• Parallel line with common positive and zero sequence network
• Parallel circuits with common positive but isolated zero-sequence network
•
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 grounded 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
grounded 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-ground faults in the
following ways, by using:
• The possibility of different setting values that influence the ground-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. The application guide
mentioned below recommends in more detail the setting practice for this particular type
of line. The basic principles also apply to other multi circuit lines.
Parallel line applications
SEMOD168232-169 v2
This type of networks are defined as those networks where the parallel transmission
lines terminate at common nodes at both ends. We consider the three most common
operation modes:
• parallel line in service
• parallel line out of service and grounded
• parallel line out of service and not grounded
Parallel line in service
SEMOD168232-176 v3
This type of application is very common and applies to all normal sub-transmission
and transmission networks.
Here is the description of what happens when a fault occurs on the parallel line, as
shown in figure
72.
Section 8 1MRK 504 163-UUS A
Impedance protection
196 Transformer protection RET670 2.2 ANSI
Application manual
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