Experimental Discharge Initiation Study for Paper and Pressboard Insulated Electrodes in Mineral Oil and Synthetic Ester Fluid

Ester insulating fluids have different properties compared to commonly used mineral oils and for application in power transformers adequate design rules are needed. For dielectric design, parameters describing discharge initiation, propagation and breakdowns are relevant and need to be quantified. Some of them are defined and measured within this study. The discharge initiation lightning impulse voltages are measured for two test object types reflecting typical geometries of power transformers construction (oil gap and oil wedge configuration) and for two fluid types (mineral oil and synthetic ester). Furthermore, the discharge delay time is evaluated as well as the nature of discharge propagation.