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Non-Directional Intermittent Ground-Fault Protection
Overview of Functions
A typical characteristic of intermittent ground faults is that they often extinguish automatically and strike
again after some time. The fault duration can last between a few milliseconds and many seconds. Thus, such
faults are not detected at all or not selectively by the ordinary overcurrent protection. If pulse durations are
extremely short, not all protection devices in a short-circuit path can pick up. Thus, selective tripping is not
ensured.
Due to the time delay of the overcurrent protection function, such faults are too short to initiate switching off
the faulted cable. The short-circuit protection can clear such ground faults selectively only if the ground faults
have become permanent.
But such intermittent ground faults already bear the risk of damaging the equipment thermally. This is why
SIPROTEC 5 devices feature a protection function that is able to detect such intermittent ground faults and
accumulates their duration. If the sum reaches a configurable value within a certain time, the limit of the
thermal rating has been reached. If intermittent ground faults are distributed over a long period or if the
ground fault disappears and does not restrike after some time, the equipment under load is expected to cool
down. Tripping is not necessary in this case.
The Non-directional intermittent ground-fault protection function is used to protect against intermittent
ground faults which occur, for example, in cables due to poor insulation or water ingress in cable joints.
Structure of the Function
The Non-directional intermittent ground-fault protection function can be used in protection function
groups with current measurement. The function is preconfigured by the manufacturer with 1 stage, and a
maximum of 2 stages can be operated simultaneously. The non-preconfigured stages are shown in gray in the
following figure.
[DwIntGFP, 1, en_US]
Figure 6-110
Structure/Embedding of the Function
6.13
6.13.1
6.13.2
Protection and Automation Functions
6.13 Non-Directional Intermittent Ground-Fault Protection
SIPROTEC 5, Overcurrent Protection, Manual
543
C53000-G5040-C017-8, Edition 07.2017
Содержание 7SJ82
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