Modern Period
Voltages used for electric power transmission increased throughout the 20th century. The first electric power transmission line in North America operated at 4000V. It went online on June 3, 1889, with the lines between the generating station at Willamette Falls in Oregon City, Oregon, and Chapman Square in downtown Portland, Oregon stretching about 13 miles. By 1914 fifty-five transmission systems operating at more than 70,000 V were in service, and the highest voltage then used was 150,000 volts. The first three-phase alternating current power transmission at 110 kV took place in 1907 between Croton and Grand Rapids, Michigan. Voltages of 100 kV and more were not established technology until around 5 years later, with for example the first 110 kV line in Europe between Lauchhammer and Riesa, Germany in 1912.
In the early 1920s the Pit River – Cottonwood – Vaca-Dixon line was built for 220 kV transporting power from hydroelectric plants in the Sierra Nevada to the San Francisco Bay Area, at the same time the Big Creek - Los Angeles lines where upgraded to the same voltage. Both of those systems entered commercial service in 1923. On April 17, 1929 the first 220 kV line in Germany was completed, running from Brauweiler near Cologne, over Kelsterbach near Frankfurt, Rheinau near Mannheim, Ludwigsburg–Hoheneck near Austria. This line comprises the North-South interconnect, at the time one of the world's largest power systems. The masts of this line were designed for eventual upgrade to 380 kV. However the first transmission at 380 kV in Germany was on October 5, 1957 between the substations in Rommerskirchen and Ludwigsburg–Hoheneck.
The world's first 380 kV power line was built in Sweden, the 952 km Harsprånget - Hallsberg line in 1952. In 1965, the first extra-high-voltage transmission at 735 kV took place on a Hydro-Québec transmission line. In 1982 the first transmission at 1200 kV was in the Soviet Union.
The rapid industrialization in the 20th century made electrical transmission lines and grids a critical part of the economic infrastructure in most industrialized nations. Interconnection of local generation plants and small distribution networks was greatly spurred by the requirements of World War I, where large electrical generating plants were built by governments to provide power to munitions factories; later these plants were connected to supply civil load through long-distance transmission.
Small municipal electrical utilities did not necessarily desire to reduce the cost of each unit of electricity sold; to some extent, especially during the period 1880–1890, electrical lighting was considered a luxury product and electric power was not substituted for steam power. Engineers such as Samuel Insull in the United States and Sebastian Z. De Ferranti in the United Kingdom were instrumental in overcoming technical, economic, regulatory and political difficulties in development of long-distance electric power transmission. By introduction of electric power transmission networks, in the city of London the cost of a kilowatt-hour was reduced to one-third in a ten-year period.
In 1926 electrical networks in the United Kingdom began to be interconnected in the National Grid, initially operating at 132,000 volts.
Read more about this topic: History Of Electric Power Transmission
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