en05000220.vsd
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IEC05000220 V1 EN-US
Figure 111: Characteristic for zone measurement for a long line
8.3.2.6 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.
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.
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 217
Application manual
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