A large power transformer is generally a high voltage, high MVA unit used in transmission or major substation applications, typically tens to hundreds of MVA and voltage levels from about 69 kV up to 765 kV or more. These transformers step up generator voltage to transmission levels or step down transmission voltage to sub transmission or distribution levels. They are physically massive, oil filled, and equipped with radiators, bushings, on load tap changers and advanced monitoring. Large power transformers are critical grid assets with long lead times, complex transport logistics and high replacement cost.