What are the two types of transformer oil used in power transformers?

The two types of transformer oil used in power transformers are mineral oil and synthetic ester. Mineral oil is derived from refining crude oil and is widely used due to its cost-effectiveness and good insulating properties. Synthetic ester, on the other hand, is derived from organic acids and alcohols, offering superior fire resistance and biodegradability, making it an environmentally friendly alternative for transformer oil in power transformers.