PD recurrence in cavities at different energizing methods

The measurement of partial discharge (PD) activity has become an invaluable tool for monitoring the insulation condition of high-voltage components in service. In particular, it is important for factories and for the utilities to get an indication of the time to breakdown. In this paper, the authors describe a study on the use of a damped ac voltage (DAC) method and a very low frequency (VLF) method to stress insulation and to detect partial discharge activity. The main goal of this study was to find out whether the PD patterns obtained at 50 (60)-Hz voltage correspond to those obtained at either lower frequency voltage (VLF) or higher frequency voltage (DAC). For this purpose, a combined theoretical and experimental approach for dielectric bounded cavities was used. The effect of the frequency and the shape of the voltage (DAC) on the PD phase-resolved pattern were studied in the laboratory. Tests were performed on dielectric bounded cavities in polyester with the DAC method, the VLF method (0.1 Hz), and the 50 (60)-Hz method. Moreover, the PD phenomenon was theoretically analyzed at different stress frequencies, and a comparison was made between theory and measurement.