Wavelet transform based discrimination between inrush and internal fault of indirect symmetrical phase shift transformer

The non-sinusoidal inrush current has high magnitude and hence the discrimination from the other operating conditions such as internal faults becomes difficult in the protection of a power transformer. This paper proposes an effective method based on wavelet transform for the differentiation between inrush current and internal fault current in indirect symmetrical phase shift transformer (ISPST). Conventional Parseval´s theorem has been used to calculate the wavelet energy of the differential current and a suitable threshold is decided for the discrimination between inrush and internal fault condition of ISPST. Different types of internal fault and inrush current conditions under a wide range of switching angle have been considered for the verification of the proposed method in the present simulation study. PSCAD/EMTDC has been utilized as simulation plateform.