A Streamlined Fault Detection and Selectivity Method Based on a Normalized Current Difference Criterion and Apparent Impedance for Onshore Wind Farm Collector Grids

The large-scale integration of inverter-based resources (IBRs) has substantially altered the magnitude, phase-angle behavior, and transient evolution of fault currents in modern power systems. These changes pose significant challenges to conventional protection schemes in wind farm collector grids. In such systems, the limited short-circuit current contribution from converter-interfaced wind turbines, together with variations in apparent impedance, can compromise relay performance. In this context, this paper proposes a streamlined two-stage feeder protection approach for onshore wind farm collector grids. In the first stage, faults are detected using a normalized current-difference criterion computed from pre-fault and fault current samples. In the second stage, internal and external faults are discriminated using the apparent positive-sequence fault impedance evaluated in the R-X plane. The method was assessed through 24,120 PSCAD-simulated fault scenarios based on a realistic wind farm model. All simulated fault cases were successfully detected, and all analyzed cases were correctly classified as internal or external under the studied conditions.Additional validation using nine real fault records confirmed the practical feasibility of the proposed approach and showed faster fault detection than the installed feeder relays in the analyzed events. Overall, the results indicate that the method enables fast, reliable protection decisions in wind-farm collector grids while maintaining low computational complexity.