controller 3BSE021180R1

controller 3BSE021180R1

controller 3BSE021180R1

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 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 mutual coupling does influence the zero sequence impedance to the fault point but it 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 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 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.