Why is breakdown voltage testing of transformer oil critical for insulation health?

BDV testing indicates the oil’s ability to withstand electric stress without forming a conductive path. Moisture, particles, and oxidation products can sharply reduce BDV, increasing risk of partial discharge, internal arcing, and insulation breakdown under switching or lightning impulses. While BDV alone does not diagnose fault type, it is a fast indicator of contamination and handling quality. It is especially important after oil filling, filtration, or repairs, because poor cleanliness or water ingress can create immediate reliability risk in high voltage assets.