Controlled pre-magnetization method for inrush current reduction in electric arc furnace transformers

Abstract

This paper investigates transformer inrush currents during the energisation of arc furnace transformers in electric arc furnace (EAF) power supply systems. The study focuses on an industrial DSP-100 installation operating with harmonic filters and reactive-power compensation equipment. A nonlinear reduced-order lumped-parameter model is formulated using explicit phase-domain relations for the supplying-system equivalent, the furnace-transformer branch, the connected filter/compensation branches, and the nonlinear magnetic circuit. The surviving DSP-100 oscillograms are used as an experimental anchor and for a waveform-level consistency assessment of peak current, inter-phase peak-current variation, and transient decay. Because the original high-resolution recorder export, complete channel documentation, and recorder characteristics are no longer available, this comparison is not presented as a unique experimental validation of the nonlinear saturation law or of the detailed nonsinusoidal inrush waveform. A model-level evaluation framework for controlled pre-magnetization is then formulated using peak inrush current, transient decay time, and an energy-based transient severity index. Relative peak-current error and RMSE are retained as waveform-consistency metrics, while the practical interpretation of the severity index is linked to equipment-specific I²t withstand limits. The experimentally anchored model provides a basis for comparative and sensitivity assessment of controlled pre-magnetization in the DSP-100 operating environment. Prototype-level confirmation of controller performance, nonlinear-waveform fidelity, and the influence on associated compensation and filtering equipment remains a subject of further industrial validation.