Research On Reliability Evaluation And Test Technology Of Low-Voltage Circuit Breaker

Low-voltage circuit breaker is one of the important electrical products used to transfer and distribute electric power,protect and control electric-equipments.Reliability evaluation of low-voltage circuit breaker is an important work to ensure the product quality.Generally speaking,reliability evaluation methods focus on mechanical operation and protective properties,but the influence of load stress on operation reliability of circuit breaker is not reflected.In addition,the existing reliability evaluation methods of overload protection do not take into account divergence of action time effect on the stability of product quality,and reliability test is time-consuming.Therefore,in order to comprehensively analyze and evaluate reliability of low-voltage circuit breaker,the reliability evaluation methods of electrical operation and overload protection are further studied based on failure mechanism of electrical operation and overload protection in this paper.And the solutions for problems of control technology are researched during the reliability test.Firstly,the failure distribution model of electrical operation is established by analyzing its failure mode and failure mechanism.And point estimation and interval estimation of distribution model parameters are calculated by solving the maximum likelihood estimation equations based on gray-particle swarm optimization algorithm.In addition,reliable life is taken as electrical operation reliability evaluation index and the test method of reliability evaluation is presented.Secondly,degradation failure model of electrical endurance for low-voltage circuit breaker is established according to cumulative damage theory.The model adopts contact erosion during arcing as performance degradation index and comprehensively considers the influence of load connection mode,breaking conditions and the randomness of first arc extinguishing phase.Further more,Monte-Carlo simulation method based on the above model is adopted to research the distribution model of electrical endurance under different load connection mode and contact wear limit.Then,according to test principle of the overload protection for low-voltage circuit breaker,the relational model of actuation time between rapid test current and long delay overload is established,and then range of actuation time under the rapid test current of reliability is calculated.On the basis of the distribution rule of overload protection characteristic,the variation coefficient of rapid test current actuation time is taken as the reliability evaluation index for overload protection.And the reliability sampling test plan for overload protection based on variable sampling is presented.Finally,the reliability test devices for electrical operation and overload protection are designed.In order to solve the existing problems such as large power capacity and difficult fault diagnosis in electrical operation test,alternating test control technology and multitasking test control technology are proposed.In addition,by optimizing design of software algorithms and hardware circuits of device,real-time monitoring of voltage and current and real-time computing of characteristic parameters are not only realized,and self-diagnosis and removal of test faults are accomplished as well.Also,in order to reduce period of overload protection test,series connection control method is presented and variable universe fractal fuzzy control method is used to guarantee the fast and stable regulation of test currrent.