Changes of copper losses during the service of distribution transformers

This paper is part of a series of articles concerning the changes of losses in transformers as result of extended exploitation. The paper discusses and analyses the obtained loss values of 199 pcs. network transformers after a long service life. The aftermath obtained evidently represent an raise in the measured costs an electrical energy the tabulated values. The factors that affect the increased losses are illustrated for the two main types of transformer coil, according to the shape of the conductor, which are respectively introduces in operation in the period up to 1999 and beyond until 2022. The augmentation of losses over a period of 5 years r% are calculated according to the least squares model. Through the statistical values collected over the years, a method for determining the losses in copper is presented and approximating mathematical function is given. The presented analysis demonstrates a good precision of the model.