Analysis and Visualization of Time-Varying Harmonics in Transformer Inrush Currents

Abstract

The accurate measurement of the magnetizing inrush current in transformers is of the greatest interest for the correct operation and protection of power systems. This paper presents a method for analysis and visualization of time-varying harmonics using wavelets and its application to inrush currents in transformers. The Wavelet Packet Transform and the Inverse Wavelet Packet Transform are used as a filter bank for decomposition and reconstruction in the time domain of the harmonics in the inrush current. The peak and the r.m.s. magnitude and their decays, and the time evolution of harmonics in time and frequency domains as a function of the instant of connection of the input voltage to the primary winding are studied in detail. The results obtained can be used for the adequate design of the transformer protection and the selection of the instant of connection of voltage supply to the primary winding.