Closed-core transformer

The closed-core transformer emerged from Budapest's Ganz Works and made alternating current practical for power distribution. Three Hungarian engineers—Karoly Zipernowsky, Otto Blathy, and Miksa Deri (the ZBD team)—recognized that existing transformer designs wasted most of their magnetic energy because the magnetic field leaked into surrounding air.

The adjacent possible had assembled from Faraday's electromagnetic induction and existing open-core transformer experiments. But early transformers used linear iron cores that concentrated magnetic flux only partially. Most of the field dissipated uselessly. Efficiency hovered around 60-70%—inadequate for economical power transmission.

The ZBD insight was geometric: close the magnetic path entirely. By winding coils around a toroidal iron core, every line of magnetic flux passed through both windings. Nothing leaked. The closed core captured and redirected all magnetic energy from primary to secondary coil. Efficiency jumped to 97-98%.

Ganz Works in Budapest provided the industrial context. The company had established itself in railway and electrical equipment, accumulating expertise in precision iron work. Hungary's technical universities trained engineers in electromagnetic theory. And the Austro-Hungarian empire's ambitious electrification projects created demand for efficient power conversion.

The team presented their transformer at the 1885 Budapest National Exhibition, where it powered thousands of incandescent lamps from a single generator. The demonstration proved that AC could be transmitted at high voltage and stepped down efficiently for local use—the principle that would eventually enable continental power grids.

Westinghouse licensed the ZBD patents for American development. The subsequent War of Currents between Edison's DC and Westinghouse's AC systems was decided partly by transformer efficiency. AC won because transformers could change voltage levels easily, enabling long-distance transmission.

The closed magnetic circuit had transformed electromagnetic induction from laboratory principle to industrial workhorse. Every power grid on Earth now depends on the geometry that three Hungarian engineers worked out in Budapest.