TRIP
output is not activated. The activation of the output of the second harmonic
blocking signal
BLK2H
deactivates the
TRIP
output.
4.6.1.5
Application
A ground-fault protection using an overcurrent element does not adequately protect the
transformer winding in general and the 87LOZREF winding in particular.
The restricted ground-fault protection is mainly used as a unit protection for the
transformer windings. 80LOZREF is a sensitive protection applied to protect the
87LOZREF winding of a transformer. This protection system remains stable for all the
faults outside the protected zone.
87LOZREF provides a higher sensitivity for the detection of ground faults than the overall
transformer differential protection. This is a high-speed unit protection scheme applied to
the 87LOZREF winding of the transformer. In 87LOZREF, the difference of the
fundamental component of all three phase currents and the neutral current is provided to
the differential element to detect the ground fault in the transformer winding based on the
numerical stabilized differential current principle.
Connection of current transformers
The connections of the main CTs are designated as "Type 1" and "Type 2". In case the
groundings of the current transformers on the phase side and the neutral side are both
either inside or outside the area to be protected, the setting parameter
CT connection type
is "Type 1".
If the grounding of the current transformers on the phase side is inside the area to be
protected and the neutral side is outside the area to be protected or vice versa, the setting
parameter
CT connection type
is "Type 2".
Section 4
1MRS240050-IB C
Protection functions
306
REF615R
Technical Manual
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