Wavelet Power Ratio Signature Spectrum Analysis for Prediction of Winding Insulation Defects in Transformer and Shunt Reactor

The reliable analysis for identification of winding insulation defects in transformer and shunt reactor are necessary for power industries during lightning impulse test. In this paper, wavelet power ratio signature spectrum analysis is proposed to identify the short duration of partial discharge (PD) pulses of 170 ns and 30 ns within windings due to impulse voltage excitation. It provides a solution to the problems associated with several random features in the measured winding responses at neutral terminal of the winding due to PD pulse through visual assessment of mutual strength between normal winding response and one with PD response using appropriate mathematical formulation in wavelet transform. In this context, the normalized response due to reduced impulse voltage excitation is formed to be a basis function to identify the PD pulse. If the surge impedance characteristic of the winding is changed due to PD pulse at full wave impulse voltage excitation, then formulated wavelet power ratio signature spectrum analysis will extract the evidence of potentially interesting features through assessment between basis function response and one with PD response. To prove feasibility of the proposed analysis, experimental analysis is performed on a layer winding.