is there oil inside a transformer?

Yes, transformers often contain oil, specifically mineral oil, which serves multiple purposes. The oil acts as an insulator, preventing electrical breakdown between the windings and core, and it also dissipates heat generated during operation, helping to maintain optimal temperature levels. Additionally, the oil can help to prevent moisture ingress, which can degrade the transformer’s performance and lifespan. Some transformers use alternative insulating fluids, but oil is common in many designs.