The circuit breaker can close, carry and break the current under normal circuit conditions, and can close, carry and break the current under abnormal circuit conditions (including short circuit conditions) within the specified time. The circuit breaker can be used to distribute electric energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off the circuit in case of serious overload, short circuit, undervoltage and other faults. Its function is equivalent to the combination of fuse switch and over/under heating relay. In addition, it is generally unnecessary to change parts after breaking the fault current. At present, it has been widely used. When entering the new century, China's low-voltage electrical appliances (low-voltage circuit breakers) will develop in accordance with the requirements of "miniaturization, high breaking, low noise, reliable operation, and gradually realizing intelligence", and constantly create new products that meet the needs of the times.

The development of circuit breakers is still dominated by intelligent ones, and their intelligent functions are further improved on the basis of DW45. In terms of communication functions, they will be attached to the EC communication interface (protocol) with larger capacity and faster speed on the basis of the connection between the current intelligent controller and the RS485 interface protocol (Profibus system), so as to achieve more comprehensive remote control, telemetry, teleconference and telecontrol of small, medium and large area field buses.

The circuit breaker is generally composed of contact system, arc extinguishing system, operating mechanism, release, shell, etc. With the increase of power grid, the short circuit breaking capacity of the circuit breaker as the protection switch at the low-voltage side of the transformer will be increased to 120~150kA, and its volume will also be reduced. The accessories of the circuit breaker shall be modular and modular.

Circuit breakers are divided into high voltage circuit breakers and low voltage circuit breakers according to their scope of use. The high and low voltage boundaries are relatively vague, and those above 3kV are generally referred to as high-voltage electrical appliances. Low voltage circuit breaker, also known as automatic switch, commonly known as "air switch", also refers to low-voltage circuit breaker. It is an electrical appliance that can not only switch manually, but also automatically protect against voltage loss, undervoltage, overload and short circuit. It 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, undervoltage and other faults, it can automatically cut off the circuit. Its function is equivalent to the combination of fuse switch and over/under heat relay. In addition, it is generally unnecessary to change parts after breaking fault current, which has been widely used. Industrial automation, equipment, machines, machine tools, etc. are all applied. It can also be used in daily life, such as lighting. There are circuit breakers in the switch box of the family.

High voltage circuit breaker (or high-voltage switch) is the main power control equipment in power plants and substations, with arc extinguishing characteristics. When the system operates normally, it can cut off and connect the no-load and load current of lines and various electrical equipment; When the system fails, it can cut off the fault current as soon as possible with the cooperation of relay protection to prevent expanding the scope of the accident. Therefore, the work of high-voltage circuit breaker directly affects the safe operation of power system; There are many types of high-voltage circuit breakers, which can be divided into oil circuit breakers (more oil circuit breakers, less oil circuit breakers), sulfur hexafluoride circuit breakers (SF6 circuit breakers), vacuum circuit breakers, compressed air circuit breakers, etc.