Short Line Application - ABB RELION RET670 Applications Manual

Section 8
Impedance protection
8.5.2.5
296
The settings of the parameters for load encroachment are done in the Phase selection
with load enchroachment, quadrilateral characteristic (FDPSPDIS,21).
X
Zm
Load impedance area in
ANSI05000495 V2 EN-US
Figure 140: 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
Table 28: Definition of short and very short line
Line category Vn
110 kV
Very short line 0.75-3.5 miles
Short line
4-7 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 140.
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.
forward direction
LdAngle
R
LdAngle
"Short line
Vn
500 kV
3-15 miles
15-30 miles
1MRK 504 163-UUS A
Zm
ZL
LdAngle
LdAngle
RLdFwd
RldRev
ANSI05000495_2_en.vsd
application".
Transformer protection RET670 2.2 ANSI
Application manual
R
SEMOD154680-105 v2