Transformers have been used in the power industry for more than a century since the widespread use of ac generation, transmission, and distribution became the standard. Even now, they remain one of the most important substation assets that utilities around the world plan and operate. Figure 1 shows a 200-MVA transformer in service at a utility substation. In the past few decades, with a rapid push toward grid digitalization due to the proliferation of distributed energy resources (DER), the age-old transformer asset management strategy has also evolved for the better.