On the use of acoustic signals for detection and location of partial discharges in power transformers

The objective of this work is to assess the efficacy and reliability of a certain technique of acoustic emission measurement for detection and location of partial discharges in power transformers. The possibility of locating a simulated partial discharge was studied in the laboratory. The experimental setup involved an arrangement of increasing complexity, starting with a simple tank filled with insulating oil, up to simulation of an unenergized transformer. It was concluded that, under careful control of experimental parameters, such location is effective. The study was complemented with observations on transformers in the field. In this case, results were less reliable. While the acoustic emission test was not sensitive to intense discharges within the internal winding of a transformer, problems in two tap-switches and one mechanical problem were detected. Considering that the literature reports doubts on the effectiveness of the technique, it was found that measurement of acoustic emission is useful for defects external to the transformer winding. Taking into account its success in locating some kinds of defects, partial discharge measurements by both acoustic and electromagnetic means supplement other usual tests to increase the reliability of the final diagnosis