Application of UHF method for partial discharge source location in power transformers

This paper presents a theoretical study relating to partial discharge (PD) source localization in high voltage power transformers using UHF technique. It also includes a brief review of typical PD sources, continuous UHF-based monitoring system, and some suitable UHF sensor types. Using MATLAB calculations and some basic assumptions, the differences in potential accuracy of PD source location are shown for different numbers of sensors, including the influence of sensor position. In addition, in the case of four UHF sensors, other effects were taken into accounts such as background noise sources, signal attenuation, multivariate wavelet denoising and the first peak detection method. By using the programs, at first, it is shown how to find the corresponding loci on which a PD source can be expected to lie by means of two and three UHF sensors in power transformers. Furthermore, using four sensors, it is presented on two different examples how simulated UHF signals, which travel from the partial discharge source to individual UHF sensors, can be used to find a partial discharge source position with sufficient accuracy. Multivariate wavelet transform was applied to the simulated signals in order to remove noise from the signals, and thus to reduce a localization error. The first peak detection method was applied to two various presumed shapes of UHF signal, in order to find time differences of arrival between related signals at the sensors. The corresponding results of partial discharge source location were analyzed and compared.