ABB RED650, Руководство по применению

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7.1.2.3 Load encroachment
GUID-6785BF05-2775-4422-8077-A663D01C6C07 v6
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
54 . A load impedance within the
characteristic would cause an unwanted trip. The traditional way of avoiding this
situation is to set the distance zone resistive reach with a security margin to the
minimum load impedance. The drawback with this approach is that the sensitivity
of the protection to detect resistive faults is reduced.
The IED has a built in feature which shapes the characteristic according to the
characteristic shown in figure
54 . 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
ArgLd , the
resistive blinder for the zone measurement can be set according to figure 54
affording higher fault resistance coverage without risk for 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. .
R
Z1
ArgLd
RLdFw
IEC09000248-3-en.vsdx
X
RLdRv
[1]
IEC09000248 V3 EN-US
Figure 54: Load encroachment phenomena and shaped load encroachment
characteristic
[1]
[1] RLdRv=RLdRvFactor*RLdFw
Section 7
1MRK 505 393-UEN B
Impedance protection
112 Line differential protection RED650 2.2 IEC
Application manual