Electricity transmission substations are fixed infrastructure assets, and the power transformer is the most visible item of equipment. The technologies embedded in protection and control switchgear, as well as in power transformers change over the very long life of a substation, even though the basic functionality remains the same. Changes in equipment technologies present salient but real challenges in design of electricity transmission networks, and especially on acquisition, operation and maintenance, and disposal of transformers deployed in substations.  In addition to obsolescence, some of the challenges include age-related degradation, as well as increasingly sophisticated loading requirements on substations. A bibliographic search between 1970 and 2014 indicates that new materials plus computer-aided modelling and tools are widely applied to design and manufacture transformers to achieve higher voltage and power ratings, while sensors, information and computing systems technologies and big data analytics are increasing applied to determine transformer health index. Empirical data obtained from a case study utility suggests that operators and maintainers tend to focus on technical health indices, and this raises concern as to the robustness of decisions to decommission, refurbish, replace, and dispose of transformers in electricity transmission substations