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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).
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). The differential protection is then out of operation. Both devices are affected
by the disturbance, since the formation of differential currents and restraint currents is
no longer possible at any of the ends. If the backup overcurrent protection is config-
ured, it will be the only short-circuit protection still active. As soon as the data commu-
nication 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 set-
table time period), this is regarded as a transmission failure . A corresponding alarm
is output („PI1 Datafailure", No 3230). Otherwise the same reactions apply as
for the data disturbance.
Operating time jumps that, for example, can occur in case of switchings in the com-
munication network can be recognized (alarm „PI1 jump", No 3254) and corrected
by the device. The differential protection system continues 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 trans-
mission times are recognized and corrected immediately.
The maximum permissible unbalance of the operating times can be set. This has a
direct influence on the sensitivity of the differential protection. The automatic self-re-
straint of the protection adapts the restraint quantities to this tolerance so that a spu-
rious 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 differ-
ences do not affect the sensitivity of the protection 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 op-
erating time, this is annunciated. 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).
2.2.2
Operating Modes of the Differential Protection
2.2.2.1
Mode: Log Out Device
General
The „Log out device" mode (also: Log out device functionally) is used to log the device
out of the line protection system with the local circuit breaker being switched off.
The remaining device continues to operate in "differential protection mode", the
special feature, however, is that only the locally measured currents are included in the
logic as differential currents. The behaviour is now comparable to a time overcurrent
7SD610 Manual
C53000-G1176-C145-4
2.2 Protection Data Interfaces and Protection Data Topology
51
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