Time Domain Based Security Enhancement Methodologies for Transformer Differential Protection Scheme

This paper proposes security enhancement algorithms for transformer differential protection, which claims to augment the unit security by providing required sensitivity during internal fault conditions and stability for external faults. The proposed algorithm is executed by modelling a biased differential characteristic and developing algorithms for security issues in a transformer considering the most predominant system conditions i.e. inrush condition during transformer energization and CT saturation during heavy through fault conditions. Detection of inrush currents were performed using statistical analysis of differential power and using a discrimination index. CT saturation detection is independent of current waveform analysis and is based on the calculation of the saturation time. The proposed algorithms are evaluated and validated under different scenarios using MATLAB/Simulink environment and investigative study is performed. The results are visualized as current trajectories plotted on the relay operating characteristics summarized for easy conception of the algorithm.