2 Functions
48
7ST6 Manual
E50417-G1176-C251-A3
2.2.2
Distance Protection with Combined Tripping Characteristic
With this tripping characteristic, the curves are constituted by one circle segment and
several straight lines.
The radius „Z“ of the circle segment defines the reach of the associated tripping zone.
The circle segment is limited by the directional straight lines „
β
“ and „
γ
“.
In addition, an area „
α
+ R“ can be cut from the circle segment in order to adapt the
tripping characteristic better to the load impedance.
This allows a better distinction between fault and load range, and an improved behav-
iour of the protection function is the presence of arc faults and close-up faults with
transformer saturation.
For each single curve, the direction characteristic can be selected independently;
options are „Forward“, „Forward extended“, „Reverse“ and „Non-directional“.
The setting „Forward extended“ has the same curve as the forward setting. In addition,
the curve for close-up faults is extended to non-directional. This extension takes place
if the secondary voltage has a value of less than 1 V, and the absolute value of the
measured impedance is within the tripping zone.
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