Function Description - Siemens SIPROTEC 5 Manual

3. Broken-wire blocking (Protection-function group)
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The Broken-wire blocking marker immediately leads to blocking of the protection functions that pick up
on unbalanced currents (for example, differential protection).
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Figure 8-14
8.3.5.3

Function Description

Broken Wire Suspected
The Broken-wire detection function monitors the dynamic behavior of the currents of each phase and of all
measuring points. For this purpose, the instantaneous values of the currents are checked for their plausibility.
Each expected violation must be confirmed by additional criteria before a wire break can be detected and
signaled with assurance.
NOTE
i
i
If the secondary circuits of the current transformers are accidentally opened while the broken-wire detec-
tion is on, functions like the differential protection are blocked phase-segregated and no longer initiate trip-
ping. Hazardous overvoltages can be generated at the open circuit of the current transformer in this condi-
tion which are not eliminated because the differential protection is blocked.
The detection of the local broken wire suspected is performed on each 3-phase current measuring point of the
device selectively for each phase. Depending on the protected object, the detection is based on permanent
(line differential protection) or frequency-adjusted instantaneous values (transformer differential protection).
Detection:
A wire break initially manifests itself as a sudden decrease of the current below the minimum threshold of
0.06 I/I A plausibility test on one period of past instantaneous values confirms this condition. If the criteria
rated.
for the local wire break are satisfied, the affected phase is marked with Broken wire suspected.
SIPROTEC 5, Fault Recorder, Manual
C53000-G5040-C018-5, Edition 11.2017
Stages of the Broken-Wire Detection Function Using the Differential Protection
Supervision Functions
8.3 Supervision of the Secondary System
381