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2 Functions
Note
The redundancy of different communication connections (for ring topology) requires a
consequent separation of the devices connected to the communication network. For
example, different communication routes should not be conducted via the same mul-
tiplexer card, as there is no alternative which could be used if the multiplexer card
should fail.
Establishing the
When the devices of a differential protection system are linked to each other and
Protection Data
switched on, they communicate by themselves. The successful connection is indicat-
ed by an annunciation, e.g. with „Rel2 Login", when device 1 has contacted device
Communication
2. All devices of a differential protection system inform each device of the successful
protection data communication.
Additionally, the protection data interface is indicated via which a healthy link is estab-
lished.
These are helpful features during commissioning and are described, together with
further commissioning tools, in Section „Mounting and Commissioning". But even
during operation, the regular communication of the devices can be checked to each
other.
Monitoring of
The communication is permanently monitored by the devices.
Communication
Single faulty data telegrams are not a direct risk if they occur only occasionally. They
are recognized and counted in the device which detects the disturbance and can be
read out per unit of time as statistical information (Annunciation → Statistic).
You can define a limit for the permissible rate of faulty data telegrams. When, during
operation, this limit is exceeded, an alarm is given (e.g. „PI1 Error", No. 3258 if
protection data interface 1 is affected). You may use this alarm to block the differential
protection, either via binary output and input, or via logical combination by means of
the integrated user-definable logic (CFC).
If several faulty telegrams or no data telegrams at all are received, this is regarded as
an Error as soon as a time delay for data disturbance alarm (default setting 100 ms,
can be altered) is exceeded. A corresponding alarm is output („PI1 Data fault",
No. 3229 for interface 1). If the system offers no alternative way of communication (as
ring topologies would do), the differential protection will stop operating. All devices are
affected by the disturbance, since the formation of differential currents and restraint
currents is no longer possible at any of the ends. The distance protection as the
second main protection function assumes complete protection over all zones, provid-
ed that it is configured, and that time overcurrent protection is configured as well as
the emergency function. As soon as data transmission has returned to normal, the
devices switch automatically back to differential protection mode or differential and
distance protection mode, depending on how they are configured.
If the communication is interrupted for a permanent period (which is longer than a set-
table time period), this can be regarded as a transmission Failure of the communica-
tion. A corresponding alarm is output (e.g. „PI1 Datafailure", No. 3230 for inter-
face 1). Otherwise the same reactions apply as for the data disturbance.
Transmission time jumps that, for example, can occur in case of switchover in the com-
munication network are recognized (e.g. „PI1 jump", No. 3254 for interface 1) and
corrected by the devices. The differential protection system continues to operate
without loss of sensitivity. The transmission times are measured again and updated
78
7SD5 Manual
C53000-G1176-C169-1
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