Study On The Promotion Of MCCB’s Interruption Capability Based On Improve Arc Extinguishing System

MCCB(Moulded Case Circuit Breaker)is a mechanical switching device which is not only can connect、carry and interrupt the normal current but also can connect,load current at a certain period of time and interrupt the fault current under the non-prescribed conditions(such as overload or short circuit).It is used widely in low voltage distribution system as one of the important distribution device.With the development of modern industry,the power industry is further developed also,the maximum short-circuit current value has become more and more expected line;once the MCCB can’t be reliably interrupt will cause contacts are welded、explosion etc.accidents and what is more serious is that even threaten the safety of electrical operators.Therefore,it is necessary to improve the interrupting capacity of MCCB,then can improve its ability to cut off the fault current unceasingly.This topic is according to the marketing’s demand to improve the interrupting capacity which based on the original 50kA,in order to improve to 70kA,thearc extinguishing system of MCCB was optimized.Based on the study of the theory of arc interrupt process which included electric repulsion、arc magnetic force and arc voltage etc.From the following four items to research(1)The influence of the shape of different fix contact bars on the repulsion moment of the moving contact bar when interrupt the fault current;(2)The influence of the magnetic blow force when the arc entered the arc chamber which included with the magnetic blow plates or not、the shape of the magnetic blow plates and the position in the arc chamber system;(3)The influence of arc extinguishing plates to arc voltage which included extinguishing plates’ numbers、shape and arrangement in the arc chamber;(4)The influence of the structure of air blowing plate and the material of the blowing film to the arc voltage;through these studies a variety of design proposals were proposed and also used ANSYS&Fluent simulation software to calculation and comparison at the meantime.According to the comparison of simulation results over different schemes,fixed the preliminary optimal design proposal and made the prototype sample to do limit operation short circuit interrupting test at 25 degree under the condition of 415 V AC voltage and the power factor is 0.2,used Teamplus software to grab test waveform during the test,calculated the peak current&the arc’s energy and spread the analysis and research about the interrupting test and follow-up validation tests such as electrical life,dielectric test,characteristics and temperature rise,found the corresponding solutions one by one then optimized the design scheme further.The researching achievement gets an optimized design of arc extinguishing system:improved optimization of arc extinguishing plates’ arrangement in arc chamber and combine with slot motor magnetic blow structure and gas blowing plates,the new component overcomes the problems encountered during the previous experiment,finally the MCCB which use the improved arc extinguishing system pass all tests successfully,achieve the product’s interrupting capacity increase from 50kA to 70kA.The researching achievement has a certain significance for the follow-up new development and design improvement of MCCB arc extinguishing system.