Air switch is also called vacuum circuit breaker. There are many kinds of circuit breakers, which can be divided according to the number of poles, protection form, full section time and structural type. Circuit breaker is a very important electrical appliance in low-voltage distribution network and electric drive system. It integrates control and multiple protection functions. In addition to completing the contact and breaking of the circuit, it can protect the short circuit, serious overload and undervoltage of the circuit or electrical equipment. At the same time, it can also be used to start the motor infrequently. Its main function is to automatically trip when the specified load current is exceeded to protect the main line and electrical appliances.

Rated current means that the circuit breaker can work for a long time under this current. In other words, when selecting the circuit breaker, the sum of the load current should be less than or equal to the rated current of the circuit breaker. When the load current exceeds this current, the circuit breaker will act, and the action time has an inverse time limit. For the specific action time, you can check the action curve of the circuit breaker. Check according to the multiple of the load current exceeding the rated current of the circuit breaker. For example, when it is 1.2 times, the circuit breaker will open after several seconds. From this point of view, the circuit breaker has certain overload protection capacity, because the circuit breaker is designed for short-circuit protection.

General circuit breakers can be divided into type C and type D. type C is used for power distribution and type D is used for power. For example, the motor should choose type D. In order to avoid the misoperation of the circuit breaker when the motor is started, the circuit breaker shall choose a higher model when controlling the motor. For example, the current of 7.5kW motor is about 15a, and the circuit breaker should be 20a-25a. For some devices, such as frequency converter and switching power supply, at the moment of power on, due to the internal capacitance, the instantaneous current is relatively large. Therefore, when selecting the circuit breaker, we must pay attention to it, rather than simply according to the current after stable operation.

The above is only the current selection principle to ensure the normal start-up and operation of the circuit breaker, but the circuit breaker is a protective device, its function is short-circuit protection, and the most important parameter of short-circuit protection is the breaking capacity of short-circuit current. If a short-circuit accident occurs, the circuit breaker also acts instantly, but because the breaking capacity of the circuit breaker is less than the short-circuit current, the arc cannot be extinguished.

Therefore, when selecting the circuit breaker, the expected short-circuit current should be calculated. Ensure that the breaking capacity of the circuit breaker is greater than the expected short-circuit current.

The circuit breaker involves many things: such as how to break the DC, how to achieve the selectivity (not beyond the level), and so on. There are many types of circuit breakers. There are also slight differences in the functions of circuit breakers in different countries. It is suggested to see more relevant samples.

About the name of air switch and circuit breaker, air switch is the common name of air circuit breaker, which is generally used for low voltage. The name is related to arc extinguishing medium. There are vacuum and oil circuit breakers, which are used for high voltage. The formal name of general air switch is circuit breaker.