Parallel Line Application With Mutual Coupling - ABB RED650 Applications Manual

Section 7
Impedance protection
7.1.2.6
114

Parallel line application with mutual coupling

General
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 earthed 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 earthed at both ends.
The distance protection within the IED can compensate for the influence of a zero
sequence mutual coupling on the measurement at single phase-to-earth faults in the
following ways, by using:
• The possibility of different setting values that influence the earth-return
compensation for different distance zones within the same group of setting
parameters.
• Different groups of setting parameters for different operating conditions of a
protected multi circuit line.
1MRK 505 393-UEN B
GUID-4720AB55-0E59-4531-AE14-6A6EEC72C924 v1
GUID-E2FFF4A4-7D81-4440-87CE-3DCEAE2E42BD v2
Line differential protection RED650 2.2 IEC
Application manual