ABB REG670 Applications Manual page 226

Section 8
Impedance protection
220
General
Introduction of parallel lines in the network is increasing due to difficulties to get
necessary area for new lines.
Parallel lines introduce an error in the zero sequence measurement due to the mutual
coupling between the parallel lines. The lines need not be of the same voltage in order
to have mutual coupling, and some coupling exists even for lines that are separated by
100 meters or more. The mutual coupling does not normally cause voltage inversion.
It can be shown from analytical calculations of line impedances that the mutual
impedances for positive and negative sequence are very small (< 1-2%) of the self
impedance and it is a practice to neglect them.
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.
The different network configuration classes are:
1. Parallel line with common positive and zero sequence network
2. Parallel circuits with common positive but separated zero sequence network
3. Parallel circuits with positive and zero sequence sources separated.
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 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
This type of networks is defined as those networks where the parallel transmission
lines terminate at common nodes at both ends.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
Application manual