Radiator is a bank of hollow pipe line which is used to transfer the thermal energy from one medium to another for the purpose of cooling. Some Bank are used at the power transformer for cooling the transformer oil as well as reduces the winding temperature under loading condition. The radiators are connected to the transformer through pipe line at upper and lower side of the transformer which is shown in fig.
When the transformer is under loading condition, the transformer will be heated enormously and that heat has to be reduced under limited value otherwise the transformer may me damaged due over heating. We can easily reduce the temperature of the transformer by applying radiator bank.Now , we describe how it is reduce the temperature of transformer oil . As per convection heat transfer law, warm oil increases in volume and comes to the upper portion of the main tank and this heated oil enters in the radiator through top valve and cools down by dissipating heat through the thin radiator wall. This cold oil comes back to the main tank through the bottom valve. This cycle is repeated continuously till the load is connected to the transformer. Dissipation of heat radiator can be get faster by force air provided by means of fans. At higher ratting transformer( i.e <= 50 MVA Tr.), an oil pump may be used for speeding up oil circulation.