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 129: Load encroachment phenomena and shaped load encroachment
characteristic
Short line application
In short line applications, the major concern is to get sufficient fault resistance
coverage. Load encroachment is not so common. The line length that can be
recognized as a short line is not a fixed length; it depends on system parameters such as
voltage and source impedance, see table "Short line application".
Table 62: Definition of short and very short line
Line category
Vn Vn
110 kV 500 kV
Very short line
Short line
0.75-3.5 miles 3-15 miles
4-7 miles 15-30 miles
The possibility in IED to set resistive and reactive reach independent for positive and
zero sequence fault loops and individual fault resistance settings for phase-to-phase
and phase-to-ground fault together with load encroachment algorithm improves the
possibility to detect high resistive faults without conflict with the load impedance, see
figure
129.
For very short line applications the underreaching zone 1 can not be used due to that
the voltage drop distribution through out the line will be too low causing risk for
overreaching.
Load encroachment is normally no problems for short line applications so the load
encroachment function could be switched off (OperationLdCmp = Off). This will
increase the possibility to detect resistive close-in faults.
1MRK504116-UUS C Section 3
IED application
289
Application manual
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