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 113.
en05000220_ansi.vsd
R
Zm
LdAngle
LdAngle
LdAngle
LdAngle
RLdFwdRLdRev
ZL
ANSI05000220 V1 EN
Figure 189: Characteristic for zone measurement for a long line
[2]
8.13.2.6 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 zero sequence measurement due to the mutual
coupling between the parallel lines. The lines need not be of the same voltage in order to
have mutual coupling, and some coupling exists even for lines that are separated by 100
meters or more. The mutual coupling 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.
[2] RLdRv=RLdRvFactor*RLdFw.
Section 8 1MRK 506 369-UUS -
Impedance protection
390 Line distance protection REL670 2.2 ANSI
Application manual
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