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Blocking of the measuring units
If a trip command for a 1-pole tripping of the differential protection is provided, the distance protection is started
with a 30 ms delay in the "single-pole dead time" mode. In this state, all phase-to-phase loop measuring units
which are connected to the switched-off phase are blocked. The 30 ms delay is necessary, because the circuit
breaker has usually not been opened yet shortly after the trip command . If the fault type has not been recog-
nized completely during the valid measuring cycle and the other loops are only picked up during the next cycle,
an immediate blocking would lead to incomplete types of fault.
Figure 2-49
Logic diagram for the blocking of the distance protection
Switching onto a fault
If the circuit breaker is manually closed onto a short circuit, the distance protection can issue an instantaneous
trip command. By setting parameters it may be determined which zone(s) is/are released following a manual
close (refer to Figure 2-50). The line energization information (input „SOTF") is derived from the state recogni-
tion (see Section 2.25.1, Detection of the Circuit Breaker Position).
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Functions
2.5 Distance Protection
131
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