A circuit breaker refers to a switching device that can close, carry and break current under normal circuit conditions and can close, carry and break current under abnormal circuit conditions within a specified time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their scope of use. Circuit breakers can be used to distribute electric energy, start asynchronous motors infrequently, and protect power lines and motors. When they have serious overload or short-circuit and under-voltage faults, they can automatically cut off the circuit. Its function is equivalent to a fuse switch. Combination with overheating and underheating relay, etc. Moreover, it is generally not necessary to change the components after breaking the fault current. They have been widely used in different fields. The world's earliest circuit breaker was produced in 1885, which is a combination of a knife head and an overcurrent release. In 1905, the air circuit breaker with free tripping device was born. Since 1930, with the advancement of science and technology, the discovery of the arc principle and the invention of various arc extinguishing devices have gradually formed mechanisms. In the late 1950s, due to the rise of electronic components, electronic trip units were produced. Today, due to the popularization of single-chip microcomputers, intelligent circuit breakers have appeared.