Dissolved gas analysis identifies patterns of gases generated by electrical and thermal stress inside the transformer. Elevated hydrogen can indicate partial discharges or low energy electrical activity, methane and ethane often point to thermal overheating in oil, and acetylene is strongly associated with high energy arcing. Carbon monoxide and carbon dioxide relate to paper insulation heating and aging. DGA is especially valuable because it can detect developing faults before they cause protective trips. Interpretation uses gas ratios, rate of change, and historical baselines, rather than a single universal threshold.
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