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 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 grounded 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 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.
Parallel line applications
M17048-560 v4
This type of networks is 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 grounded.
3. Parallel line out of service and not grounded.
Parallel line in service
M17048-424 v5
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
125.
Section 8 1MRK 504 163-UUS A
Impedance protection
266 Transformer protection RET670 2.2 ANSI
Application manual
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