ABB REL670 2.2 IEC, Руководство по применению

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built in algorithm which compensates the overreach tendency of zone 1, at the
exporting end. No settings are required for this function.
8.9.2.3 Load encroachment
GUID-86D5DE98-621C-40E6-9EBB-F23363C1DB4F v2
In some cases the load impedance might enter the zone characteristic without any
fault on the protected line. The phenomenon is called load encroachment and it
might occur when an external fault is cleared and high emergency load is
transferred on the protected line. The effect of load encroachment is illustrated to
the left in figure
149 . The entrance of the load impedance inside the characteristic
is of course not allowed and the way to handle this with conventional distance
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 of figure
149 . The load encroachment algorithm will increase the
possibility to detect high fault resistances, especially for phase-to-earth faults at
remote line end. For example, for a given setting of the load angle
ArgLd for Phase
selection with load encroachment, quadrilateral characteristic function
(FRPSPDIS), the resistive blinder for the zone measurement can be expanded
according to the figure
149 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 preferably be
switched off. See section
"Load impedance limitation, without load encroachment
function" .
The settings of the parameters for load encroachment are done in , FRPSPDIS
function.
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 295
Application manual