8.3.2.5 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 well known that it is difficult to
achieve high sensitivity for phase-to-earth fault at remote line end of long lines when
the line is heavy loaded.
What can be recognized as long lines with respect to the performance of distance
protection can generally be described as in table
26, long lines have Source impedance
ratio (SIR’s) less than 0.5.
Table 28: Definition of long and very long lines
Line category
Un Un
110 kV 500 kV
Long lines 77 km - 99 km 350 km - 450 km
Very long lines > 99 km > 450 km
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-earth 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), see figure 98.
en05000220.vsd
R
Zm
ARGLd
ARGLd
ARGLd
ARGLd
RLdFwRLdRv
ZL
IEC05000220 V1 EN
Figure 98: Characteristic for zone measurement for a long line
[6]
8.3.2.6 Parallel line application with mutual coupling
[6] RLdRv=RLdRvFactor*RLdFw.
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 219
Application manual
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