ABB REL670 2.2 IEC, Руководство по применению

Страница: 274 / 908

General
SEMOD154680-150 v2
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 measurement due to the mutual coupling
between the parallel lines. The lines need not to be of the same voltage in order to
experience mutual coupling, and some coupling exists even for lines that are
separated by 100 meters or more. The reason to the introduced error in measuring
due to mutual coupling is the zero sequence voltage inversion that occurs.
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 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. Those are:
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 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.
Section 8
1MRK 506 369-UEN B
Impedance protection
268 Line distance protection REL670 2.2 IEC
Application manual