Reliability Analysis And Evaluation Of Operating Mechanism In Miniature Circuit Breaker

Miniature circuit breaker is mainly used for overload and short circuit protection ofelectrical lines and equipment for household and similar places,and plays a crucial role in thelow voltage distribution network. Operating mechanism as a key component of the overloadand short circuit function in miniature circuit breaker, plays a decisive role in the reliability ofminiature circuit breaker. In this dissertation, takes the widely used DZ47-60type of miniaturecircuit breaker is as the research object,and the reliability analysis of the operating mechanismof miniature circuit breaker has been deeply researched.Firstly, we briefly summarize the reliability engineering developing history and currentsituation, sketch current situation and existing problem of reliability research of the miniaturecircuit breaker,and mechanism reliability’s main contents, methods, current situation anddeveloping trends at home and abroad. This paved the way for the research on reliabilityanalysis for operating mechanism of miniature circuit breaker.Second, analysed the operating characteristics and requirements of the miniature circuitbreaker. Due to the test and filed data, FMECA of the miniature circuit breaker was made inorder to get the main failure modes. On this basis, the main failure modes as top event, the mainfailure reasons of the miniature circuit breaker were found by FTA.Third, using the method of electrical thermal structural coupled with the finite elementsoftware Ansys,and analyzed the release process of thermal release (thermostatic bimetal-strip).Temperature distribution and displacement curve of thermostatic bimetal-strip at differentcurrent excitation was obtained. For miniature circuit breakers in a current overload occursunder the release as an example, calculated the release force at its time, and laid a foundationfor the motion reliability analysis of the operating mechanism.Fourth, by using the method of static force analysis, the closing force and closing moment,the force between each components and the torsion spring torque were analyzed. According tothe kinematic and dynamic principle, the operating mechanism model were established. Usingmulti-body dynamics software Adams for analyzing kinetic analysis of the miniature circuitbreaker operating mechanism at overload release time, and studied on effect of moving contactspeed and displacement on dynamic performance of operating mechanism. This can obtain when the contacts attachment torsion stiffness become greater and the moment inertia of thecontacts attachment become smaller, the speed of the moving contacts will be faster, that thebreaking time of miniature circuit breakers will be shorter.Fifth, by building reliability model of the miniature circuit breaker operating mechanismwhen released during initiating stage, get the reliability and sensitivity of each componentparameters of the operating mechanism by using the Monte Carlo method at breaking time,proposed by changing the material properties of the release lever torsion and the force arm ofeach force to increase the operating mechanism action reliability. According to the complexprocess of the reliability and sensitivity when solving of the operating mechanism at motionstage, proposed method that use of kriging model to replace the limit state equation to solveexercise phase the reliability and sensitivity of operating mechanism at motion stage, proposedby changing the parameters of operating mechanism each component to increase the operatingmechanism kinematics accuracy reliability.