ABB REL670 2.2 IEC, Applications Manual

Page: 304 / 908

One example of class 3 networks could be the mutual coupling between a 400kV
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 will 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.
Most multi circuit lines have two parallel operating circuits.
Parallel line applications
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This type of networks are defined as those networks where the parallel
transmission lines terminate at common nodes at both ends.
The three most common operation modes are:
1. parallel line in service.
2. parallel line out of service and earthed.
3. parallel line out of service and not earthed.
Parallel line in service
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This type of application is very common and applies to all normal sub-transmission
and transmission networks.
Let us analyze what happens when a fault occurs on the parallel line see figure 150 .
From symmetrical components, we can derive the impedance Z at the relay point
for normal lines without mutual coupling according to equation
236 .
Section 8
1MRK 506 369-UEN B
Impedance protection
298 Line distance protection REL670 2.2 IEC
Application manual