Moulded case circuit breaker (MCB) is mainly composed of operating mechanism, contact system, arc extinguishing system and support. The operating mechanism is the main mechanical part of MCB to execute the on and off action command, which provides energy for reliable on / off of MCB. Therefore, the mechanical characteristics of MCB mainly depend on the operation Through studying the mechanical characteristics of the operating mechanism, we can have a comprehensive understanding of the operating mechanism of MCCB.

1 Mechanical Characteristics of MCCB

1.1 opening distance

Open distance refers to the distance between the moving contact and the static contact of the circuit breaker from the opening state. The opening distance is a kind of electrical gap, through which the voltage breakdown between the moving and static contacts will not occur when the circuit breaker is disconnected.

1.2 final contact pressure

Under the action of the main spring tension, the moving contact will close with the static contact and produce a closing force, which is called the final pressure. The final pressure is the main mechanical characteristic parameter to ensure the contact stability and temperature rise of the circuit breaker, as well as the important parameter of ICU / ICs size. Increasing the final pressure can reduce the contact resistance and reduce the temperature rise of the circuit breaker. At the same time, excessive increase of the final pressure can also cause abnormal bounce when the contact is closed. At present, the more advanced method is to carry out virtual simulation analysis and calculation on the contact terminal pressure during the design and development through three-dimensional modeling, and then carry out routine quality measurement and control on the mechanical characteristic parameters in the production process manufacturing, so as to ensure that the product has higher stability and reliability.

1.3 overtravel

Overtravel is the distance needed to rotate when the circuit breaker is in the closed state and the moving contact is closed from the static contact to the separation process. Overtravel is also called contact stroke. The main function of overtravel is to ensure the reliable contact between the moving and static contacts, provide the service life of the circuit breaker and avoid accidents, although the contacts are reduced due to wear or burning after several times of normal current switching or fault current breaking.

1.4 mechanical life

According to the standard GB / T 14048, it should be called operation performance, times, and mechanical life in the industry. In actual use, the molded case circuit breaker (miniature circuit breaker) is not frequently switched on and off, so the requirement of mechanical life in GB / T 14048 standard is not high. The mechanical life of circuit breaker in China is low, so enterprises need to improve the mechanical life of products.

1.5 closing time

When the circuit breaker is in the opening position, the time interval from the start of closing to the contact between the moving contact and the static contact of all poles.

1.6 opening time

When the circuit breaker is in the closing position, the time interval from the moment when the product release is powered on to the moment when all moving contacts and static contacts are separated and all pole arcs are finally extinguished. The opening time of circuit breaker includes inherent opening time and arc extinguishing time. The inherent opening time refers to the time from the action of the release system of the operating mechanism to the contact separation, and the arc extinguishing time refers to the time from the contact separation to the arc extinction of each phase. Both are called full opening time. Now the more advanced method is to establish the opening time parameters in the virtual simulation software through three-dimensional virtual simulation modeling. In the virtual simulation system, the inherent opening time of the operating mechanism is shortened by optimizing the design of the connecting rod structure of the circuit breaker operating mechanism. Then, the optimized operating mechanism prototype is printed and manufactured by using 3D printing technology, and then the experimental prototype is available Finally, the opening time of the circuit breaker is shortened.