Influence of Dissolved Oxygen on the Gassing Tendency of Biodegradable Insulating Liquids Under Thermal and Electrical Faults

Dissolved gas analysis (DGA), widely used for fault diagnosis, can be significantly influenced by the presence of oxygen. Oxygen not only accelerates fluid degradation but also alters the type and concentration of fault gases generated, potentially leading to misinterpretation of transformer conditions if conventional DGA models are applied uncritically. This study investigates the impact of dissolved oxygen on the gassing behaviour of two chemically distinct biodegradable insulating liquids, bio‐based hydrocarbons and synthetic esters, under controlled thermal and electrical stress conditions. Initial oxygen concentrations were systematically varied before subjecting the fluids to laboratory‐simulated faults, including arcing and thermal ageing via localised heating cycles. Post‐fault gas profiles were analysed using standard DGA methods, including Duval's triangle and pentagon, to assess diagnostic relevance. The results reveal a strong correlation between dissolved oxygen levels and gas generation, emphasising the need to adapt traditional DGA interpretation frameworks to account for the oxidative sensitivity of biodegradable fluids. These findings provide critical insights for more accurate fault diagnosis and asset management in transformers employing alternative insulating liquids.