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Fault tracing
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
COMFAIL 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 per-
formed by the terminal set as Slave for the internal differential clocks synchroni-
zation. 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-consecutive interruptions, an integration algorithm prolongs
the COMFAIL triggering time.
6. Differential Clock drift refers to a difference > 50 ms between the internal differ-
ential 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 COM-
FAIL triggering time depends on a number of factors from a drift compensation
algorithm. This check is normally not activated unless the communication chan-
nel 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-Mas-
ter-Slave) delay is more than 31ms for one message, COMFAIL is triggered in-
stantaneously. 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 send-
ing and receiving 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-Lo-
cal). The check is performed every 40 ms (at each synchronization message) by
comparing the real time clock time at sending and receiving of a looped message.
COMFAIL is triggered after 50 consecutive messages with excessive loop time.
COMFAIL triggering time = 2000 ms (= 50x40 ms). For non-consecutive mes-
sages with excessive loop time, an integration algorithm is used that prolongs the
COMFAIL triggering.
9. Abnormal clock deviation checks if the synchronization in the Slave of the inter-
nal differential clocks in the differential protection have an abnormal deviation,
(Slave-Master–Slave). COMFAIL is triggered instantaneously, but will probably
only occur after long interruptions in the communication channel. However, the
start or re synchronization procedure can also activate COMFAIL due to this
function.
10. Data flow checks if the time between initiations of the sending messages from the
line differential function is longer than 20 ms, using the real time clock for the
check. This check will also trigger the COMFAIL if the external time synchroni-
zation of the real time clock by minute pulse or SPA/LON from Station Clock or
GPS, adjusts the terminal clock forward > 15 ms. The COMFAIL triggering is
instantaneous. The channel interruption measurements for short, medium and
long interruptions, presented on the HMI are based on measurements of timing
from the real time clock which are made independently in each terminal. These
measurements are also independent from the internal differential clock. The mea-
Chapter 8
Configuring the 56/64 kbit data
communication modules
61
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