Degradation Of Oil Impregnated Cellulose Board Due To Surface Discharges: Experimental Results With Some Theortical Considerations

Oil-pressboard is commonly used in power transformers, due to its excellent dielectric properties, coolingand mechanical support. Surfacedischarge (SD) at oil-pressboard is the type of partial discharges (PD).Previous experimental studies was generally on the formation of carbonization marks along oilpressboard interface due to the surface discharge and the changes in partial discharge behaviour of oil-pressboard samples due to moisture [1], [2]. However, research into the breakdown mechanism of pressboard and change in apparent charges (pC) has not widely reported. The aim of this paper is to investigat the formation of surface discharges in oil pores and parallel fibre region of pressboard using needle plane electrode and some measurements, viz., partial discharge inception voltages (PDIV), apparent charges (pC), and PD patterns (Φ-q-n). In addition to that influence of relative oil absorption of pressboard with surface discharge has been studied. Cellulose board insulations are based on schematic structure of fiber matrix [3].