Load Encroachment Characteristics - ABB REL670 2.2 IEC Applications Manual

Section 8
Impedance protection
8.10.3
318
IEC08000437 V1 EN-US
Figure 162: Rotation of load characteristic for a fault between two phases
This rotation may seem a bit awkward, but there is a gain in selectivity by using the
same measurement as for the quadrilateral characteristic since not all phase-to-
phase loops will be fully affected by a fault between two phases. It should also
provide better fault resistive coverage in quadrant 1. The relative loss of fault
resistive coverage in quadrant 4 should not be a problem even for applications on
series compensated lines.

Load encroachment characteristics

The phase selector must at least cover the overreaching zone 2 in order to achieve
correct phase selection for utilizing single-phase autoreclosing for faults on the
entire line. It is not necessary to cover all distance protection zones. A safety
margin of at least 10% is recommended. In order to get operation from distance
zones, the phase selection output STCNDZ or STCNDLE must be connected to
input STCND on distance zones.
For normal overhead lines, the angle for the loop impedance φ for phase-to-earth
fault defined according to equation 268.
X
IEC08000437.vsd
Line distance protection REL670 2.2 IEC
1MRK 506 369-UEN B
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Application manual