Experimental Research On The Evolution Characteristics Of Medium Vacuum Arc Form During DC Breaking

With the rapid development of flexible DC transmission technology,DC power grids have become an important direction for future energy development,and DC circuit breakers(DCCB)are the key equipment for building DC power grids.The DCCB using vacuum as the arc extinguishing medium,which has obvious advantages due to its strong arc extinguishing capability.The morphological distribution characteristics of the vacuum arc will affect the initial plasma parameters of the post-arc process,and thus affect the recovery process of the medium strength of the arc.Compared with power frequency interruption,the arc diffusion time in DC interruption is shorter and the current reduction rate is higher.Therefore,DC interruption puts forward more stringent requirements on arc morphological characteristics.This paper investigates the evolution characteristics of the DC interruption process.In order to study the dynamic characteristics of DC vacuum arc,the experimental programs are designed and a vacuum arc test and observation platform is set up.Combined with the processing method of the arc image,the duration of the arc contraction state is quantitatively analyzed.The results show that the duration of the initial contraction state(tc)is approximately linearly increasing with the current and current amplitude at the moment when the arc starts.When comprehensively considered,tc increases slowly when the current is small.As the current continues to increase,tc increases significantly.The larger the opening speed,the shorter the duration of the contraction state,and the this phenomenon is more obvious at high current.There is a critical axial magnetic flux intensity Bmax.When the axial magnetic field is less than Bmax,Bz promotes the transition from a contracted arc to a diffused state.When the axial magnetic field is greater than Bmax,Bz instead prevents the contracted arc from spreading.The value of Bmax is 60 m T according to the experimental data.In the process of arc extinguishing,the arc will change to a fully diffused state when the power frequency current is zero,and then gradually extinguished.When the commutation current frequency is 864 Hz and 1521 Hz,the distribution of the arc column shape lags significantly behind the change of the arc current.Due to the obvious restraint of the residual magnetic field,the arc shape remains unchanged until the current decline to zero during the entire commutation process.The research results in this paper can provide some guidance for the design of the structural parameters of the contacts of the vacuum DCCB,as well as the input time of the reverse current,parameters of the commutation circuit and the selection of the operating mechanism parameters.