In the early years of using electrical energy, direct current DC generators were connected to the same voltage at the same voltage as the electricity generation and transmission with a voltage, because there was no way to change the DC voltage except for the change of generators.
Since the inflammatory bulbs of that time were only available at a voltage of 100 V, the only possible way was to generate electricity with this voltage. Also, low voltages did not require much insulation to maintain safety, and thus the production and transmission of 100 volts was carried out, resulting in significant losses along the lines.
From the very beginning, the use of copper as a conductor was very common, due to the relative electrical conductivity and relatively good copper price (today, with the cost of copper rising from the cost of this metal), compared to other metals. To reduce flow and therefore reduce copper consumption, higher voltages should be used along the lines. But as mentioned, there was no method available to change the DC voltage existing at that time, so the Edison DC system needed thick cables and local generators. The distance between the last consumer and the maximum should be 1.5 miles from the place of manufacture, so there is no need to use conductors with a very high cross-section.
Acceptance of the alternating current AC was accompanied by fundamental changes in the field of electricity, because the electrical transformers could change the voltage and this would allow for an increase in the length of the transmission lines. With the increase in voltage across the lines, the electric current was reduced, thus requiring the use of high-cross-section cables and local generators, which would also allow electric power to be produced at distant consumers.
Using larger multipliers that were connected to a large area, the cost of finished electricity was reduced, allowing for the use of higher-efficiency power plants that could feed different loads. In this way, the stability of electricity generation increased, and the cost of investment in this sector decreased, and eventually the use of remote energy sources such as hydroelectric power plants or coal mines, without the need to pay for the transportation of fuels Was provided.
In the primary transmission lines, pin-and-sleeve insulators were used. These insulators look like insulators used today for airline lines. The use of these insulators was limited because they could be used up to 40 kV. In 1907, the invention of plate insulators by Harold W. Buck of Niagara Falls Power provided the possibility of using insulators at higher voltages, so that the first transmission line for high electrical energy in the United States between the power plant The hydroelectric power of the Niagara Falls and Buffalo were created in New York. Nicola Tesla's statue is now grateful for her contribution to electricity transmission along the Niagara Falls.
During the twentieth century, the transmission voltage increased gradually. In 1914, fifty five transmission lines with a voltage of more than 70 kilovolt were used, with the highest transmission voltage of 150 kV. The first three-phase transmission line was also launched in 1912 with a voltage of 110 kilos in Germany between the Lockheater and Reza. On April 17, 1929, the first 220 kilovolt transmission line was launched in Germany, which crossed the proximity of four cities on its route. In this line, the towers were made to increase the potential to 380 kV. The first 380 kV transmission line was built in 1957, ten years later, in 1967, the first transmission line with a high voltage of 735 kV was constructed. Eventually, in 1982, a Soviet-Iranian transmission line was constructed with a voltage of 1200 kV; this voltage is the highest voltage used in transmission lines in the world. The reason for the use of such a voltage in the Soviet Union was that it was widespread in comparison with urban densities.
The acceleration of industrialization in the twentieth century quickly turned electric energy into one of the most important infrastructure in industrialized countries. Thus, local generators and small distribution networks quickly replaced their energy production and transmission networks. With the onset of World War I, the acceleration of these changes has been added and governments have quickly begun to build large power plants to produce electrical energy needed by gunsmiths. Later these plants were used to feed urban consumers.