ABSTRACT
Oil is kept in circulation by gravitational buoyancy in the closed-loop cooling system. As the surface heat transfer coefficient of water is greater than that of air, such a type of cooling results in smaller radiators. This type of cooling is termed water forced cooling. Depending on the type of oil circulation, the transformer cooling system is termed OFWF or ODWF type of cooling. Accurate estimation of temperatures on all surfaces is very critical in the design of transformers to decide the operating flux density in the core and the current densities in the windings/connections. It helps in checking the adequacy of cooling arrangements provided for the active parts and in ensuring reliable operation of the transformer; the insulation life can be estimated under overload conditions and corrective actions can be taken in advance. The values of maximum oil and winding temperatures depend on the ambient temperature, the transformer design, loading conditions and the cooling provided.
