Basic structure and working principle of miniature circuit breaker

1) handle

2) Tripping mechanism, including locks, connecting rods, trip plates

3) Contact devices, including moving and static contacts, coupling plates

4) Terminal block

5) Bimetal

6) Adjust the screw

7) Electromagnetic solenoids (also called transient coils)

8) Arc-extinguishing chamber and arc runner (Arc elimination)

9) Housing (base, cover)

2, working principle:

1) Overload protection - The overload protection function of the circuit breaker is realized by the principle that the bimetal is oriented and bent according to the temperature rise, and the miniature circuit breaker is closed under normal working condition. The internal bimetal heats up due to a certain current flowing through it. Two pieces of metal have different coefficients of thermal expansion and cause bending. The normal current (1.13In) does not have a large bending angle. Therefore, the thrust force is insufficient to trip the tripping mechanism. When the line experiences a general overload, when the overload current (1.45In) is reached, The bimetal has a large bending angle and touches the lever in the tripping mechanism, and the pushing force is enough to push the tripping mechanism, so that the tripping of the miniature circuit breaker plays a role of overload protection. The magnitude of the current flowing through the miniature circuit breaker is different, and the degree of bending produced by the bimetal is also different. In the event of a general overload of the line, the tripping time of the circuit breaker is generally longer because the overload current is not so great. In the time-current characteristics of the current GB10963.1-2005 standard, it is specified that the overcurrent trip current is 1.45 times the rated current. The trip time should be within 1 hour.

2) Short circuit protection - The short circuit protection function of the circuit breaker is realized by the instantaneous release. According to analysis of F=IN (suction force is proportional to the product of current and number of turns), since the number of turns of the instantaneous release is small (usually less than 10 turns), although the instantaneous release is connected in series in the circuit, the circuit works normally. Due to the small number of turns, the suction generated by the normal operating current is insufficient to overcome the reaction force of the spring, so the line can work normally. When the line is short-circuited or heavily overloaded, a very high current flows through the induction coil and generates a strong magnetic field. Since the generated current is several times to several tens or more times larger than the normal operating current, the number of coil turns does not change. , But the current increases several times or even tens of times, so the suction also increased several times or even tens of times, pushing the lever to quickly trip the circuit breaker, because the current is large, the tripping time of the circuit breaker is generally within 0.1s. And as long as the selection of the reaction spring is reasonable, it can meet the setting requirements of the B, C and D instantaneous release. Another important component is the arc extinguishing grid. When the circuit breaker is closed, a large arc is generated between the two contacts. The function of the arc extinguishing grid is to quickly eliminate the arc by increasing the heat dissipation area and the arc discharge space. The adverse effects.