Optimal Rating of A Transformer for a Growing Load Diagram

An optimally rated transformer is defined as one which satisfies all the engineering requirements and also yields a minimum cost over its operating lifetime. This paper develops a cost function which finds the optimal rating of a transformer for a given load diagram. In the case of a load diagram which grows annually, the cost function also forecasts a replacement date when it will become more economical to replace an existing transformer with a larger one in order to obtain a global minimum cost. The results of some case studies are presented and evaluated, and the lifetime cost of an optimally rated transformer is compared with that of a transformer rated according to a loading guide.