Load Encroachment Characteristics - ABB RELION RET670 Applications Manual

1MRK 504 163-UUS A
8.10.3
Transformer protection RET670 2.2 ANSI
Application manual
IEC08000437 V1 EN-US
Figure 166: 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 PHSELZ or PHSELI must be connected to input PHSEL on distance
zones.
Impedance protection
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IEC08000437.vsd
Section 8
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