Phenomenon of Transformer Sympathetic Inrush and Analysis of an Example

Abstract

According to a mal-operation accident of differential protection which is caused by the effect of a switching-on transformer with no load on a parallel running transformer in a 35KV substation, the emergency and the development of transformer sympathetic inrush current was analysed from the aspect of the flux. And the three-phase differential current and their second harmonic component were obtained, which shows that the mal-operation wasn't caused by the low second harmonic component in the differential current but by the changed transfer characteristics of the current transformer, which leads to an increase in the differential current.