Investigation on aging of stator bar insulation based on JTFA of PD pulse waveforms

In the present paper, partial discharge (PD) pulse waveforms of stator bar insulations subjected to various aging factors are investigated by means of extra-high frequency PD measurement technique. The test results indicated that both rising time of PD pulse and pulse width vary with aging time. Although different aging factors, such as electrical, electrical-thermal and thermal-mechanical stresses etc., result in different alteration in PD pulse waveform, it is observed that high frequency components in the time-frequency spectrum of PD pulse waveform add with aging time in all of specimens by joint time- frequency analysis (JTFA). If high frequency components in dispersion appear in JTFA spectrum, it is though that oxides with low-molecule weight are produced due to PD in the void and acidic matter deposited on the surface of dielectric around the void erodes the dielectric and results in electrical tree spreading out.