Figure 88 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 89. 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.
R
X
Distance measuring zone
Phase selection
”Quadrilateral” zone
IEC09000049-1-en.vsd
IEC09000049 V1 EN-US
Figure 89: Operating characteristic for FDPSPDIS (21) in forward direction for three-phase
fault, ohm/phase domain
The result from rotation of the load characteristic at a fault between two phases is presented in
fig
90. Since the load characteristic is based on the same measurement as the quadrilateral
characteristic, it will rotate with the quadrilateral characteristic clockwise by 30 degrees when
subject to a pure phase-to-phase fault. At the same time the characteristic will "shrink", divided by
2/√3, from the full
RLdFw
and
RLdRv
reach, which is valid at load or three-phase fault.
Section 7 1MRK 502 066-UUS B
Impedance protection
208
Technical manual
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