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1MRK 506 369-UEN B
8.9.2.6
Line distance protection REL670 2.2 IEC
Application manual
to achieve high sensitivity for phase-to-earth fault at remote line end of a long line
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 27, long lines have Source
impedance ratio (SIR's) less than 0.5.
Table 27:
Typical length of long and very long lines
Line category
Un
110 kV
Long lines
77 km - 99 km
Very long lines
> 99 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 149.
Parallel line application with mutual coupling
General
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.
From an application point of view there exists three types of network
configurations (classes) that must be considered when making the settings for the
protection function.
The different network configuration classes are:
1.
Parallel line with common positive and zero sequence network
2.
Parallel circuits with common positive but isolated zero sequence network
3.
Parallel circuits with positive and zero sequence sources isolated.
Impedance protection
Un
500 kV
350 km - 450 km
> 450 km
GUID-8136A6E6-085F-46A1-9BB4-F02730393D02 v1
Section 8
M17048-417 v2
297
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