Fast and Reliable Method for Identifying Fault Type and Faulted Phases Using Band Limited Transient Currents

A method for fault type discrimination and faulted phase identification using instantaneous local current measurements is proposed. Seven current components are obtained from the measured three-phase instantaneous currents through a transformation and band passed filtered to remove the fundamental components and high frequency content. Upon detecting a fault, nine fault discrimination indices are computed taking different ratios of the maximum rates of change of these filtered current components. The indices are used to (i) separate ground faults from the phase-to-phase and three-phase faults, (ii) discriminate phase-to-ground from phase-to-phase-to-ground faults, (iii) differentiate phase-to-phase faults from the three-phase faults, and (iv) identify the faulted phases. As the indices are ratios, decisions are less affected by the fault resistance. The algorithm was validated using a power system simulated in PSCAD/EMTDC. Extensive testing involving more than 10,000 fault scenarios showed that fault type and faulted phases can be successfully identified. The algorithm found some difficulty in identifying the phases involved in phase-to-phase-to-ground faults at certain fault inception angles, and one of the thresholds can be affected by the transposition scheme.