Miniature Circuit Breaker Working Principle
Miniature circuit breakers are very common in commercial, industrial and residential areas. It is a converter suitable for small AC voltages. How does a miniature circuit breaker work?
Overload protection. The realization of the overload protection function of the miniature circuit breaker is based on the principle that bimetals bend in a regular direction as the temperature rises. After the miniature circuit breaker is closed, it is in normal working condition. The inner bimetal is heated by a certain current passing through it. The two pieces of metal have different thermal expansion coefficients and cause bending. The normal current (1.13 In) has a small bending angle, so the thrust is not enough to trip the tripping mechanism. When the line is generally overloaded, when the overload current (1.45 In) is reached, the bimetallic sheet has a large bending angle and touches the lever in the tripping mechanism, and the thrust is sufficient to push the tripping mechanism, so that the MCB trips and plays the role of overload protection. The magnitude of the current flowing through the miniature circuit breaker is different, and the degree of bending of the bimetal is also different. When the line is generally overloaded, because the overload current is not too large, the tripping time of the circuit breaker is generally longer.
Short-circuit protection. The short-circuit protection function of the miniature circuit breaker is realized by the instantaneous release. According to the analysis of F=IN (the suction force is proportional to the product of the current and the number of turns), due to the small number of turns of the instantaneous release coil (generally less than 10 turns), although the instantaneous release is connected in series in the circuit, when the circuit is working normally, Due to the small number of turns, the suction force generated by the normal working current is not enough to overcome the reaction force of the spring, so the line can work normally. When the line is short-circuited or severely overloaded, a very high current flows through the induction coil to generate a strong magnetic field. Since the generated current is several times or even dozens of times larger than the normal working current, the number of turns of the coil does not change, but the current increases several times or even dozens of times, so the suction force also increases several times or even dozens of times. Pushing the lever makes the circuit breaker trip quickly. Due to the large current, the tripping time of the circuit breaker is generally within 0.1s. And as long as the reaction force spring is selected reasonably, it can meet the setting requirements of B-type, C-type and D-type instantaneous release.
Another important component is the arc extinguishing grid. When the circuit breaker is closed, a large arc will be generated between the two contacts. The function of the arc extinguishing grid is to increase the heat dissipation area and the arc release space to make the arc disappear quickly and reduce the arc effects.