How is dissolved gas analysis in transformer oil interpreted?

Interpretation combines gas concentration limits, rate of change, and diagnostic ratio methods. Analysts review hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, and carbon dioxide, plus total dissolved combustible gases. They compare current results with prior samples, consider load and temperature history, and evaluate whether gases suggest partial discharge, thermal fault, or arcing. Interpretation also accounts for oil type, recent oil treatment, and sampling quality. Final output is usually a fault likelihood and recommended action level.