What are standard dissolved gas analysis limits for transformer oil?

DGA “limits” are usually applied as guidance bands rather than a single universal pass fail value, because they depend on transformer type, age, loading history, and oil volume. Standards and guides such as IEEE and IEC methods classify gases and rate severity based on concentrations and trends, focusing on key fault gases like hydrogen, methane, ethylene, ethane, and acetylene. Interpretation emphasizes trending and ratios, not just one snapshot.