These circuit breakers used sulfur hexafluoride (chemical formula: SF 6) as the arc quenching medium. The modular system used in all Siemens SF 6 circuit breakers ensured very reliable operation and easy maintenance. Ten years later, the Siemens puffer circuit breaker brought the second generation of SF 6 circuit breakers onto the market. In 1964, Siemens was the first company in Europe to introduce a 220 kV SF 6 high-voltage circuit breaker. Vacuum circuit breakers became established for the medium-voltage range (1 to 50 kilovolts, kV), while SF 6 high-voltage circuit breakers came in for applications above 72 kV. After that point, “minimum oil” circuit breakers started giving way to other forms. It became a foundation for the interconnection of various grids to create an interregional power supply.īy World War II, the "expansion" circuit breaker, using steam (or later, oil) as an arc quenching medium, had been developed for switching high voltages.
The expansion circuit breaker opened a new chapter in high-voltage circuit breaker construction. Siemens was the first company to develop an oil-free circuit breaker that used water as an arc quenching medium. This caused high pressure to develop, which would cool or extinguish the arc if the flow was designed right. In this "expansion circuit breaker," the arc that occurred during switching evaporated some of the surrounding water. In 1930, Siemens introduced a fluid circuit breaker that used water as the arc quenching medium. So electric utility companies were looking for oil-free switches. But this kind of circuit breaker was vulnerable to occasional horrific explosions, because a gas mixture could form between the surface of the oil and the cover, and could ignite when incandescent gas rose during switching.
The first solution to become established was the oil circuit breaker, which has its contacts inside an oil-filled chamber. The continuous rise in power grid voltage in the 1920s also increased demands on switching equipment. The cable was a milestone in the history of German cable technology, and made it possible to connect long-distance transmission lines safely with urban centers. As the next layer, the cable was wrapped in a thick lead sheath, which in turn was covered with a sheath of asphalt and fiber material to protect it from chemical reactions and stray currents. At the same time, the hollow-core conductor collected the surplus oil that developed as the cable heated up during operation, and channeled it to compensation reservoirs. It was surrounded with a layer of paper insulation, which was impregnated with transformer oil conveyed via the hollow-core conductor. The heart of the cable was the hollow-core conductor. That same year the company began developing a 110 kV oil-filled cable, and within only about two years, the company had built a reliable version that was far superior to the former mass-filled design. In 1923, Siemens had already built the first 60 kilovolt (kV) triplex cable with conventional technology, and in 1925 it delivered a 100 kV cable with mass filler to Braunschweig Technical University in Germany.
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