Prediction of power transformers lifetime using thermal modeling analysis

Transformer is one of the main components in distribution system of electrical power system towards the consumers, thereby any damage to the transformers will hinder the distribution of electricity towards the consumers, and in turn will make the SAIDI and SAIFI levels go up. High temperature in transformers can cause degradation in the insulation of transformers which in turn will cause failure in transformers. When the temperature in winding reaches or goes beyond the limit of 110°C, a degradation in insulation will start happening and the remaining life of transformers will decrease. Damage in transformers will cause disturbance in electrical power system and result in a major economic loss. Before damages occur, transformers need to be changed up until it is deemed to be no longer efficient, this can be done by replacing the transformer that is about to be damaged. To predict when a transformer is about to break, a calculation is made based on thermal modelling according to IEEE Std C57.91-1995 with its most prominent variable being Hot Spot Temperature (HST). HST is obtained by MATLAB programming using Annex G of IEEE Std. C57.91-1995. By obtaining HST, thus the remaining lifetime of transformers can be predicted. This study analysed the effect of loading, hot-spot temperature, and ambient temperature on the remaining lifetime of a transformer. The higher those three factors, the quicker the transformer will break, with loss of life percentage increasing exponentially. The highest loading, hot spot temperature, and ambient temperature given in this research gives percent loss of life of 0.0888332%, 0.0193394%, 0.020753% respectively.