Short Line Application - ABB RELION RET670 Applications Manual

1MRK 504 163-UUS A
8.9.2.4
Transformer protection RET670 2.2 ANSI
Application manual
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
The settings of the parameters for load encroachment are done in (21), FRPSPDIS (21)
function.
X
Zm
Load impedance area in
ANSI05000495 V2 EN-US
Figure 153: Load encroachment phenomena and shaped load encroachment
characteristic defined in Phase selection and load encroachment
function (FRPSPDIS, 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
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 30.
Table 30: Typical length of short and very short line
Line category Vn
110 kV
Very short line 0.75 -3.5mile
Short line 4-7 miles
forward direction
LdAngle
R
LdAngle
Vn
500 kV
3-15 miles
15-30 miles
Section 8
Impedance protection
function".
Zm
ZL
LdAngle
LdAngle
RLdFwd
RldRev
ANSI05000495_2_en.vsd
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R
327