How does DGA analysis of transformer oil indicate internal faults?

DGA indicates internal faults by identifying which gases are present, their concentrations, their growth rates, and their ratios. Different fault mechanisms crack oil and paper differently, creating characteristic gas patterns. Analysts compare results to historical data for the same transformer, typical limits for similar units, and ratio methods that classify likely fault types. Sudden rises or persistent growth trends are often more important than a single high value, because they show active fault progression.