The following mechanisms are applied:
•
For reporting the direction result, the fundamental-component value of the zero-sequence voltage must
exceed the V0> threshold value in a time slot of 100 ms after the ground-fault ignition. This effec-
tively suppresses wrong indications as a result of switching operations.
•
The fundamental-component value of the zero-sequence voltage V0 is not influenced by switching oper-
ations and is thus a good criterion for distinguishing the ground fault from a switching procedure. The
condition that the fundamental-component value must exceed the V0> threshold value for
reporting the direction result effectively suppresses the influence of switching operations.
For rare cases in which high zero-sequence voltages occur over longer time ranges after switching off the
feeder or line, a criterion based on the positive-sequence current is also effective. This criterion compares
the positive-sequence current before and after the transient event and thus detects a disconnection. In
case of disconnection, the direction result is not reported.
Through stabilization mechanisms, the direction result is reported 100 ms after the ground-fault ignition.
Thus a pickup occurs with a 100-ms delay.
If the stage is used in a 1-phase function group, the additional criterion via the positive-sequence current
is not effective.
•
The function detects transient occurrences in the zero-sequence voltage. In systems with operational
zero-sequence voltages, if the measuring voltage is switched on, the function can internally be started. If
the fundamental-component value of the zero-sequence voltage does not exceed the threshold of the
Maximum operational V0 parameter in a time slot of 100 ms after the function start, the function is
reset internally.
Trip Logic
[loauswis-240113-01.tif, 3, en_US]
Figure 6-132
Trip Logic Diagram
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 581
C53000-G5040-C017-8, Edition 07.2017
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