An overview of liquid filled, dry type and GSU transformers

On the distribution level (transmitted power up to 10MVA) there are two main categories of distribution transformers: liquid filled (using mineral oil or replacement fluids such as synthetic or natural esters) and dry type. The liquid filled transformers are the most compact and cost efficient solution, whereas dry type transformers are preferred in environments where fire safety is of special importance such as, for example, underground substations, mining sites, marine and some industrial applications. Standard versions of distribution transformers are cooled passively as the heat generated by losses is transported away from the core by natural convection of the insulation medium. In the case of liquid filled products, this heat is then transported through the tank walls by thermal conduction and removed by the natural or forced convection of air. Dry transformers in closed environments usually have a forced internal convection flow of air to ensure sufficient cooling of the transformer core.