ABB RET670 Applications Manual page 171

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1MRK504116-UUS C

Application manual

The IED has a built in function which shapes the characteristic according to the right

figure of figure 49. The load encroachment algorithm will increase the possibility to

detect high fault resistances, especially for phase-to-ground faults at remote line end.

For example, for a given setting of the load angle LdAngle for Phase selection with

load encroachment, quadrilateral characteristic function (FDPSPDIS, 21), the resistive

blinder for the zone measurement can be expanded according to the figure

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 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. So, for

short lines, the load encroachment function could preferably be switched off. See

"Load impedance limitation, without load encroachment

The settings of the parameters for load encroachment are done in FDPSPDIS (21)

Load impedance area in

ANSI05000495 V2 EN

Load encroachment phenomena and shaped load encroachment

characteristic defined in Phase selection with load encroachment

function FDPSPDIS (21)

Short line application

Transmission line lengths for protection application purposes are classified as short,

medium and long. The definition of short, medium and long lines is found in IEEE Std

C37.113-1999. ). The length classification is defined by the ratio of the source

impedance at the protected line's terminal to the protected line's impedance (SIR).

SIR's of about 4 or greater generally define a short line. Medium lines are those with

SIR's greater than 0.5 and less than 4

forward direction

IED application

ANSI05000495_2_en.vsd

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