What role does transformer dielectric oil play in insulation performance?

Dielectric oil provides the primary liquid insulation between energized parts, supporting higher electric field stress than air while also suppressing internal arcing by quenching and cooling hot spots. Its electrical properties (BDV, dielectric dissipation factor or power factor, resistivity) determine how well it prevents breakdown. Oil also impregnates paper insulation, and the combined paper oil system is what ultimately governs dielectric reliability under impulse and AC stress.