Restricted Earth Fault Protection in Low-Impedance Grounded Systems With Inverter-Based Resources

A restricted earth fault (REF) protection element provides sensitive detection of ground faults near the neutral a transformer or generator. The sensitivity gains from REF are especially more valuable when equipment is low-impedance grounded phase differential (87T) ineffective. However, faces several challenges in systems, which becoming prevalent inverter-based resource (IBR) plants. Dependability may be compromised if zero-sequence current at terminal capacitive for an internal fault. Security jeopardized external faults, such as phase-to-phase-to-ground evolving with (CT) saturation. Using field events IBR plants and simulations, this paper discusses design improvements to systems. CT selection criteria setting guidance reliable operation provided. Finally, coverage provided by compared 87T highlight its benefits