The UHF PD measurement method is usable as stand-alone measurement and as a supporting measurement for off- and on-line PD detection. The sensitivity of UHF PD measurements is sufficient and is normally not affected by external disturbances. Especially in noisy surrounding it might be a very helpful method to support other PD measurement techniques for example dissolved gas analysis and acoustic location of PD.

The paper presents the experience using a combination of different partial discharge (PD) measurement methods both to detect PD in power transformers and to improve interpretation and localisation of their sources. The multi-terminal PD measurement is illustrated here using STAR diagrams for discrimination between external noise clusters and multiple internal PD sources. Several different PD sources in different phase windings during an off-line measurement on a power transformer were detected and the UHF method confirmed these results and conclusion.

Partial discharges in (power) transformers are often a predecessor of a serious  fault. For this reason partial discharge measurements are an important diagnostic tool to monitor the insulation condition of a transformer. For on-line measurements, a detection method based on the high-frequency (UHF)  signals emitted by the discharging source is used and can be detected. Moreover, the UHF technique offers the possibility to locate and identify the PD source.

In this paper, the acoustic wave propagation inside the transformer is explored via numerical simulation. Based on the understanding of wave propagation, a novel-structure fiber-optic acoustic sensor array is properly designed and installed into one phase winding, which is from a real 35 kV transformer. Experimental verification shows that, by using this proposed design, PD localization with less than 5 cm error can be achieved.