Combining acoustic and electrical methods to locate partial discharge in a power transformer

Partial discharge (PD) measurement on power transformers has become an established approach for transformer insulation diagnostics. Acoustic measurement can be used to detect PD in power transformers. With this technique a detection and localization of PD is possible by placing acoustic sensors on transformer tank surfaces. One advantage of this acoustic approach is it is less subject to electrical interferences. Another advantage of the approach is the possibility of finding the location of the PD source, as the location information is important for understanding the risk and addressing insulation problems effectively. This paper describes the approach to locate the PD source by performing acoustic measurement using piezoelectric sensors with electrical PD measurement signal used as trigger. PD source is located by triangulation based on the distances from the acoustic sensors derived from the time of flight of acoustic signals and signal propagation speed. The time of flight of an acoustic PD signal is estimated as the time delay between a PD signal detected through electrical measurement used as trigger and the acoustic signal captured by the sensor. Nonlinear equations are used to locate the PD source based on the sensor positions, the signal propagation speed, and the signal arrival times. The electrical trigger signal can be generated either conventionally according to IEC 60270 or by using the UHF measurement range. This paper also presents the above mentioned PD source localization approach using a case study.