교류
Alternating current had been under development with contributions by Guillaume Duchenne (1850s), the dynamo work of Zénobe Gramme, Ganz Works (1870s), Sebastian Ziani de Ferranti (1880s), Lucien Gaulard, and Galileo Ferraris. Starting in the 1880s alternating current gained its key advantage over direct current with the development of functional transformers that allowed the voltage to be "stepped up" to much higher transmission voltages and then dropped down to a lower end user voltage for business and residential use. The high voltages allowed a central generating station to supply a large area, up to long circuits.