Power transformers, which are parts of the electric power generation, transmission and distribution have high value, are required to provide high service quality, operational reliability and therefore the need to better exploit our assets have motivated service providers to record operating information at all time. A transformer can be operated efficiently if we know its condition parameters and we are able to measure these parameters with the help of the right diagnostic process or use data acquisition systems. The evaluation of measurement result enables us to draw conclusions about the status of the equipment, estimate its expected lifetime and adjust the action level of the protection circuit. We cannot exactly determine for how long transformers will work properly, because it depends on the load and the used accessories in production state. Utilities have discovered how important these diagnostic processes are, because if there is any kind of fatal failure it will probably cost more than the maintenance processes required. The result can be more accurately evaluated if the available set of data contains more results.
My subject was defined by CG Electric Systems Hungary Company. I had to reveal the effect of cooling system methods for the operating costs and transformers’ lifetime. For this purpose I had to read IEC standards to determine the relationship between them but there were not any exact methods to solve this problem. During normal operating conditions, the temperature thermal process is controlled by the cooling system that makes the transformer in a thermal equilibrium. At the beginning of my essay I present cooling system methods and their control devices for various transformers and afterwards I calculate loss of life due to the hottest-spot of a chosen transformer.