Nevertheless, always set
RLdFwd
,
RldRev
and
LdAngle
according to the expected
maximum load since these settings are used internally in the function as reference
points to improve the performance of the phase selection.
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-US
Figure 190:
Load encroachment phenomena and shaped load encroachment
characteristic
8.13.2.4
Short line application
GUID-7FA1B585-C979-4D51-A502-9C4070B99F0E v2
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.
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
Table 34:
Definition of short and very short line
Line category
Vn
Vn
110 kV
500 kV
Very short line
0.75 -3.5 miles
3-15 miles
Short line
4-7 miles
15-30 miles
The IED's ability 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
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
401
Application manual
Summary of Contents for RELION RET670
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