OPTIMAL AGEING LIMIT OF OIL-IMMERSED TRANSFORMERS IN FLEXIBLE POWER SYSTEMS

This paper investigates the choice of optimal ageing limit of transformers in flexible power systems. In contrast to similar studies, the paper considers the remaining calendar life of transformers. Moreover, it is shown that for the same insulation ageing it is possible to transfer a different amount of energy through transformers. Hence, the paper uses a maximal energy transfer as criterion for defining the optimal ageing limit of transformers (both the existing and new ones). Results reveal that the optimal ageing limit for transformers should be equal to the ratio between the remaining insulation life and the remaining calendar life. Moreover, the paper presents the energy transfer through new transformer as function of various ageing limits and different durations of a calendar life. Hence, the choice of ageing limit can differ from traditionally used (normal) ageing limit if system operators consider the ratio between the remaining insulation life of transformers and their remaining calendar life. MATLAB code is available for readers in open access.