Why is dielectric strength of transformer oil critical for preventing breakdown?

Dielectric strength determines the oil’s ability to withstand electric stress without breakdown. High dielectric strength prevents arcing between energized components and grounded surfaces. When moisture, particles, or aging byproducts reduce dielectric strength, localized discharges can occur, leading to insulation failure. Maintaining adequate dielectric strength ensures safe operation under rated voltage conditions and protects solid insulation from irreversible damage.