DGA is a pattern and trend, not a single-gas verdict
Diagnostic gases support hypotheses about electrical and thermal activity. Sampling integrity, generation rate, operating context and companion evidence determine confidence.
Reviewed Jul 2026 · Oil Testing Atlas editorial teamDissolved gas analysis is powerful because different stresses generate characteristic gas patterns. It is also easy to overstate when a single concentration or ratio is separated from time, loading and sample quality.
Protect the gas sample
Gas-tight sampling, suitable containers, correct flushing and avoidance of bubbles are essential. Temperature, oil handling, leaks and maintenance can create discontinuities in the record.
Sampling oil-filled electrical equipment is safety-sensitive work for trained personnel under approved electrical and site procedures.
Interpret concentrations as a system
Review the full gas pattern, generation rates and changes in operating load. Ratio or graphical schemes are classification aids with applicability limits, not automatic fault diagnoses.
Correlate with oil condition, moisture, dielectric tests, inspections and electrical monitoring. A credible hypothesis should explain the broader evidence.
- Use method-consistent history
- Check whether oil was processed or topped up
- Escalate rapid multi-gas changes to qualified specialists
Keep maintenance decisions qualified
The consequence of a possible transformer fault can be high, but interventions also carry operational risk. Laboratory findings should feed an asset-management process with equipment design, criticality and qualified engineering review.
Current IEC or other contractually applicable guidance should be consulted directly for procedural and interpretation requirements.
Key takeaways
- 01Preserve gas-tight sampling integrity
- 02Trend the complete gas pattern
- 03Use ratios within their applicability
- 04Involve qualified electrical specialists