Authors: Sanjay B. Amrutkar, Dr. Dolly Thankanchan
Abstract: Transformer energization is commonly accompanied by severe inrush currents that may lead to protection maloperation, thermal stress, and power quality degradation. This paper presents a comprehensive comparative investigation of transformer inrush current mitigation using voltage ramping and closed-loop flux linkage control strategies. A nonlinear transformer model incorporating magnetic saturation and core losses is developed to evaluate peak inrush current, inrush ratio, thermal stress expressed through the i^2 t index, and control effort under multiple energization conditions. Simulation results demonstrate that the uncompensated case exhibits a peak inrush current of 83.37 A, corresponding to an inrush ratio of 16.47 and significant thermal stress. Voltage ramping effectively limits the peak inrush current to 7.15 A, achieving an inrush ratio of 1.41 and reducing the i^2 t energy by approximately 97%. The flux control strategy, while requiring higher injected voltage and control energy, maintains inrush currents below 16.3 A under ideal conditions and demonstrates strong robustness against residual flux and unfavorable switching angles, with peak inrush currents of 14.69 A and 7.94 A, respectively. Total harmonic distortion values approach 100% for all cases due to the non-periodic and transient nature of inrush current, indicating that THD is not a reliable metric during transformer energization. The results highlight the trade-off between mitigation effectiveness and control effort, and confirm the superior robustness of flux-based control under practical energization uncertainties.
DOI: http://doi.org/10.5281/zenodo.20855803
