Research On Breaking Characteristics Of Medium Frequency Arc In Vacuum Interrupter

DC circuit breakers used to achieve DC fault isolation and removal,it is an indispensable DC core network equipment.Mechanical DC circuit breakers using current injection,produced by LC high-frequency oscillation current reverse injection into the main loop,form the current zero cross to complete the break.The general conclusion that the vacuum medium relative to other types such as SF6,air,oil and others,the IF breaking capacity is bigger and transient recovery is faster,so the general choice of vacuum circuit breaker to complete the medium frequency current breaking.In this operating condition,the AC circuit breaker is interrupted in the frequency of kHz magnitude,the current of 10 kA magnitude,the arcing time of ms magnitude,and a large rate of rise TRV.Interrupter breaking capacity must be improved.In this paper,the medium frequency breaking characteristics of the vacuum interrupter is studied.First,through the establishment of single-frequency oscillation circuit and detachable interrupter device,the experiments on the cathode spot of the intermediate frequency arc were carried out.The effect of frequency on the distribution and velocity of arc cathode spots was studied.The relationship between the distribution of cathode spots and the frequency was analyzed.It was found that in the frequency range of 1000 ~ 2500 Hz,with the increase of frequency,the distribution of cathode spots is more concentrated,showing the area of the cathode spot becomes smaller.The distribution of cathode spots near the zero zone is the initial condition of the physical process after the arc.Because it directly affects the generation process of particles,and will have an impact on particle migration and diffusion after the arc.By establishing a CTM model that considers the influence of the arcing process,it is found that the dominant role of fast ions and slow ions in sheath growth is transformed as the frequency increases.When fast ions dominate and sheaths grow rapidly,In contrast,slow ions dominate and the sheath grows slowly,which is not conducive to arc breaking.Therefore,in the mechanical DC circuit breaker selection of the commutation current frequency,it should avoid the slow ions dominate frequency range.Through the transient simulation of arc,it is found that in the frequency range of 1000-2500 Hz,with the increase of frequency,the concentration of ions becomes larger,resulting in the slow growth of the sheath.Finally,the method of calculating the current breaking capacity of the circuit and the method of selecting the parameters of the circuit components under the constant current are studied.The CTM model considering the influence of the arcing process and the criterion of arc reignition are used to determine the limit of arc breaking and the optimal selection of the capacitance and inductance parameters.Through calculation,the breaking current limit under fixed parameters and the optimized circuit element parameters under fixed current can be determined,and the arc reignition time can be calculated.The research results of this dissertation can provide the basis for the design and reasonable selection of vacuum interrupter for mechanical DC circuit breakers,and gives the theoretical basis for the selection of the frequency range of the commutation current of the mechanical DC circuit breaker;the method of calculating the breaking current limit and the optimization of the parameters of circuit components.