Research On Thermomagnetic Release Capacity Of Moulded Case Circuit Breaker

Low voltage circuit breaker is the core component of low voltage distribution system,and low voltage circuit breaker’s function and performance directly affect the safety ofthe power distribution system. By analysis of the key performance of low voltage circuitbreaker, product development cycle could be shortened and costs could be reduced, aswell the core competitiveness of enterprise could be enhanced. In this paper, thethermomagnetic tripping characteristics of low voltage circuit breaker were investigated.The main research work and research results are as follows:The thermal tripping characteristics of MCCB were studied. According to theworking principle and the structure of breaker, the curvature, deflection and thrust causedby thermal elastic deformation of thermal-bimetal in thermal tripping device werededuced. The finite element model of thermal-bimetal were then established, andelectromagnetic-heat-structure coupling field analysis method was utilized to study thetemperature distribution, the displacement change, the cold-action characteristic, andother key characteristics in different working current situation of the thermal trippingdevice.The magnetic tripping characteristics of MCCB were investigated. The Maxwellmethod calculating electromagnetic force was introducted. Then, theelectromagnetic-structure coupling method of ANSYS software was adopted to analysemagnetic tripping characteristics. Firstly, the FEA model inicluding material selection,tessellation, and boundary condition was constructed. Secondly, the current distribution,electromagnetic force and torque in the current-carring conductors under short-circuitcircumstance were calculated by FEA. Finally, based on the discrete values ofelectromagnetic force and torque, a polynomial electromagnetic characteristics curve ofelectromagnetic force and torque versus work-clearance was acquired.The dynamics simulation of electromagnetic tripping device was explored. Firstly,the length and stiffness of spring in electromagnetic tripping device were optimizedbased on ADAMS software. Secondly, the electromagnetic tripping device with theoptimized key paramenters was simulated, and the curve of work-clearance, springlength, electromagnetic force, pring force, and contact force veraus time were obtained.Finally, the curves of electromagnetic torque and counter torque versus time were calculated.The experiments about thermal characteristic and magnetic characteristic weredesigned. In the thermal characteristic experiment, the change of thermal-bimetaltemperature and tripping time was measured in different current overload situation, andwas compared to the finite element analysis results. In the electromagnetic characteristicexperiment, the tripping time was also reccorded in the electromagnetic tripping device,and was compared to the dynamic simulation results. The results show that the finiteelement analysis data and dynamics simulation data have a good match with theexperimental data.