What can be recognized as long lines with respect to the performance of distance protection
can generally be described as in table
, long lines have Source impedance ratio (SIR’s) less
than 0.5.
Table 19: 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
.
en05000220.vsd
R
Zm
ARGLd
ARGLd
ARGLd
ARGLd
RLdFw
RLdRv
ZL
IEC05000220 V1 EN-US
Figure 126: Characteristic for zone measurement for a long line
7.3.2.6
Parallel line application with mutual coupling
M17048-417 v2
General
M17048-567 v3
Introduction of parallel lines in the network is increasing due to difficulties to get necessary
area for new lines.
Parallel lines introduce an error in the measurement due to the mutual coupling between the
parallel lines. The lines need not be of the same voltage in order to experience mutual coupling,
and some coupling exists even for lines that are separated by 100 meters or more. The mutual
coupling does influence the zero sequence impedance to the fault point but it does not
normally cause voltage inversion.
It can be shown from analytical calculations of line impedances that the mutual impedances
for positive and negative sequence are very small (< 1-2%) of the self impedance and it is a
practice to neglect them.
1MRK 505 343-UEN B
Section 7
Impedance protection
203
Application manual
Содержание Relion 670 series
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