. Hermetic transformers
The construction of this type of transformers is such that the oil 

Hermetic transformers
The construction of this type of transformers is such that the oil has no connection with the outside air and the change in oil volume due to temperature changes is compensated in two ways:
- Compensating the increase in oil volume due to the elasticity of the tank with a convex wall.
- The use of a radiator tank with solid walls, where part of the upper space of the tank is filled with an inert gas such as nitrogen, and the change in volume and pressure of this gas compensates for the change in the volume of transformer oil.