Who makes large power transformers (345–765 kv) & substations for AI data centers

The substation and its transformers are the physical interconnect between the utility transmission grid and the campus, converting transmission voltage down to the range that HV switchgear and downstream MV distribution can handle. Everything inside the fence — HV switchgear, MV switchgear and E-houses, transformers all the way down to the rack — depends on this equipment being on site and energized before load can be added. Because a large power transformer is a custom-engineered, long-lead unit built to a specific voltage, MVA, and impedance spec, and because global manufacturing capacity for the core steel and windings involved is tight, transformer availability rather than construction speed increasingly sets the pace at which a campus can bring capacity online. For investors, the things to watch are supplier order books and backlog length, how much manufacturing capacity incumbents are adding versus how much new entrants can qualify, and whether utilities or developers begin pre-ordering transformers speculatively ahead of a firm interconnection to protect their place in the queue. Substation equipment also tends to require utility-grade qualification and testing, which limits how quickly a new supplier can be brought in even once it has capacity.