Seite - 53 - in Nikola Tesla and the Graz Tech

53 The War of the Currents of many years, which had split American industry into two camps, ended with the award of the contract to the Westinghouse Com- pany and the recognition of the polyphase alternating current system. The victory in the War of the Currents led the Westinghouse Company to becom- ing a global enterprise which at the time employed 50,000 people. Soon afterwards, alternating current was supplied to the Pittsburgh Reduc- tion Company, which later became the Aluminium Company of America. The metal processing industry and especially the aluminium industry had waited for the necessary high voltages, which could only be supplied by alternating current, in order to be able to use fused-salt electrolysis. Aluminium was used in ship construction as well as in the manufacture of bicycle frames, zeppe- lins, construction facades, overhead power lines, lightning conductors and ta- bleware. Aluminium production enabled rapid progress in the aircraft industry between the two world wars /3/. Tesla’s polyphase alternating current system prevailed due to its technical and physical advantages and is even today the most relevant public electricity supply system. The standardisation of the alternating-current frequency also served as a unified power system. Around 1900, electrical industrial compa- nies in the USA agreed a frequency of 25 Hz for electrical transport and large motors, and 60 Hz for the normal consumer network. In Europe the public electricity network settled on a frequency of 50 Hz. Today, only the frequen- cies of 50 Hz and 60 Hz are encountered in public electricity networks. Special applications use diverging frequencies, e.g. 16.7 Hz in railway technology and 400 Hz in the aerospace industry. It should be mentioned that with the development of mercury-arc rectifiers (from 1940) and powerful semiconductor components such as thyristors and IGBTs today, the economical transmission of electrical energy in the form of high-voltage direct current transmission routes of up to ±800 kV can be im- plemented. With the help of the described technology, electrical energy can be exchanged between networks of differing alternating current frequencies at high efficiency. The technologies which were earlier opposed to each other in the War of the Currents supplement each other today to create a powerful and economical electricity grid.