ABB REG670 Applications Manual page 201

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
One example of class 3 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, 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 shall 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
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 earthed.
3. 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.
Let us analyze what happens when a fault occurs on the parallel line see figure 84.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 41.
U
ph
Z =
Z − Z
0
I + 3 I ⋅
ph 0
3 ⋅ Z
1
IECEQUATION1275 V2 EN
U
ph
=
I + 3 I ⋅ K
1 ph 0 N
Section 8
Impedance protection
(Equation 41)
195