Transformer differential protection can experience false trips and mis-coordination, especially during external feeder faults and magnetizing inrush conditions. These malfunctions can compromise supply continuity, reduce system reliability, and put unnecessary stress on critical substation equipment. This research examines the reliability of the existing differential protection scheme at Corner Stone Substation and develops an enhanced adaptive configuration aimed at mitigating false operations while ensuring secure and selective fault clearance. To establish a performance baseline, historical relay event records from 2024 to 2025 were analyzed. A detailed MATLAB/Simulink model of the 15MVA, 33/11kV transformer protection system was created. The baseline protection scheme was tested under internal faults, external feeder faults, and transformer energization conditions. Subsequently, an improved protection configuration that integrates adaptive directional logic was implemented and validated through comparative simulations. The study found that the existing differential protection at Corner Stone Substation was reliable during internal faults, operating within 100 to 120 milliseconds. However, it was prone to false tripping during transformer energization, which produced an inrush current of approximately 6000 A with significant second harmonic distortion. Additionally, mis-coordination occurred during external feeder faults exceeding 7kA, with trip times ranging from 60 to 100 milliseconds. By integrating adaptive directional logic, the new scheme achieved secure restraint during external faults while maintaining rapid isolation of internal faults in less than 120 milliseconds. MATLAB simulations confirmed that the improved configuration enhanced selectivity, minimized false operations, and ensured reliable coordination between transformer and feeder protections. The findings indicate that adaptive directional differential protection improves selectivity, reduces false operations, and ensures robust coordination between transformer and feeder protections. This advancement contributes to enhancing protection strategies for modern substations and has potential applications for mitigating relay misoperations in other high-voltage grid systems.
Amadi et al. (Thu,) studied this question.