# DGA 101: Using Dissolved Gas Analysis to Diagnose Solid Insulation Health > Source: > Published: 2026-06-14 20:16:01+00:00 For asset managers and equipment engineers, mastering Dissolved Gas Analysis (DGA) interpretation is essential, because gases like carbon monoxide and carbon dioxide are the first chemical signals that a transformer's solid cellulose insulation is overheating and degrading. Your transformer can talk, and if you know how to listen, you will hear it. Inside every oil‑filled power transformer, a silent story unfolds as the oil and paper insulation bear the brunt of electrical stress, thermal cycling, and aging. When problems begin, the transformer does not send an email or flash a warning light, but it does leave chemical clues dissolved into the insulating oil. Learning to read those clues through DGA separates guesswork from certainty and reactive maintenance from preventive action. DGA is a non‑intrusive diagnostic technique that measures the types and concentrations of gases dissolved in transformer insulating oil. When electrical or thermal stress affects the insulation system, the oil and solid materials decompose, generating measurable concentrations of key gases. Different fault conditions produce different gas fingerprints, and by identifying which gases are present and in what quantities—and by tracking how those levels change over time—you can detect incipient faults while the risk of damage is still low. Modern DGA can be performed offline through periodic laboratory sampling, which typically measures a broader range of gases, or online using continuous on‑tank analyzers that provide real‑time multi‑gas monitoring. For critical assets such as generation step‑up transformers, transmission assets, and distribution transformers serving essential loads, online DGA delivers the greatest value by giving continuous visibility into developing issues. Not all fault gases are created equal, and each key gas tells a different story about transformer health. Hydrogen is produced by low‑energy faults like partial discharge, indicating corona effects or developing insulation problems. Methane and ethane point to low‑temperature thermal faults from overheating components or connections. Ethylene signals high‑temperature thermal faults above 300 degrees Celsius, and the ratio of ethylene to ethane helps identify temperature ranges. Acetylene, one of the most critical indicators, comes from high‑energy arcing faults above 1000 degrees Celsius, and even small concentrations suggest severe electrical stress requiring immediate attention. Carbon monoxide is produced specifically by the decomposition of cellulose paper, indicating thermal stress on solid insulation materials. Carbon dioxide also comes from cellulose decomposition and normal aging, and when interpreted alongside carbon monoxide, it helps assess overall insulation aging. When the paper insulation overheats, even before catastrophic failure occurs, these carbon gases begin to form, making them your primary window into solid insulation health. Moisture accelerates the process, as high water content in the oil increases cellulose aging and raises CO and CO₂ production while also lowering dielectric strength, making partial discharge more likely. Reading a DGA report requires more than glancing at parts‑per‑million numbers. Experienced professionals use structured interpretation methods recommended in industry standards such as IEEE C57.104 and IEC 60599. The key gas method identifies the primary gas and relates it to a specific fault type: hydrogen points to partial discharge, acetylene indicates arcing, ethylene signals high‑temperature thermal faults, and CO points to cellulose decomposition. The Duval Triangle method plots the relative percentages of methane, ethylene, and acetylene into a triangular diagram, and the region where the point falls categorizes the fault more precisely than any single gas can. Ratio methods such as Rogers ratios or IEC ratios analyze pairs of gas ratios to identify fault type and severity, helping distinguish low‑temperature thermal faults from high‑temperature ones and electrical discharge from thermal degradation. Most importantly, trend analysis is essential: never make a major decision based on a single sample. Gases with rising values are far more critical than high but stable levels, and long‑term DGA trend monitoring has been shown to successfully detect progressing faults, enabling timely preventive maintenance before failure occurs. For equipment engineers responsible for specifying, procuring, or maintaining power transformers, there is a practical way to apply DGA insight. Start by establishing a baseline from factory tests and commissioning oil samples, because without a baseline you cannot identify meaningful change. Sample consistently so data remains comparable, and if possible use online DGA systems to capture fine‑grained patterns that periodic sampling might miss. Watch rates of change, not just absolute levels: a transformer with gases above the 90th percentile may operate safely for years, while another with lower concentrations could be developing a serious problem. Consider operational context, as load cycling, ambient temperature changes, and recent maintenance can all affect gas levels independent of fault conditions. And always confirm before acting: never make a major decision based on a single sample. Use confirmation sampling to validate findings before scheduling internal inspection or ordering repairs. A confident diagnosis typically requires combining DGA data with operational history, electrical tests, and physical inspections. Dissolved Gas Analysis is the single most powerful diagnostic tool available for assessing transformer health while the unit remains in service. Understanding what each gas means—and especially recognizing that CO and CO₂ are your primary indicators of solid insulation condition—directly impacts how you specify, procure, and maintain your transformer fleet. This is the kind of practical, industry‑ready knowledge that separates theory from application. Mike has worked for many years in the power utility industry, holding various engineering roles and teaching engineering concepts to the public, to fellow engineers, and to power line professionals. He knows firsthand that much of what you truly need to succeed in this industry is not taught in universities, and that even within utility companies, knowledge often remains siloed within individual teams. The Electrical Transformers Fundamentals video course is Mike's answer to that gap. It takes you from core fundamentals all the way to practical procurement and installation knowledge that would otherwise take years to acquire on the job. If you are an equipment engineer, a utility professional, or someone on the vendor side who needs to communicate transformer specifications and conditions clearly, this course gives you tools that work in the real world. Start your journey today by visiting [Mike's list of courses](https://putilityboard.github.io/#/course).