Seite - 44 - in Nikola Tesla and the Graz Tech

44 After a short period as a direct employee of Thomas Alva Edison in New York, Tesla founded the Tesla Electric Company with help from financial backers in 1887. Here, he continued his own research and realised his ideas. As a result, he filed a total of seven patents at the New York patent office in October 1887, and these were granted to him in May 1888. These patents described his discovery of the rotating magnetic field and, among other things, comprised an asynchronous (induction) machine, a synchronous machine, a polyphase transformer and energy transmission using polyphase alternating current /2/. In this way, a scientific basis had been created for simple conversion of elec- trical energy and for the economical transport of energy over large distances using high voltages. Tesla’s alternating current system triggered off a huge demand in the worldwide use of electricity at the end of the 19th century. His patented inventions made it possible to produce electrical energy, transport it and, above all, to convert it everywhere into mechanical power. By means of the direct-current motor developed by Antonio Pacinotti in 1860, it became possible to produce mechanical force for industrial use. The first electrical transmissions using direct-current motors were presented to the public for the first time at the world exhibitions in Vienna in 1873 and in Phil- adelphia in 1876. Thomas Alva Edison developed the first direct-current network in the USA, and the first power station to produce electricity was started up in Pearl Street, New York, in 1882. In the same year, Edison was able to establish the direct-current system as an overall concept for production, transmission and distribution in London. At that time, direct current was used in particular for electrical lighting installations /2/. Due to technical problems with the direct current network, direct-current mo- tors were only used for special machinery in large industrial companies. Com- panies involved in mass production did without this new form of actuation. As for alternating current, which emerged in these years, only electrical lighting installations were connected to the AC network since there were initially no powerful and reliable AC motors available. The Niagara Falls power station: Direct current or alternating current?