Partial discharge distributions in liquid dielectrics

Different dielectric fluids used in HV electrical components were subjected to AC stresses, and the partial discharge (PD) spectra produced under nonuniform and uniform field conditions were recorded with the help of an electrical detector and a multichannel analyzer (MCA) as a function of applied stress. The analysis of the collected data confirms that PD activity in a liquid is a random phenomenon as well as a breakdown process. The presence of PD may be related with the presence in the liquid of bubbles near the electrode interface and with a low density region (vapor phase), which is the first step in the breakdown development. This confirms that PD occurs only in a gas and not in a solid or liquid. In this paper, which is part of an ongoing research project, it is shown that MCA can be a helpful tool in PD measurements and analysis, allowing the demonstration of how the partial discharge inception voltage (PDIV) significantly changes according to the adopted inception criteria.