ABB Relion 670 series, Applications Manual

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Table 24: Definition of long lines
Line category Un Un
110 kV 500 kV
Long lines 77 km - 99 km 350 km - 450 km
Very long lines > 99 km > 450 km
As mentioned in the previous chapter, 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).
7.5.2.7 Parallel line application with mutual coupling
SEMOD154680-148 v1
General
SEMOD154680-150 v2
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 to 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 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:
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 class3 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 we can have 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 zone1 will be different depending on the operation
condition of the parallel line. It is therefore recommended to use the different setting groups
to handle 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.
Section 7 1MRK 505 343-UEN B
Impedance protection
248
Application manual