Functions
2.14 Monitoring Functions
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
167
Wire Break Monitoring
During steady-state operation the broken wire monitoring detects interruptions in the secondary circuit of the
current transformers. In addition to the hazardous potential caused by high voltages in the secondary circuit,
this kind of interruptions simulate differential currents to the differential protection, such as those evoked by
faults in the protected object.
The broken wire monitoring function monitors the local phase currents of all three phases and the results of the
broken wire monitoring supplied by the device at the other end of the protected object. At each sampling
moment, the function checks whether there is a jump in one of the three phase currents; if there is, it generates
the „suspected wire break“ signal.
There is a suspected local wire break if a jump has been detected in the affected phase and the current has
dropped to 0 A.
WARNING!
If the CT secondary circuits are inadvertently opened while the broken wire monitoring is activated, the differ-
ential protection is blocked phase-selectively and does not trip anymore!
This state may give rise to hazardous overvoltages in the open CT circuit, which will not lead to a trip because
the differential protection is blocked.
Figure 2-67
Generation of the local wire break
