A method to identify inrush currents in power transformers protection based on the differential current gradient

This paper presents a new methodology for distinguish between inrush currents and internal faults based on the differential current gradient. The scheme is based on calculating the differential current gradient vector angles in phases A-B-C at all points of the data window. Using statistical calculations, the inrush current is then identified, because its gradient vector behavior will be different in the case of a short circuit occurrence. The method effectiveness has been verified in several computational simulation cases using EMTP/ATP and MATLAB®, analyzing situations of internal faults and inrush currents, including cases of sympathetic inrush in a power transformer, presenting highly satisfactory results.