Circuit breakers are generally composed of contact systems, arc extinguishing systems, operating mechanisms, trippers, and housings.

When a short circuit occurs, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the reaction spring, the tripper pulls the operating mechanism to operate, and the switch trips instantly. When overloaded, the current increases, the heat generation intensifies, and the bimetallic strip deforms to a certain extent to drive the mechanism to operate (the larger the current, the shorter the operation time).

There are electronic types, which use mutual inductors to collect the current size of each phase and compare it with the set value. When the current is abnormal, the microprocessor sends a signal to drive the electronic tripper to drive the operating mechanism to operate.

The function of the circuit breaker is to cut off and connect the load circuit, as well as to cut off the fault circuit, prevent the accident from expanding, and ensure safe operation. The high-voltage circuit breaker must break the arc of 1500V and the current of 1500-2000A. These arcs can be stretched to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved for high-voltage circuit breakers.

The principle of arc blowing and arc extinguishing is mainly to cool the arc and weaken the thermal ionization. On the other hand, the arc is stretched by blowing to strengthen the recombination and diffusion of charged particles, and the charged particles in the arc gap are blown away at the same time, quickly restoring the dielectric strength of the medium.

Low-voltage circuit breakers are also called automatic air switches. They can be used to connect and disconnect load circuits, and can also be used to control motors that are not frequently started. Its function is equivalent to the sum of some or all functions of electrical appliances such as knife switches, overcurrent relays, undervoltage relays, thermal relays and leakage protectors. It is an important protective electrical appliance in low-voltage distribution networks.

Low-voltage circuit breakers have multiple protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action values, high breaking capacity, easy operation, safety and other advantages, so they are widely used. Structure and working principle Low-voltage circuit breakers are composed of operating mechanisms, contacts, protection devices (various trippers), arc extinguishing systems, etc.