Suitability analysis of practical directional algorithms for use in directional comparison bus protection based on IEC61850 process bus

A directional comparison bus protection can provide a high-speed bus fault clearing in an IEC61850 process-bus environment. This technique is based on fault direction for each circuit connected to the protected bus. Compared to biased current differential protection, the loss of accurate time synchronisation of the individual merging units does not cause the bus protection based on directional comparison to lose security. The suitability of various practical directional techniques is investigated from the viewpoint of directional comparison bus protection for an IEC61850 process bus. A modification in the superimposed directional algorithm for bus protection is proposed to overcome the major problems resulted from breaker operations. As a part of this modification, a new technique is proposed to determine the bus voltage from feeder voltages to avoid the need for an additional three-phase CVT on the bus. PSCAD/EMTDC and MATLAB are utilised to simulate the power system and various directional algorithms, respectively. Results are reported and compared.