Partial discharge location in high voltage transformers

Partial discharge (PD) location is a common problem within power transformers diagnostics and is important for assessing the severity of any detected fault. The technique presented in this paper is suitable for any type of discharge signal through determination of the predominantly capacitive operating region in the frequency domain of the transformer. Theoretically, any components signal in this frequency region will retain their waveshape and phase without significant attenuation. To obtain the predominantly capacitive region of a transformer winding, the relationship between the bushing terminal and neutral terminal has to be determined. In the predominantly capacitive region the two terminals will have a linear relationship in dB. To obtain the model of the transformer winding under test, it is injected at one end with a low voltage calibrated impulse to determine its initial parameters. Based on the measurement at the bushing and neutral terminals, the linear relationship of the two terminals is found by a fixed distribution equation derived from a lumped circuit parameter model. For verification, experiments within the laboratory have used various artificial PD signals injected at different points along a model winding to represent different PD sources. By considering the relative magnitude of a discharge signal at predominantly capacitive frequencies of the winding it is possible to evaluate the position of the discharge source.