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The basic structure and working principle of Miniature circuit breaker

1, composed of:

1) handle

2) tripping agencies, including the lock, connecting rod, trip plate

3) Contact device, including moving contact, connecting plate

4) terminal block

5) bimetal

6) Adjust the screw

7) electromagnetic solenoid (also known as instantaneous coil)

8) interrupter and arc plate (arc suppression device)

9) Shell(base, cover)

2, the working principle:

1) Overload protection – The overload protection function of the Miniature circuit breaker is to use the principle that the bimetal will be bent according to the law as the temperature rises. After the Miniature circuit breaker is closed, it will work under the normal working condition. The internal bimetal heats up by a certain amount of current on it. Due to the different thermal expansion coefficient of the two metals, the normal bending current (1.13In) is not large, so the thrust is not enough to trip the tripping mechanism. When the overcurrent is overloaded, the overcurrent (1.45In) Bimetal bending angle larger and touch the lever in the tripping mechanism, the thrust enough to promote the tripping mechanism, so that the tripping of the Miniature circuit breaker has played the role of overload protection. The current flowing through the miniature circuit breakers varies in size, and the degree of bending produced by the bimetallic strip is also different. In the general line overload, due to overload current is not too large, circuit breaker tripping time is generally longer. In the current GB10963.1-2005 standard time-current characteristics of the overcurrent tripping current is 1.45 times the rated current. Tripping time should be within 1 hour.

 

2) Short Circuit Protection – The short circuit protection of the Miniature circuit breaker is achieved by the instantaneous trip unit. According to F = IN (suction and current proportional to the product of the number of turns) analysis, due to instantaneous release coil turns less (usually only 10 turns below), although the instantaneous release in series in the circuit, the circuit is working , Due to the small number of turns, the normal operating current generated by the suction enough to overcome the spring reaction, so the circuit can work properly. When a line is short-circuited or severely overloaded, a very high current flows through the induction coil and a strong magnetic field is generated. Since the generated current is several times or even several tens of times larger than the normal operating current, the number of turns of the coil does not change , But the current increase several times or even several times, so the suction also increased several times or even tens of times, to promote the lever to trip the circuit breaker quickly, due to the current, circuit breaker trip time is generally within 0.1s. And as long as the reaction force selection of reasonable, can meet the B-type, C-type, D-type instantaneous release setting requirements. There is still one important part 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 quickly eliminate the arc by increasing the heat dissipation area and arc release space, so as to reduce arc-generated defects influences.

Miniature circuit breaker2
miniature circuit breaker1