ABB REL670 2.2 IEC, Applications Manual

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resistive blinder for the zone measurement can be expanded according to the right
in figure
57 given higher fault resistance coverage without risk for unwanted
operation due to load encroachment. This is valid in both directions.
The use of the load encroachment feature is essential for long heavy loaded lines,
where there might be a conflict between the necessary emergency load transfer and
necessary sensitivity of the distance protection. The function can also preferably be
used on heavy loaded medium long lines. For short lines the major concern is to get
sufficient fault resistance coverage and load encroachment is not a major problem.
So, for short lines, the load encroachment function could preferable be switched
off.
The settings of the parameters for load encroachment are done in the Phase
selection with load enchroachment, quadrilateral characteristic (FDPSPDIS)
function.
R
X
Zm
Load impedance
area in forward
direction
RLdRv
R
Zm
ARGLd
ARGLd
ARGLd
ARGLd
RLdFw
ZL
en05000495.vsd
IEC05000495 V1 EN-US
Figure 57: Load encroachment phenomena and shaped load encroachment
characteristic
8.1.2.5 Long transmission line application
SEMOD168232-128 v3
For long transmission lines the margin to the load impedance that is, to avoid load
encroachment, will normally be a major concern. It is difficult to achieve high
sensitivity for line to earth-fault at remote end of a long lines when the line is
heavy loaded.
Definition of long lines with respect to the performance of distance protection can
generally be described as in table
18 , long lines have SIR’s less than 0.5.
Table 18: Definition of long lines
Line category Un Un
110 kV 500 kV
Long lines 77 km - 99 km 350 km - 450 km
Very long lines > 99 km > 450 km
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 151
Application manual