A new algorithm for three-phase power transformer differential protection considering effect of ultra-saturation phenomenon

One of transient phenomenon that leads to the false trip of the power transformer differential protection during the energization of a loaded power transformer is the ultra-saturation phenomenon. In this paper, at first a new algorithm for three-phase power transformer differential protection considering effect of the ultra-saturation phenomenon is presented.To model the ultra-saturation phenomenon, the nonlinear characteristic of the transformer core and the effect of the saturation of the current transformers are taken into account. It is assumed that the load of the transformer is a resistive and inductive load. In this algorithm, the ultra-saturation phenomenon, external and internal faults of power transformer and magnetic inrush current are simulated and appropriate criteria using signal harmonic components of differential currentwill be presentedfor distinguish between these phenomenon by DiscreteFourier Transform (DFT) algorithm. In this paper, simulation is done by PSCAD and MATLAB programs.