As the population of transformers in service increases and their operating time
extends, much attention has been focused on their availability and reliability. However,
insufficient research work concentrates on how to evaluate transformer’s aging
condition, although huge progress has been made on the techniques of fault diagnosis
and condition assessment of transformer in past decades. This paper presents the
concept of Aging Index (AI), which is a practical tool that combines the results of
routine inspections, and site and laboratory testing to estimate the aging condition of
oil-immersed transformers. Further, frequency domain spectroscopy (FDS) as a novel
non-destructive testing technique to estimate remained life expectancy is included in
aging evaluation system. Moreover, a software system based on transformer’s electrical
and thermal parameters is developed correspondingly, by using a multi-parameters
analytic approach. This system would dedicate to decision-making and replacement
planning and has good application prospects.