Correct line parameters are crucial for reliable and selective operation of your distance protection device. It also allows an accurate fault location after an event on the line by evaluating the fault recorder. The set of parameters contains the positive sequence impedance, the zero sequence impedance and the k-factor. For double or multi-circuit lines the mutual coupling impedance is required in addition.
These parameters are often derived from network calculations, which do not represent the actual values due to unknown soil properties, such as different soil resistivities, water pipes or other buried conductors. This leads to a malfunction of your distance protection relay by under- and overreach. This results in outage and loss of grid stability.
Mutual CouplingShow more
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.
Line Impedance MeasurementShow more
Line Impedance Measurement
Distance protection as well as impedance-based fault location on overhead lines is widely used at utilities. Significant characteristics of the protected line are the positive-sequence impedance Z1 and the zero-sequence impedance Z0 which must be precisely known to make the relay reliably decide whether to trip or not to trip.