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In the world of electrical equipment, oil-filled transformers are true workhorses. Yet, the unexpected issue of hydrogen generation often causes concern. After-sales teams are inundated with questions, customers remain puzzled, and even transformer engineers find themselves scratching their heads. Today, let's dig deep into the root causes of hydrogen generation in oil-filled transformers.
We begin, as always, with the industry compass—DL/T722-2014, Guide for Dissolved Gas Analysis in Transformer Oil. Transformer oil is a mixture of hydrocarbons of various molecular weights. When exposed to electrical or thermal faults, molecular bonds such as C–H and C–C can break—like a stone disrupting a calm lake. This leads to the formation of reactive hydrogen atoms and unstable hydrocarbon radicals. Through complex chemical reactions, these combine to form hydrogen (H₂) and low-molecular-weight hydrocarbon gases. Solid carbon particles and hydrocarbon polymers (X-wax) may also form. In addition, oil oxidation can generate small amounts of CO and CO₂, which accumulate over time.
Curious about how gas generation correlates with temperature? Refer to Figure A.1 in the standard—it offers a valuable window into the internal chemistry of transformers under equilibrium test conditions.
Improper drying of iron components such as the transformer core or tank, or the ingress of moisture from air, can trigger issues. Moisture significantly lowers the breakdown strength of oil-impregnated insulation. Once involved in chemical reactions, it contributes to the formation of hydrogen.
A notable mention is stainless steel—in environments with elevated temperatures and dissolved O₂, certain paints and coatings can catalyze reactions on specific stainless steel surfaces, causing a surge in H₂ generation. Even direct contact between stainless steel and oil can lead to catalytic hydrogen production. Therefore, material selection and precise drying processes are critical.
Aging insulation, poor material quality, or flawed design can raise local temperatures to 120–200°C and trigger partial discharges. These discharges break down insulation materials, causing hydrogen, methane, acetylene, and other gases to be released—turning seemingly calm oil into a latent gas bomb.
Transformer oil can inherently contain dissolved gases. If not fully removed after fault repairs, absorbed gases in the core can slowly release into the oil. Cooling systems may introduce gas into the main tank, and even welding with oil present can cause thermal decomposition and gas generation, leading to spikes in hydrogen levels.
Other subtle factors include high-voltage testing, which induces hydrogen and hydrocarbon gas formation under thermal and electrical stress. These gases cling to solid insulation materials and remain undetected during factory testing. Over time, they gradually desorb into the oil, causing a delayed rise in hydrogen levels. Additionally, metals can absorb hydrogen and release it slowly, explaining why newly installed transformers may initially show high gas levels that later decrease.
Hydrogen generation in oil-filled transformers is like a complex chemical magic show—an outcome of numerous interacting factors. Routine chromatographic analysis of transformer oil and close monitoring of hydrogen and other gas concentrations are essential. Only then can hidden faults be uncovered in time, ensuring reliable transformer operation and safeguarding power system stability—without being caught off guard by an unexpected “hydrogen spike.”
