Determination of a new model to study ultra-saturation phenomenon during the loaded power transformer energization and its effect on differential protection

One of transient phenomenon that causes the mal-operation of the power transformer differential protection during the energization of a loaded power transformer is the ultra-saturation phenomenon. In this paper, a new model for investigating the ultra-saturation phenomenon during the energization of a loaded power transformer is presented and its effect on the differential protection of the power transformer is considered. In this model, the nonlinear characteristic of the power transformer core, the effect of current transformers, and the core losses of the power transformer are taken into account. It is assumed that the load of the power transformer is a resistive and inductive load. Also, the effect of the residual flux and inception angle on the ultra-saturation phenomenon are investigated. In this paper, simulation is done by MATLAB software. The differential protection of the power transformer must be accurate and fast, so the description of the ultra-saturation phenomena is the first level for preventing of the mal-operation of the differential protection. The outcomes of this research can further be used as hints for substation operation personnel as well as for the development of new protection stabilization criteria, which is not discussed further in this paper.