Calculation and harmonic analysis of transient inrush currents in three-phase transformers

Abstract

Measurements of transient inrush currents in three-phase transformers offer important data for power system operation and protection. Because three-phase transformers are more widely used in industrial applications than single-phase transformers, the inrush current of the three-phase transformer is worthy of investigation. This paper proposes a simple method, extended from that for single-phase transformers, to investigate three-phase transformer inrush currents. Harmonic analysis of the inrush currents is carried out. Various structures of three-phase transformers, including winding connections and loading conditions, are discussed. The simulation results are compared with experimental results. The proposed method is simple and effective for transformer banks and five-limb transformers. The harmonic analysis of inrush currents is useful for protective relay design.