Transformers play an important role in the electricity supply, so their high degree of reliability is essential. Their operation during occur losses is being heated themselves. The high temperatures due to deteriorate the quality of oil-impregnated cellulose insulation in transformers so later it can not perform its insulation functions.
The high temperature and the water in insulation are two of the important factors that limit the life expectancy of transformers therefore we have to cool them and prevent water from entering.
In practice heat exchangers are being used for cooling of high power transformers. These heat exchangers are being controlled by automatic cooling which is observing the temperature of oil and in some cases also the winding-temperatures.
This thesis presents convection in transformers and the effect of temperature to insulation and the life expectancy of transformers. After that it finds the optimal operating temperature.
The thesis presents some measurement result and gives a recommendation for setting of automatic cooling for growing the life expectancy of transformers.
As a closing the thesis calculates additional operating costs of more intense cooling.