ABB Relion 670 series, Руководство по применению, Страница: 295 / 760

R
X
IEC08000437.vsd
IEC08000437 V1 EN-US
Figure 178: 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.
7.10.3 Load encroachment characteristics
GUID-DD9A62C3-A56D-411B-8303-6F7BC4C6092D v1
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 291 .
L
L
X1
arctan
R1
+
j =
+
XN
RN
EQUATION2115 V1 EN-US
(Equation 291)
But in some applications, for instance cable lines, the angle of the loop might be less than the
set angle. In these applications, the settings of fault resistance coverage in forward and
reverse direction, RFFwPE and RFRvPE for phase-to-earth faults and RFFwPP and RFRvPP for
phase-to-phase faults have to be increased to avoid that the phase selection characteristic
must cut off some part of the zone characteristic. The necessary increased setting of the fault
1MRK 505 343-UEN B Section 7
Impedance protection
289
Application manual