Evaluation of relaying impedance algorithms for series-compensated line

• Fault-loop impedance measurement for a series-compensated line is investigated.
• Combination of differential equation method with orthogonalisation is recommended.
• Fault direction detection with incremental positive sequence signals is presented.

A group of the algorithms of fault-loop impedance determination for digital distance relay applied for protecting a series-compensated line has been considered. The algorithms gathered in two basic families have been tested: (i) the methods based upon Fourier orthogonal components with using both full-cycle and half-cycle data windows; (ii) four variants of the method founded on differential equation techniques, i.e. with applied various digital differentiation rules, with included additional pre-filtration and combined with orthogonal components determination. Extensive simulation studies have been performed for comparing the calculation techniques. Recommendations with respect to impedance algorithms suitable for protection of a series-compensated line have been stated. The other studied algorithm is related to fault direction discrimination for the considered series-compensated line arrangement. Sample simulation results have been presented and discussed.