CALCULATION AND HARMONIC-ANALYSIS OF TRANSIENT INRUSH CURRENTS IN 3-PHASE TRANSFORMERS

Measurements of transient inrush currents in three-phase transformers offer important data for power system operation and protection. Becaus e three-phase transformers are more widely used in industrial applicat ions than single-phase transformers, the inrush current of the three-p hase transformer is worthy of investigation. This paper proposes a sim ple method, extended from that for single-phase transformers, to inves tigate three-phase transformer inrush currents. Harmonic analysis of t he inrush currents is carried out. Various structures of three-phase t ransformers, including winding connections and loading conditions, are discussed. The simulation results are compared with experimental resu lts. 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.