Seite - 54 - in Nikola Tesla and the Graz Tech

54 High frequency, the Tesla transformer and the Wardenclyffe Tower Fig.: Tesla transformer at the Institute of High Voltage Engineering and System Performance at Graz University of Technology (Photo/montage: Kniepeiss). In addition to the development of the polyphase alternating-current system, in 1889 Tesla turned his attention to high frequency electricity and its effects. At the beginning, this was only meant to provide an improved lighting system using arc lamps. In a number of experiments, based on James Clerk Maxwell and Heinrich Hertz’s work on electromagnetic waves, he developed high-frequency alternators with frequencies of up to 30,000 Hz /3/. His research culminated in the construction of a working ‘resonant transformer’ based on the resonance principle, which also came to be known as the Tesla transformer or Tesla coil. This device basically consisted of a spirally shaped primary and secondary winding with air at its core, a capacitor and a spark gap. In a different circuit configuration, instead of the spark gap, a high-frequency alternator is used. By means of the resonance oscillating circuit, Tesla was able to produce very high high-frequency voltages at low current strength. Tesla managed to produce voltages up to four million volts and artificial lightning five metres long in his laboratory using a Tesla coil. In later years the resonant transformer became a basis for Tesla’s idea of a wireless energy transmission over long distances.