What is the function of radiator in power and distribution transformer?

Radiators are used in a transformer to cool the transformer oil through natural air or forced air flowing in these radiator fins. As the transformer oil temperature goes down due to cooling it goes to the transformer tank from bottom ,cool the windings and gets heated, and then returns to the radiator for next cooling .This cycle repeats as the oil flow is also natural due difference in temperature of oil on bottom and top.

In big power Transformers this oil circulation is forced by oil pumps for effective cooling.

The radiator has many small fins and there are 4-10 radiator banks in a transformer depending on capacity and make of the transformer.