Why is power transformers oil tested for dissolved gases and contaminants?

Dissolved gas analysis detects gases generated by electrical and thermal faults, giving early warning before external symptoms appear. Different gas patterns indicate partial discharge, overheating, or arcing. Contaminants like water, particles, and oxidation products reduce dielectric strength and impair cooling, increasing failure risk. By testing for gases and contaminants, operators can prioritize maintenance, prevent catastrophic failures, and extend asset life. Oil tests also validate the effectiveness of filtration, degassing, and sealing repairs. Trending is essential because sudden changes can indicate a rapidly developing fault that needs immediate investigation.