Study of the life consumption of distribution transformers and assessment of end-of-life criteria

It is generally accepted that the reliability of power transformers decreases with the ageing of their insulation system. This ageing is due mainly to the thermal degradation of the mechanical characteristics of the insulating materials. Therefore, the Municipal Energy Board of Turin decided to assess the thermal ageing of the whole population of their 6 kV transformers and to base the criteria for transformer selection on the degree of ageing reached by the single units. The authors present the study made for the above purpose. The approach used was both theoretical (loss of life calculations) and experimental temperature rise tests, dielectric tests and short-circuit tests