8.1.2.5 Long transmission line application
For long transmission lines the margin to the load impedance that is, to avoid load
encroachment, will normally be a major concern. It is difficult to achieve high sensitivity
for line to ground-fault at remote end of a long lines when the line is heavy loaded.
Definition of long lines with respect to the performance of distance protection can
generally be described as in table
18, long lines have SIR’s less than 0.5.
Table 18: Definition of long lines
Line category
Vn Vn
110 kV 500 kV
Long lines 45-60 miles 200-250 miles
Very long lines >60 miles >250 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 at the same time as the security is improved (risk for unwanted
trip due to load encroachment is eliminated), as shown in figure
60.
en05000220_ansi.vsd
R
Zm
LdAngle
LdAngle
LdAngle
LdAngle
RLdFwdRLdRev
ZL
ANSI05000220 V1 EN
Figure 60: Characteristic for zone measurement for long line with load
encroachment activated
Section 8 1MRK 506 369-UUS -
Impedance protection
162 Line distance protection REL670 2.2 ANSI
Application manual
To Next Page
Loading...
