Procedure for identification and localization of dangerous PD sources in power transformers

In case of a detected partial discharge (PD) in new power transformer during the delivery test in the high voltage laboratory, the most important question arises from both the customer as well as from the manufacturer: where is the PD source? In such a situation, additionally to the measurement of apparent charge with a conventional PD-system, detection of acoustical PD signals can be used to localize the PD source. In many cases, especially for hidden PD sources in the solid insulation, or in the main insulation, there are no acoustical PD-signals detectable. To open a transformer for visual inspection without a clear indication about the position of the PD source is not only time consuming but also in many cases without any findings. In this contribution a successful procedure for reliable identification and localization of dangerous PD-sources is described.