Why are the core and coils of a large capacity transformer typically placed in an oil-filled tank?

The placement of the core and coils of a large capacity transformer in an oil-filled tank is primarily because oil serves as an excellent insulator. In high-voltage applications, the electrical insulation between conductors and other components of a transformer is crucial. The oil fills the spaces between the core and coils, effectively separating conductive parts and preventing electrical breakdown.

Additionally, the oil provides cooling for the transformer. As electricity flows through the coils, heat is generated, and the oil circulates to dissipate this heat, maintaining optimal operational temperatures. This dual function of providing insulation and cooling is essential for the safe and efficient operation of large transformers.

While it is true that oil does help in reducing vibrations and can contribute to energy efficiency, the most critical and direct reason linked to transformer design and safety is its property as a strong insulator in high voltage environments.