ABB RELION RET670, Applications Manual

Page: 381 / 1016

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-ground 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
176 .
8.12.2.6 Parallel line application with mutual coupling
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General
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Introduction of parallel lines in the network is increasing due to difficulties to get
necessary land to build 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 level 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 common 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.
One example of class 3 networks could be the mutual coupling between a 400 kV line
and rail road overhead lines. This type of mutual coupling is not so common although
it exists and is not treated any further in this manual.
For each type of network class, there are three different topologies; the parallel line can
be in service, out of service, out of service and grounded in both ends.
The reach of the distance protection zone 1 shall be different depending on the
operation condition of the parallel line. This can be handled by the use of different
setting groups for handling the cases when the parallel line is in operation and out of
service and grounded at both ends.
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 375
Application manual