ABB REL670 2.2 IEC, Applications Manual

Page: 272 / 908

protection is to consider this with the settings that is, to have a security margin
between the distance zone and the minimum load impedance. This has the
drawback that it will reduce the sensitivity of the protection that is, the ability to
detect resistive faults.
The IED has a built in function which shapes the characteristic according to the
right figure 4. The load encroachment algorithm will increase the possibility to
detect high fault resistances, especially for phase-to-earth faults at remote end. For
example for a given setting of the load angle
ARGLd for the load encroachment
function, the resistive blinder for the zone measurement can be expanded according
to the right in figure
136 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. ZMMPDIS 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).
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 136: Load encroachment phenomena and shaped load encroachment
characteristic
8.5.2.5 Short line application
SEMOD154680-105 v2
In short line applications, the major concern is to get sufficient fault resistance
coverage. Load encroachment is not so common. The line length that can be
recognized as a short line is not a fixed length; it depends on system parameters
such as voltage and source impedance, see table
"Short line application" .
Section 8
1MRK 506 369-UEN B
Impedance protection
266 Line distance protection REL670 2.2 IEC
Application manual