Parallel Line Application With Mutual Coupling - ABB REL670 2.2 IEC Applications Manual

Section 8
Impedance protection
8.1.2.6
152
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-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), as shown in figure 58.
ARGLd
ARGLd
RLdRv RLdFw
IEC05000220 V1 EN-US
Figure 58: Characteristic for zone measurement for long line with load
encroachment activated

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 to experience
mutual coupling, and some coupling exists even for lines that are separated by 100
meters or more. The reason to the introduced error in measuring due to mutual
coupling is the zero sequence voltage inversion that occurs.
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 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. Those are:
Zm
ZL
ARGLd
R
ARGLd
en05000220.vsd
1MRK 506 369-UEN B
SEMOD168232-149 v2
SEMOD168232-151 v2
Line distance protection REL670 2.2 IEC
Application manual