In the field of power system asset management, few diagnostic methods are as decisive and revealing as Dissolved Gas Analysis (DGA).
Although a transformer operates silently, it continuously communicates its internal condition through the gases produced during electrical and thermal stresses.
These gases dissolve into the insulating oil where they can be measured, trended, and interpreted. For those who know the language, the transformer is never truly silent.
This is why DGA remains the most reliable early-warning indicator of developing faults in oil-filled power transformers. The asset manager who is fluent in its interpretation gains the ability to intervene before failure, optimize maintenance, and extend transformer service life.
Why Transformers Produce Dissolved Gases
Transformers contain cellulose-based solid insulation and mineral insulating oil. When exposed to heat, electrical discharge, or chemical degradation, these materials break down and release gases. The type and concentration of these gases are directly related to the severity and nature of the internal fault condition.
Common Dissolved Gases:
| Gas | Primary Source / Indicator |
| Hydrogen (H₂) | Partial discharge / electrical stress |
| Methane (CH₄) | Low-temperature thermal degradation |
| Ethane (C₂H₆) | Medium-temperature thermal degradation |
| Ethylene (C₂H₄) | High-temperature thermal degradation |
| Acetylene (C₂H₂) | High-energy arcing (critical fault) |
| Carbon Monoxide (CO) & Carbon Dioxide (CO₂) | Decomposition of paper insulation |
The patterns and rates of gas generation are often more diagnostic than individual values. A single DGA reading provides a snapshot; trend analysis reveals progression.
Interpreting the Silent Language
Multiple internationally recognized diagnostic frameworks exist to interpret gas ratios and concentrations:
- Key Gas Method
- Rogers Ratio Method
- IEC 60599 Gas Ratio Interpretations
- Duval’s Triangles and Pentagon Methods
- IEEE C57.104 Condition Limits
The correct method depends on:
- Transformer type & historical operating profile
- Rate-of-change trends
- Load and temperature conditions
- Oil preservation system (sealed, N₂ blanket, or free-breathing)
- Online DGA analysis provides continuous monitoring and early detection
A well-structured interpretation strategy follows:
- Identify total combustible gas (TCG) level — determine condition class.
- Analyze key gas generation trends — identify the type of fault (thermal, PD, arcing).
- Apply gas ratio or Duval interpretations — classify specific fault zone.
- Correlate with load, temperature, and event history — confirm diagnostic validity.
- Determine action: continue monitoring, schedule maintenance, or remove from service.
The Value to the Asset Manager
The true value of DGA lies in risk-based asset decision making:
- Prevents catastrophic transformer failures
- Reduces unplanned outages
- Extends transformer insulation life
- Supports budget prioritization
- Enables targeted maintenance rather than blanket intervention
In power systems where ageing assets, constrained budgets, and operational demands intersect, fluent interpretation of dissolved gases becomes not only useful, but essential.
Conclusion
DGA is the language of internal transformer condition. Mastery of this language elevates asset management from reactive maintenance to predictive, strategic stewardship of critical infrastructure.
Need Assistance with DGA Interpretation or Asset Condition Strategy?
We provide:
- Expert DGA report interpretation
- Failure mode classification
- Risk-based maintenance planning
- Guidance on online DGA monitor selection and specification
Contact us to discuss your transformer fleet needs.
Email: powertransformerhealth@gmail.com