encroachment, quadrilateral characteristic function (FDPSPDIS, 21), the resistive blinder
for the zone measurement can be expanded according to the figure 112 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 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 section
"Load
impedance limitation, without load encroachment function".
The settings of the parameters for load encroachment are done in FDPSPDIS (21)
function.
R
X
Zm
RldRev
R
Zm
RLdFwd
ZL
ANSI05000495_2_en.vsd
Load impedance area in
forward direction
LdAngle
LdAngle
LdAngle
LdAngle
ANSI05000495 V2 EN
Figure 112: Load encroachment phenomena and shaped load encroachment
characteristic defined in Phase selection with load encroachment
function FDPSPDIS (21)
8.3.2.4 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
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 229
Application manual
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