Oil-filled power transformers are among the most critical and expensive assets in the electrical grid. When they fail unexpectedly, the costs go far beyond equipment replacement: extended outages, safety risks, and disrupted operations. Dissolved Gas Analysis (DGA) is one of the most effective tools available for catching problems before they escalate into failures.
What Is DGA?
Transformer insulating oil serves two purposes: it cools the transformer and insulates internal components. When a transformer experiences electrical or thermal stress, the oil and paper insulation break down at the molecular level, releasing small amounts of gas. These gases dissolve into the oil, and by sampling and analyzing that oil, technicians can identify not just that a fault is developing, but often what kind of fault it is.
The Key Gases and What They Indicate
Each fault type tends to produce a distinct gas signature:
- Hydrogen (H₂) – Often the first gas to appear; associated with partial discharge (corona) activity.
- Methane (CH₄) and Ethane (C₂H₆) – Typically linked to low-temperature thermal faults.
- Ethylene (C₂H₄) – Rises with higher-temperature thermal faults, often involving oil overheating.
- Acetylene (C₂H₂) – A red flag gas; its presence usually points to arcing or very high-temperature faults, and even small amounts warrant immediate attention.
- Carbon Monoxide (CO) and Carbon Dioxide (CO₂) – Indicate breakdown of the cellulose (paper) insulation, which is a strong indicator of aging or thermal stress on the solid insulation system.
How the Data Is Interpreted
Raw gas concentrations alone do not provide a complete picture of transformer condition. MVA’s transformer oil experts apply proven interpretation methods to evaluate results and identify the potential fault type and severity, including:
- Key Gas Method – Identifies the dominant gas associated with a fault type.
- Rogers Ratio and Doernenburg Ratio Methods – Use ratios between specific gas pairs to classify fault conditions.
- Duval Triangle – A widely used graphical method that plots methane, ethylene, and acetylene proportions to pinpoint fault type with strong reliability.
Trending is just as important as any single test result. A gradual, steady increase in a gas over months may simply reflect normal aging, while a rapid spike, even to a seemingly modest concentration, can signal a fast-developing fault that needs urgent investigation.
Why DGA Matters for Asset Management
Used consistently, DGA allows utilities, municipalities, and other power utility and industrial operators to:
- Detect faults such as overheating, arcing, and partial discharge long before they cause visible damage or outages
- Prioritize maintenance and inspection resources based on actual condition rather than fixed schedules
- Extend transformer service life by catching problems while they’re still manageable
- Reduce the risk of catastrophic, unplanned failures
- Support data-driven decisions about repair, retrofilling, or replacement
Best Practices
DGA is most valuable when it’s not a one-off test. Establishing a routine transformer oil testing, and increasing frequency when gas levels or trends raise concern, turns DGA from a diagnostic snapshot into an early-warning system. Pairing DGA with other tests (moisture content, furan analysis, power factor testing) gives an even more complete picture of transformer health.
Request a quote today to have MVA’s transformer oil experts test, analyze and interpret your results.