ABB Relion 670 Series Technical Reference Manual page 234

Section 6
Impedance protection
228
IEC05000673 V1 EN
Figure 107: Operating characteristic in forward direction when load encroachment
is activated
Figure 107 is valid for phase-to-ground. During a three-phase fault, or load, when the
quadrilateral phase-to-phase characteristic is subject to enlargement and rotation the
operate area is transformed according to figure 108. Notice in particular what happens
with the resistive blinders of the "phase selection" "quadrilateral" zone. Due to the 30-
degree rotation, the angle of the blinder in quadrant one is now 90 degrees instead of
the original 60 degrees. The blinder that is nominally located to quadrant four will at
the same time tilt outwards and increase the resistive reach around the R-axis.
Consequently, it will be more or less necessary to use the load encroachment
characteristic in order to secure a margin to the load impedance.
X
"Phase selection"
"quadrilateral" zone
Distance measuring zone
Load encroachment
characteristic
R
Directional line
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en05000673.vsd
Technical reference manual