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Configuring the 56/64 kbit data
communication modules
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1. Transmit errors are due to that the terminal cannot send messages via the telecom-
munication channel (PCM). The line differential function initiates the sending of
one message every 5 ms. If this command can not be executed for 10 consecutive
times (= 10 x 5 ms) due to blocked, missing or unsynchronized communication
channel, COMFAIL is triggered. For non-consecutive interruptions, an integration
algorithm is used that prolongs the COMFAIL triggering time.
2. Receive errors occur when no expected messages are received. The line differential
function expects to receive one message every 5 ms. If this does not occur 10 con-
secutive times (= 10x5 ms), COMFAIL is triggered. For non-consecutive interrup-
tions, an integration algorithm is used that prolongs the COMFAIL triggering time.
3. Block differential protection. Block of differential protection occurs during change
of settings or setting group.
4. Remote terminal COMFAIL. For error No 1, 2, 3 and No 5, 6, 7, 8, 9, 10 the COM-
FAIL is sent in the second consecutive message (within 10 ms). Thus, some short
interruptions can be recorded only in one terminal. The communication channel
must be in operation to be able to receive this signal.
5. Time synchronization error refers to synchronization check and is only performed
by the terminal set as Slave for the internal differential clocks synchronization. If
50 time synchronization messages (included with every 8 line differential function
message) are not correctly received (= 8 x 5 ms x 50 = 2000 ms), COMFAIL will
be triggered. If more than 750 synchronization messages are not correctly received,
a re-synchronization of the internal differential clock will be made. For non-consec-
utive interruptions, an integration algorithm prolongs the COMFAIL triggering
time.
6. Differential Clock drift refers to a difference > 50 ms between the internal differen-
tial clocks in the differential protection in the terminal set as Slave and the one set
as Master for synchronization of the internal differential clock. The COMFAIL trig-
gering time depends on a number of factors from a drift compensation algorithm.
This check is normally not activated unless the communication channel has been
lost for a long time.
7. Communication channel loop delay-instantaneous is checked every 40 ms (at each
synchronization message). If the communication channel loop (Slave-Master-
Slave) delay is more than 31ms for one message, COMFAIL is triggered instanta-
neously. This check is done in the terminal set as Slave for the internal differential
clock by a comparison with the real time clock in the terminal at sending and receiv-
ing of a looped message.
8. Communication channel loop delay-time delayed checks if the communication
channel delay for transmitted and received signal is >24 ms (Local-Remote-Local).
The check is performed every 40 ms (at each synchronization message) by compar-
ing the real time clock time at sending and receiving of a looped message. COM-
FAIL is triggered after 50 consecutive messages with excessive loop time.
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