ABB RELION RET670 Applications Manual page 355

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
IEC05000673 V1 EN-US
Figure 164: Operation characteristic in forward direction when load encroachment
is enabled
Figure 164 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 165. 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 100 degrees instead of
the original 70 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
Section 8
Impedance protection
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