2 Functions
80
7SA522 Manual
C53000-G1176-C155-3
2.2.2 Distance protection with quadrilateral characteristic (optional)
The 7SA522 distance protection may optionally be provided with polygonal tripping
characteristic or with a MHO circle characteristic, or with both depending on which
version was ordered. If both characteristics are available, they may be selected sep-
arately for phase-phase loops and phase-earth loops. If only the MHO circle charac-
teristic is desired, please continue with the following Section.
2.2.2.1 Method of Operation
Operating Poly-
gons
In total there are five independent and one additional controlled zone for each fault im-
pedance loop. Figure 2-18 shows the shape of the polygons as example. The first
zone is shaded and forward directional. The third zone is reverse directional.
In general, the polygon is defined by means of a parallelogram which intersects the
axes with the values R and X as well as the tilt ϕ
Dist
. A load trapezoid with the setting
R
Load
and ϕ
Load
may be used to cut the area of the load impedance out of the polygon.
The axial coordinates can be set individually for each zone; ϕ
Dist
, R
Load
and ϕ
Load
are
common for all zones. The parallelogram is symmetrical with respect to the origin of
the R–X–coordinate system; the directional characteristic however limits the tripping
range to the desired quadrants (refer to “Determination of Direction” below).
The R-reach may be set separately for the phase–phase faults and the phase–earth
faults to achieve a larger fault resistance coverage for earth faults if this is desired.
For the first zone Z1 an additional settable tilt α exists, which may be used to prevent
overreach resulting from angle variance and/or two ended infeed to short-circuits with
fault resistance. For Z1B and the higher zones this tilt does not exist.
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