Time frequency analysis of transient signals

Voltage and current signals during lightning impulse tests on a transformer are treated as non-stationary signals. A new method incorporating signal-processing method such as wavelets and the Fourier transform is proposed for failure identification. It is now possible to distinguish failure during lightning tests as well as chopped lightning impulse tests. The method is experimentally validated on a transformer winding. The wavelet transforms enables the detection of the time of occurrence of switching or failure events. After establishing the time of occurrence, the original waveform is split into two or more sections. A Fourier transform of the individual section is performed. The frequency content of the waveform is analyzed in the various sections