What is the acceptable BDV value of transformer oil in service?

Acceptable BDV depends on the standard test method, voltage class, and utility acceptance criteria. New oil typically must meet higher BDV values, while in service oil may be accepted at lower values if other indicators are healthy and the transformer is not at high risk. Utilities set thresholds to trigger filtration or drying when BDV drops below a defined limit. Because BDV is highly sensitive to sampling and moisture pickup, the most practical approach is comparing against your utility specification and trending each unit’s results over time to detect deterioration.