Identification Of Inrush Current In Power Transformer Differential Protection

In power transformer differential protection the major concern is to successfully identify the magnetizing inrush current.In this study,an approach of discrimination between internal faults and inrush currents based on discrete wavelet transform is proposed.The wavelet transform is applied to decompose the differential currents into the details coefficients in several levels of frequency bands;it is observed by inspecting different inrush and internal faults cases,a fault condition is the most probable if a remarkable change in detail coefficients is noticed.This fact is utilized in order to establish a diagnosis criterion,where the relative wavelet energy is defined as a characterizing quantity to extract the distinctive features of the various transient events.The discrimination criteria is based on the energy variation amount,which is monitored comparing the values of the relative wavelet energy in two successive time intervals,where an inrush is detected generally when the difference is not a remarkable quantity.To evaluate the performance of the proposed algorithm it is implemented on MATLAB platform and different transient cases are simulated.