Assessment of stator winding insulation degradation in large generator by ultra-wideband PD detection

Partial discharge (PD) can be used to study degradation processes of insulation by looking into the physics of the discharge process. This can be done by different means but a valuable technique, at least for the laboratory, is the use of ultra-wideband (UWB) PD detection systems. The UWB PD detection technique is introduced to measure the PD pulse wave of stator bar specimens during multi-stress aging tests. The data obtained are analyzed using joint time-frequency analysis (JTFA) methods, that is, short-time Fourier transform (STFT), discrete Wigner distribution (DWD) and discrete Gabor spectrogram (DGS), and finally Gabor spectrum is selected to analyze the characteristics of a single PD pulse wave. The results show that the UWB method can be used to measure a single PD pulse. The UWB PD pulse wave and its time-frequency spectrogram can indicate the degradation processes of the stator winding insulation in a large generator.