Siemens SIPROTEC 7SD610 Manual page 52

Functions
2.2 Protection Data Interfaces and Protection Data Topology
Monitoring the communication
The communication is permanently monitored by the devices.
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 informa-
tion (Annunciation → Statistic).
You can define a limit for the permissible rate of faulty data telegrams. When, during operation, this limit is ex-
ceeded, an alarm is given (e.g. „PI1 Error", No. 3258). You may use this alarm to block the differential pro-
tection, 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 a communication error
as soon as a time delay for data disturbance alarm of 100 ms (default setting, can be altered) is exceeded. A
corresponding alarm is output („PI1 Data fault", No 3229). The differential protection is then out of oper-
ation. Both devices are affected by the disturbance, since the formation of differential currents and restraint cur-
rents is no longer possible at any of the ends. If the backup overcurrent protection is configured, it will be the
only short-circuit protection still active. As soon as the data communication works fault-free again, the devices
will automatically switch back to differential protection operation.
If the communication is interrupted for a permanent period (which is longer than a settable time period), this is
regarded as a transmission failure . A corresponding alarm is output („PI1 Datafailure", No 3230). Oth-
erwise the same reactions apply as for the data disturbance.
Operating time jumps that, for example, can occur in case of switchings in the communication network can be
recognized (alarm „PI1 jump", No 3254) and corrected by the device. The differential protection system con-
tinues to operate without loss of sensitivity. The transmission times are measured again and updated within
less than 2 seconds. If GPS synchronization (with satellite receiver) is used, asymmetric transmission times
are recognized and corrected immediately.
The maximum permissible unbalance of the operating times can be set. This has a direct influence on the sen-
sitivity of the differential protection. The automatic self-restraint of the protection adapts the restraint quantities
to this tolerance so that a spurious pickup of the differential protection by these influences is excluded. Thus,
higher tolerance values reduce the sensitivity of the protection, which may be noticeable in case of very low-
current faults. With GPS-synchronization, transmission time differences do not affect the sensitivity of the pro-
tection as long as GPS-synchronization is intact. When the GPS–synchronization detects that the permissible
time difference is exceeded during operation, the message „PI 1 PD unsym." (No 3250) will be issued.
When a transmission time jump exceeds the maximum permissible transmission operating time, this is annun-
ciated. If transmission time jumps occur frequently, the regular operation of the differential protection is no
longer ensured. The differential protection can be blocked via a setting parameter (e.g. 4515 PI1 BLOCK
UNSYM) An alarm is output („PI1 unsym.", No 3256). This blocking can only be reset via a binary input
(„>SYNC PI1 RESET", No 3252).
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SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011