What does a test of transformer oil reveal about moisture, acidity and gas content?

Moisture results indicate how wet the insulation system is and how much dielectric strength margin is being lost. High moisture accelerates paper aging and increases partial discharge risk. Acidity reflects oxidation; rising acidity suggests oil degradation and sludge formation that can block cooling paths. Gas content, especially via DGA, reveals internal fault processes. Hydrogen and methane may indicate low energy overheating or partial discharge, while ethylene and acetylene can signal high temperature faults or arcing. Trends are more valuable than single values.