The first transformer was built in 1885. Progress for the first century was linear, based more on experience than on science. Improvements included material developments to reduce no-load loss generated in the core and load loss generated in the windings and structural parts. High capitalisation rates used to evaluate cost of ownership have driven materials suppliers to produce very low loss core steels and has encouraged the development of amorphous steel. Measures taken to control load loss have included the fitting of magnetic shunts to provide an alternative path for leakage flux. High reliability in service is a major requirement for power transformer design. New failure mechanisms have been identified that include part-winding resonance, fast-front transients, geomagnetic disturbances and static electrification. These new phenomena must be understood and design philosophies developed to encompass the potential problems. Progress in the second century is science based with the application of rigorous design control procedures to ensure that every innovative change is correctly reviewed to establish the pedigree of the change and foresee all possible ramifications of the change on the transformer in test or in service