A new principle of discrimination between inrush current and internal fault current of transformer based on self-correction function

When differential protective relays are applied to transformer protection, how to identify the magnetizing inrush current and short circuit current caused by internal fault is the key problem. Here, regarding the inrush current and short circuit current as the random signal, the sampled data are analyzed by correlation function principle in the digital signal processing (DSP) and the self-correlation function of the sampled data is calculated. Through the similar comparison operation conducted by standard self-correlation function (SSCF) formed with sinusoidal current the short circuit current and the inrush current can be distinguished by the magnitude of similarity coefficient. The results in electrical power dynamic laboratory (EPDL) verify the feasibility of the proposed method