New approaches in arrival time-based PD location in transformers

The diagnostic examination of partial discharges (PD) is regarded a powerful, non-destructive and sensitive diagnostic tool for the condition assessment of insulating systems. Two major tasks of PD measurements may be distinguished, (i) providing evidence of PD (detection) and (ii) the location of the PD. Particularly with regard to the question "Where is the PD source?", the possibility to geometrically localize the flaw, by means of arrival times of the acoustic signals, gets an extremely interesting option. For the estimation of the PD site precise measurements of acoustic arrival times and robust positioning algorithms are essential. The averaging of acoustic PD signals (either with an electric or an electromagnetic UHF PD trigger signal) helps to enhance the acoustic sensitivity. The acoustic detection limit is hence lowered significantly and the determination of the arrival times is made possible for weaker PD. Supplementary steps, like automatic arrival time determination or additional wavelet-based de-noising further improve the overall location accuracy. Regarding the solution algorithms a new approach within the acoustic signal processing, which works with pseudo-times, allows for the use of robust direct GPS (Global Positioning System) solvers instead of the previously used iterative algorithms.