Circuit breakers are generally composed of contact system, arc extinguishing system, operating mechanism, trip unit, shell and so on.
When a short circuit occurs, the magnetic field generated by the large current (usually 10 to 12 times) overcomes the reaction force spring, the trip unit pulls the operating mechanism, and the switch instantly trips. When overloaded, the current becomes larger, the heat increases, and the bimetal deforms to a certain extent to push the mechanical device to move (the larger the current, the shorter the action time).
There is an electronic type that uses a transformer to collect the current of each phase and compare it with a set value. When the current is abnormal, the microprocessor sends a signal to make the electronic trip unit drive the operating mechanism.
The function of the circuit breaker is to cut off and connect the load circuit, as well as to cut off the faulty circuit, to prevent the expansion of the accident and ensure safe operation. The high-voltage circuit breaker needs to disconnect the 1500V, current 1500-2000A arc, these arcs can extend to 2m, and continue to burn without being extinguished. Therefore, arc extinguishing is a problem that must be solved by high-voltage circuit breakers.
The principle of arc blowing and arc extinguishing is mainly to cool the arc to reduce thermal decomposition. On the other hand, the arc is stretched by the arc to enhance the recombination and diffusion of charged particles, and at the same time, the charged particles in the arc gap are blown away to quickly restore the dielectric strength of the medium.
Low-voltage circuit breakers are also called automatic air switches, which can be used to connect and disconnect load circuits, and can also be used to control motors that start infrequently. Its function is equivalent to the sum of part or all of the functions of a knife switch, an overcurrent relay, a voltage loss relay, a thermal relay and a leakage protector. It is an important protective electrical appliance in the low-voltage distribution network.
Low-voltage circuit breakers have a variety of protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action value, high breaking capacity, convenient operation, high safety, etc., so they have been widely used. Structure and working principle The low-voltage circuit breaker is composed of operating mechanism, contacts, protection devices (various releases), arc extinguishing system, etc.
The main contacts of low-voltage circuit breakers are manually operated or electrically closed. After the main contact is closed, the free trip mechanism locks the main contact in the closed position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the power supply. When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release will be pulled in, causing the free trip device to work and the main contact to disconnect the main circuit. When the circuit is overloaded, the heating element of the thermal trip unit will bend the bimetal and push the free trip mechanism to move. When the circuit is undervoltage, the armature of the undervoltage release is released. This also makes the free travel mechanism work. The shunt release is used for remote control. During normal operation, its coil is cut off. When distance control is required, press the start button to energize the coil.