrip, however, ensures
that both ends are always operated simultaneously.
Time synchronization
In numerical line differential protection, the current samples from the protections
which are located geographically apart from each other must be time coordinated so
that the current samples from both ends of the protected line can be compared without
introducing irrelevant errors. The time coordination requires an extremely high
accuracy.
As an example, an inaccuracy of 0.1 ms in a 50 Hz system gives a maximum amplitude
error of approximately around 3 percent. An inaccuracy of 1 ms gives a maximum
amplitude error of approximately 31 percent. The corresponding figures for a 60 Hz
system are 4 and 38 percent respectively.
In the protection relay, the time coordination is done with an echo method. The
protection relays create their own time reference between each other so that the system
clocks do not need to synchronize.
= 50 Hz).
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1MRS759142 C
REX640
Technical Manual