America’s grid upgrade hinges on a 400-ton machine designed in the 1800s — and just one U.S. mill makes the special steel inside it

Demand for generator step-up transformers, the equipment linking power plants to transmission grids, nearly tripled between 2019 and 2025, straining a U.S. supply chain that depends on a single domestic mill for the specialized steel used in the roughly 400-ton machines. The transformer's core design dates to the 1800s, and the limited number of American steel producers capable of making the required grain-oriented electrical steel has become a bottleneck for grid upgrades. The concentration matters because utilities need the transformers to connect new generation, including renewables, to the transmission network.