Partial discharge inception voltages of an inhibited mineral oil in quasi-uniform electric fields

The insulating liquid used in a large power transformer is typically subjected to uniform or quasi-uniform electric fields, however, the majority of the research concerning partial discharge (PD) characteristics of dielectric liquids employs electrode systems generating highly divergent electric fields so as to facilitate PD inception. This research aims to investigate the PD inception voltage (PDIV) of an inhibited mineral oil under divergent and quasi-uniform a.c. electric fields. In the experiments a plane-to-plane electrode system with an adjustable needle protrusion was used to produce quasi-uniform electric fields. To obtain the PD inception fields (PDIF) under different configurations at the corresponding PDIVs, electrode system models were developed in COMSOL software to simulate the electric field distribution. Results from different electrode configurations suggest that the PDIV of the mineral oil is affected by electrode configuration. But unlike PDIV, the PDIF tends to be independent of electrode configuration. The simulated PDIF of the mineral oil is 1426.4 kV/mm.