Calculation of Residual Flux Based on Preisach Model and Entering Phase control of transformer to eliminate Inrush Current

When transformer enters into power system without load form last cutting off, which because of action of protective device in answer to system fault and changes of system framework structure, the residual flux of ferromagnetic-core is of no randomicity. Firstly on the basis of time-character of ferromagnetic material analysis, combined with Preisach model, a way to calculate residual flux is proposed in this paper. After this, an expression between residual flux and entering-phase is educed to eliminate inrush current in single phase transformer, then its rationality has been testified by an EMTP test. Meanwhile, the simulation has discovered some rules between residual flux and the range of entering-phase at a given overshoot limit of inrush current. Finally these rules have been used to propose a control tactic about entering phase in sections to design a device to eliminate inrush current