This study reported the formation of electrical treeing that occur on the epoxy resin insulating material with a thickness of 1 mm. The electrode system resembles a leaf-like sample specimen with a gap between the tip of needle electrode and aluminum tape of 1 mm. The samples were given 1% of the pollutant in the form of ammonia (NH3) with a variation of the conditioning time 12; 24; 48; and 96…