Transient Process Analysis Of Overload Current Fault Of 12kV High Voltage Expulsion Fuse

High voltage expulsion fuse is the main protection equipment of outdoor transformer.In order to protect the transformer and other electrical equipment from overload current,it is necessary to study the transient process of the overload current of the expulsion fuse.The physical process of the transient process of the overload current of the fuse is complicated.In order to facilitate the study and combine the actual process of the breaking physical process,the transient process of breaking the overload current is divided into pre-arcing process and arc process in this paper.The research work is carried out in the following three aspects.Firstly,combined with the equivalent circuit of fuse,the paper analyzed the mathematical model of temperature field and electric field under the overload current fault of the pre-arcing process.By using the finite element analysis software COMSOL Multiphysics,the temperature field and electric field of A type fuse and B type fuse are simulated when the overload current is 19 A and the rated currents of the two fuses are 6A.The temperature field and current field distribution of the two fuses are obtained from the simulation results.Taking the time of the maximum temperature point of the melt to reach the vaporizing point of the metal material as the reference,the pre-arcing times of the two fuses are 2.54 s,0.92 s respectively.The simulation results are compared with the pre-arcing time current curve.The error is 2.4% and within the allowable range,and the feasibility of the calculation model is verified.Then,the arc process of expulsion fuse is analyzed by using the ablation control arc,which includes the whole process of arc ablating the wall and gas extinguishing the arc.The two zone arc model in the tube is used to analyze the mass and the energy change of ablation control arc of the expulsion fuse.At the same time,the critical current density of the gas production of the two kinds of fuses is calculated under the action of the current generated energy by using the semi empirical formula.The paper analyzed the effects of gas decomposition on the arc extinguishing.The influence of different gas producing materials and different arc extinguishing gases on arc extinction process are analyzed.Finally,the breaking test is carried out according to the test requirements of the national standard GB15166.3-2008.From the waveform of the breaking test,the data of the pre-arcing process and arc process is extracted.The pre-arcing time,arc time and the whole breakingtime are calculated.The pre-arcing times of the two fuses are 2.644 s and 0.931 s.Compared with the simulation results,the error is within the allowable range,and the feasibility of the simulation method is verified again.This paper analyzed the pre-arcing process and arc process of overload current fault of the high pressure expulsion fuse comprehensively.The feasibility of simulating the pre-arcing time of the fuse on overload current is verified by the experimental study.It provides a new research method for the development of fuse products.This has important theoretical significance and application value to improve the performance of the expulsion fuse interrupting the overload current.