Evaluation of uncertainties in double line distance relaying. A global sight

Uncertainty sources, when relaying double lines with distance relays, during simple or intercircuit faults, are evaluated. Tendencies on errors and their magnitude are easily viewed in a forward reach settings vs. real fault distance covered plane. Contributions of different factors are separated and relations among them are established using the mentioned plane. Desired situations to be evaluated include any type of fault, for any previous state and any fault resistance, as well as any type of distance unit. The intent of the analytsis presented is not only to evaluate known tendencies of distancie relay responses, in double or single lines, but also to identify the causes and to show the usefulness of the employed methodology for any other type of study to be performed when calculating settings, analysing or designing the best protection philosophy in double or single lines.