Analysis on the influencing factors of transformer sympathetic inrush current

Closing a transformer without load will lead to the emergence of sympathetic inrush current in adjacent transformer. Sympathetic inrush current always causes mal-operation of protective relay and harmonic over-voltage. Based on simplified equivalent circuit of two shunt-wound transformers, the magnetic analytical expression and rule of bias magnet attenuation are analyzed. After that, the reasons of sympathetic inrush current generation are illustrated. The effects of initial close angle, system resistance, load of transformer, shunt-wound capacitors, residual flux linkage connection in series and manner of grounding to sympathetic inrush current are then analyzed deeply. The conclusion is validated using emulate program. The conclusion of this paper is valuable in estimating the reasons of sympathetic inrush current and eliminating it.