Enhanced dielectric AC breakdown strength of polyethylene using voltage stabilizing additives

Abstract: There is currently a need to increase the voltage level in high voltage transmission and distribution systems in order to transmit power in a more efficient way. However, the insulation of the conductor in high voltage alternating current (HVAC) cables needs to be improved in order to withstand these high voltages. One approach to enhance the dielectric breakdown strength, i.e. the threshold value before the insulator becomes conductive, of polymer insulation materials is to use organic molecules with aromatic structures. The aim for this investigation was to increase the dielectric breakdown strength for polyethylene with nine different aromatic additives. The additives where chosen according to physical properties and alkyl chains attached to its aromatic core. The additives where mixed at a certain weight concentration with polyethylene in a Brabender mixer, pressed to a certain thickness and fourteen pieces from these pressed plates where tested with AC breakdown. The result where evaluated with Weibull distribution statistics and compared with polyethylene references that was prepared likewise at the same occasions. Although all the additives showed at some concentration an increase relative to the reference, the concentration of 0,2wt% and 0,5wt% of additive D1 resulted in the highest overall increase in breakdown strength, 7,5% and 8,2% respectively. It was suggested that the relative small increases compared to the published data might be due to the reference’s already excellent insulation properties. The deviated results may also indicate that the enhancements in electrical treeing resistance are not comparable with enhancements in dielectric breakdown strength. However, it was concluded that the reliability of the method was promising and that the Rogowski-shaped electrode generated trustworthy and narrow distributions of results.