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.