Nikola Tesla's AC Motor
In 1888, the Serbian-born inventor Nikola Tesla received U.S. patents for a polyphase alternating current (AC) induction motor and a system of power transmission built around it. The motor solved a practical problem that had held back AC electricity: until then, there was no reliable way to turn alternating current into mechanical work. With it, AC could power factories and streetcars as well as lamps, and it became central to the electrical grids that still supply the modern world.
Tesla was born in 1856 in what is now Croatia, then part of the Austrian Empire, and studied engineering in Graz before working in Budapest and Paris. He had become interested in the idea of a motor driven by a rotating magnetic field, which would avoid the sparking commutators and brushes that wore out direct current (DC) machines. He emigrated to the United States in 1884 and briefly worked for Thomas Edison's company, then left within a year or so. Edison's firm had built its fortune on low-voltage DC systems, which could serve customers only within a mile or so of a power station.
Tesla's approach used two or more alternating currents, offset in timing, to create a magnetic field that rotated within the motor and dragged a rotor along with it. The design was simple, sturdy and efficient. Similar ideas were being pursued elsewhere, and the Italian physicist Galileo Ferraris demonstrated a rotating-field motor in 1885 and published his work in 1888. Historians generally credit both men with independent contributions, though Tesla's patents proved the more commercially influential. Tesla presented his work to the American Institute of Electrical Engineers in 1888.
The patents attracted the industrialist George Westinghouse, who was already promoting AC distribution and bought the rights to Tesla's designs. AC's great advantage was that transformers could raise its voltage for efficient long-distance transmission and lower it again for safe use. The rivalry that followed with Edison's DC interests is often called the "War of Currents." It included public relations campaigns, notably Edison-aligned claims about AC's dangers, and fierce competition for contracts.
AC prevailed over the following decade. The Westinghouse company lit the 1893 World's Columbian Exposition in Chicago, and in 1895–96 a hydroelectric plant at Niagara Falls began sending AC power to Buffalo, using Westinghouse generators based on Tesla-era polyphase principles. Edison's company later merged into General Electric, which itself adopted AC.
Tesla's later life was marked by brilliant experiments and financial troubles, but the induction motor remained his most lasting achievement. Descendants of his design still drive pumps, fans, appliances and industrial machinery worldwide, and the unit of magnetic flux density, the tesla, bears his name.