The birth of the first transformers
Between 1884 and 1885, Hungarian engineers Zipernowsky, Bláthy andDéri from the Ganz company in Budapest created the efficient "ZBD" closed-core model , which were similar to the design by Gaulard and Gibbs at first sight. (However Gaulard and Gibbs designed just an open core model). Zipernowsky, Bláthy and Déri discovered that all former (coreless or open-core) devices were incapable of regulating voltage, and were therefore impracticable. Their joint patent described a transformer with no poles and comprised two versions of it, the "closed-core transformer" and the "shell-core transformer.
In the closed-core transformer the iron core is a closed ring around which the two coils are arranged uniformly. In the shell type transformer, the copper induction cables are passed through the core. In both designs, the magnetic flux linking the primary and secondary coils travels (almost entirely) in the iron core, with no intentional path through air. The core consists of iron cables or plates. Based on this invention, it became possible to provide economical and cheap lighting for industry and households." Zipernowsky, Bláthy andDéri discovered the mathematical formula of transformers: Vs/Vp = Ns/Np. With this formula, transformers became calculable and proportionable. Their patent application made the first use of the word "transformer", a word that had been coined by Ottó Bláthy.
George Westinghouse had bought both Gaulard and Gibbs' and the "ZBD" patents in 1885. He entrustedWilliam Stanley with the building of a ZBD-type transformer for commercial use. Stanley built the core from interlocking E-shaped iron plates. This design was first used commercially in 1886.
Russian engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer in 1889. In 1891 Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for generating very high voltages at high frequency. Audio frequency transformers (at the time called repeating coils) were used by the earliest experimenters in the development of the telephone.