Load Encroachment - ABB RELION 650 Series Applications Manual

1MRK 505 363-UEN A
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IEC09000247 V1 EN-US
Figure 55: Influence of fault current infeed from remote line end
The effect of fault current infeed from the remote line end is one of the most driving factors to
justify complementary protection for distance protection.
When the line is heavily loaded, the distance protection at the exporting end will have a
tendency to overreach. To handle this phenomenon, the IED has an adaptive built-in algorithm,
which compensates the overreach tendency of zone 1 at the exporting end. No settings are
required for this feature.
7.1.2.3

Load encroachment

In some cases the measured load impedance might enter the set zone characteristic without
any fault on the protected line. This phenomenon is called load encroachment and it might
occur when an external fault is cleared and high emergency load is transferred onto the
protected line. The effect of load encroachment is illustrated on the left in figure 56. The
entrance of the load impedance inside the characteristic is of course not desirable and the way
to handle this with conventional distance protection is to consider this with the resistive reach
settings, that is, to have a security margin between the distance zone characteristic and the
minimum load impedance. Such a solution has the drawback that it will reduce the sensitivity
of the distance protection, that is, the ability to detect resistive faults.
The IED has a built in feature which shapes the characteristic according to the characteristic
shown in figure 56. The load encroachment algorithm will increase the possibility to detect
high fault resistances, especially for phase-to-earth faults at the remote line end. For example,
for a given setting of the load angle
be set according to figure
unwanted operation due to load encroachment. Separate resistive blinder settings are
available in forward and reverse direction.
The use of the load encroachment feature is essential for long heavily 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. Load
encroachment is not a major problem. See section "".
Application manual
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IEC09000247-1-en.vsd
GUID-6785BF05-2775-4422-8077-A663D01C6C07 v5
Section 7
105