Selective and reliable distance protection of your double circuit line only works if the coupling impedance of the zero sequence system between two lines is taken into account. Especially for double circuit overhead lines, there is significant inductive and resistive coupling between the two systems.
Distance protection relays, which are capable of compensating the mutual coupling, are measuring the current of the parallel line. As a result of this the voltage caused by coupling can be corrected in order to avoid over- and underreach.
The determination of your double circuit lines parameters is quite similar to the single circuit line procedure. You only have to measure one additional loop which represents the coupling between the two systems. Based on these loop impedances, our test system finally calculates your required double circuit line parameters.