Research On Electronic Electrothermal Current Calculation Method For Miniature Terminal Circuit Breaker

Due to the volume constraint of miniature circuit breaker(MCB),its electronic problem has not been solved,and there are relatively few related studies.However,under the promotion of smart grid,the electronic and even intelligent MCB is imperative.Based on the project of National Natural Science Foundation of China,this dissertation studies some key problems in the electronic process of miniature terminal circuit breaker.At present,MCB has been using the "thermal magnetic" tripping mode,that is,using bimetal thermal release for overload protection and electromagnetic release for short circuit protection.In this dissertation,a "thermoelectric magnetic"(tentative name)tripping mode is proposed,and some key problems are deeply studied in order to realize the electronic MCB while keeping the original MCB volume as much as possible.This dissertation mainly studies the electrothermal current calculation method,which realizes the current calculation by measuring the temperature rise of the thermal element,and provides the current basis for the overload protection section of the electronic MCB.The main contents of this dissertation are as follows:(1)The feasibility of electrothermal current calculation method is studied.In order to verify the feasibility of this method,a kind of electrothermal system(referred to as the temperature measuring cavity)is specially designed,and the thermal circuit equation of the temperature measuring cavity is established.Through the analysis of thermal circuit,the relationship between temperature rise and current in the temperature measuring cavity is obtained.The feasibility of electrothermal current calculation method is verified through electrothermal coupling simulation and experimental research.(2)The structure of electrothermal system for electrothermal current calculation is studied.In order to use MCB as an electrothermal system,the temperature measuring cavity and MCB are compared,and the influence of two different electrothermal systems on the system model structure and model parameters is studied.It is very important to verify the equivalence of MCB's own electrothermal system and temperature measuring cavity for reducing the volume of electronic MCB.(3)Through mechanism modeling,the mathematical model of electrothermal system is established,and the functional relationship between current and stable temperature rise is deduced.A fast algorithm for measuring stable temperature rise is proposed,which is a step forward to the practical application of electrothermal current calculation method.A modified algorithm is proposed to solve the current calculation problem of electronic circuit breaker after power failure and restart(with initial temperature rise).(4)The proposed fast algorithm for stabilizing temperature rises and the modified algorithm for solving the problem of power-off and restart of electronic circuit breaker are sensitive to the model parameters.Considering the difference of model parameters of each circuit breaker in batch production,the identification method of model parameters based on recursive least square is studied.(5)The size of external conductor affects the internal temperature of circuit breaker,and then affects the accuracy of overload protection and electrothermal current calculation method.The solution is put forward.(6)An experimental platform is set up,and the experiment verifies the correctness of the proposed method.This dissertation mainly studies the electrothermal current calculation method suitable for MCB overload protection section,which can meet the needs of protection.The comprehensive error is ±10%.The electrothermal current calculation method mainly considers the demanding requirements of MCB on the volume of current sensor,and considers the isolation,measurement range and serialization.The current calculation method proposed in this dissertation provides a new idea for the current measurement of protective apparatus,and lays a foundation for the electronic MCB and miniaturization(hardware miniaturization for current calculation)of electronic circuit breaker.