According to SKM’s study, the average economic life span of a power transformer ranged from 45 - 50 years. However, this estimate is for a power transformer used in a transmission system only and not for transformers used in power plants or in distribution substations. Transformers in transmission system is always lightly loaded to comply with the n-1 contingency. And of course, proper maintenance practice on the transformer should also be assumed. The amount of loading and proper maintenance greatly affect the life of a transformer.
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