The earliest electrical appliances were knife switches used by 18th century physicists to study electrical and magnetic phenomena. In the late 19th century, due to the application of electric energy to the society, various electrical appliances were also introduced. However, the electrical capacity of this period is small and it is manual. The protection of the circuit mainly uses fuses (commonly known as fuses). Since the 20th century, the application of electric energy has shown great superiority in social production and human life, and it has rapidly spread, and electrical appliances that adapt to various requirements have also emerged. Large ones have two or three-story ultra-high voltage circuit breakers used in power systems, and small ones have ordinary household switches.
In the past 100 years, the general trend of electrical development has been an increase in capacity, an increase in transmission voltage, and an increase in automation. For example, switching electrical appliances used air or transformer oil as an arc extinguishing medium in the early 20th century. After multi-oil, oil-less, and compressed air, they developed into an open circuit using vacuum as an arc extinguishing medium and sulfur hexafluoride as an arc extinguishing medium. The breaking capacity of the device is from about 20 to 30 kiloamperes in the early period to 80 to 100 kiloamperes in the middle and late 1980s, and the working voltage is increased to 765 kilovolts to 1150 kilovolts.
For example, in the 1960s, transistor time relays, proximity switches, and thyristor switches appeared. After the 1970s, there were electromechanical integrated intelligent appliances and sulfur hexafluoride fully enclosed combined electrical appliances. The emergence of these electrical appliances is interdependent and mutually reinforcing with new electrical materials, new electrical manufacturing technologies and new processes, and has adapted to the requirements of the continuous development of the entire power industry and social electrification.
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