ABB RELION 670 Series Applications Manual page 156

Section 7
Impedance protection
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:
• 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 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.
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
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 earthed
• parallel line out of service and not earthed
Parallel line in service
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 59.
From symmetrical components, it is possible to derive the impedance Z at the IED point for
normal lines without mutual coupling according to equation 42.
Z =
I
EQUATION1275 V3 EN-US
150
V
ph
=
-
Z Z I
0 1
+ ×
3I
ph 0
×
3 Z
1
V
ph
I
+ ×
3 K
ph N
0
1MRK 504 152-UEN B
SEMOD168232-169 v2
SEMOD168232-176 v3
(Equation 42)
Application manual