Characteristic analysis of zero-mode inrush current of high-impedance transformer

In recent years, zero-sequence overcurrent protection misoperated frequently when the high-impedance transformers are energized without load. This paper studies the characteristics of zero-mode inrush current of the high-impedance transformers, including amplitude and attenuation. Firstly, the corresponding relation of “winding arrangement - flux distribution - equivalent circuit parameters” of transformer was clarified. On the basis of analyzing single-phase and three-phase inrush current, the analytical expression and equivalent circuit of zero-mode inrush current were proposed. Then, according to the different winding arrangement, the different parameters of hollow inductance, self-leakage inductance and saturated mutual inductance of the high-impedance transformers and ordinary transformer were explained and calculated. Further, based on the different parameters and analytical expression, the zero-mode inrush current characteristics of high-impedance transformers were analyzed. The correctness of characteristic analysis of high-impedance zero-mode inrush current was verified via digital simulations and dynamic physical simulations tests.