Localization Accuracy of Partial Discharges in Power Transformers

Power transformers belong to the most expensive and strategically important components of any power generation, transmission and distribution system. Therefore their reliability is of key importance. An increased electrical field in a region of weak insulation can generate permanent partial discharge activity (PD) in the insulating system which may finally lead to a complete electrical breakdown. Due to the high safety factor of the design, dangerous defects normally need some time to cause an alarm or fatal failure of the transformer. Defects caused by electrical stress are detectable by sensitive PD measurements [1]. It is generally accepted that PD detection using electrical and/or acoustic techniques, is one of the most effective diagnostic method to reveal local PD defects [2]. Although PD measurement is suitable to detect local defects, the localization of PD-sources in the large power transformer is still a challenge for all testing engineers. All PD-sources hidden deep in the insulating system, which are the most dangerous one, are not detectable in a correct way at bushings due to the attenuation and reflection phenomena on the way through the capacitive and inductive network of the insulating system of the transformer [1]. To locate PDs in power transformers effectively and quickly with the best accuracy, to locate more than one PD source in a single power transformer by analyzing several single-shot signals and to investigate the effects of noise (corona) on acoustic localization are the motivation of this study. They will be implemented in it.