AC Partial Discharge Characteristics in Ester Oil/Pressboard Composite Insulation System with Metallic Protrusion

The presence of sharp-edged metal protrusion in the oil insulation system causes electric field concentration, which lowers the partial discharge inception voltage (PDIV). Many reports have been published on the metal protrusion issue in mineral oil (MO), while few reports on the same issue for ester oil (EO) composite systems. This paper studies AC PD characteristics in an EO/pressboard (PB) composite insulation system with metallic protrusion varying its length and the oil gap. As a result, it was found that the PDIV was determined by the electric field at the tip of the metal needle irrespective of the oil.