What characteristics define good transformer oil?

Good transformer oil is characterized by high dielectric strength, low viscosity, and excellent thermal conductivity, which ensure efficient insulation and heat dissipation. It should have a high flash point to minimize fire risk and low water content to prevent degradation. Additionally, good transformer oil exhibits chemical stability, resistance to oxidation, and low pour point to maintain performance in varying temperatures. These properties collectively enhance the reliability and longevity of power transformers.