Practical considerations when protecting mutually coupled lines

Mutual coupling between parallel lines continues to be problematic for protection engineers. Ground distance and directional overcurrent elements are susceptible to mutual coupling, whether it is due to the impact on the apparent impedance or due to incorrect directional decisions during specific system configurations. This paper first provides insights into how mutual coupling affects ground distance, ground overcurrent, and directional elements in different system configurations. Next, it offers practical advice for identifying situations where mutual coupling must be considered using a case study. Finally, the paper provides step-by-step guidance for setting ground distance and directional overcurrent elements on transmission lines that are affected by mutual coupling.