ABB RELION RET670, Applications Manual

Page: 269 / 1016

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-US
Figure 123: 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
M17048-97 v4
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
26 .
Table 26: Definition of short and very short line
Line category Vn Vn
110 kV 500 kV
Very short line 0.75 -3.5mile 3-15 miles
Short line 4-7 miles 15-30 miles
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 263
Application manual