Research On Dynamic Voltage Distribution Characteristics And Regulation Methods Of Series-connected Vacuum Circuit Breakers

Circuit breakers are an important part of the power system.As an electrical insulating dielectric of circuit breakers,SF₆ has been widely applied in high voltage switch equipment above 110k V.SF₆ is a greenhouse gas.So,reducing and replacing SF₆ gas is an urgent task in the power field.At present,vacuum circuit breaker composed of breaks in series is one of the main research directions,but the problem of unbalanced voltage distribution has not been completely solved.Parallel grading capacitors could improve voltage distribution.However,excess grading capacitance could cause reburning.Besides that,the current amplitude is high and the duration is long during re-burning.In order to overcome this problem,on the premise of minimizing grading capacitance,the dynamic voltage distribution characteristics in the breaking process of series vacuum circuit breakers should be studied further.It is important to find the influence factors of dynamic voltage self-sharing and adjust them reasonably,so as to improve the voltage distribution and decrease grading capacitance.In this paper,the theory of dynamic voltage distribution characteristics during the breaking process was explored firstly.The regulation of different arcing stages of series vacuum circuit breaker on post-arc dynamic voltage distribution was revealed theoretically.The effects of arcing time,breaking speed,magnetic field and other factors on ion concentration and ion velocity were studied from the perspective of micro particle motion characteristics.At the same time,each break is limited by the equal current.The ion velocity of different breaks is different and the probability of charge exchange in particle collision is different.Then,the ion concentration will be dynamically adjusted.The relationship between dielectric recovery and dynamic voltage distribution was analyzed by Langmuir probe model.The conclusion is obtained that the change of post-arc charge and equivalent capacitance of break is caused by the difference of dielectric recovery process.A grading method to improve the post-arc voltage distribution by changing the arc state in the arcing stage is proposed.Under the guidance of dynamic voltage balance theory,the mechanism of different arcing time on voltage distribution was studied.The voltage distributions under different arcing time were explored and arcing modes to balance voltage distribution were found.The experimental platform of the synthetic circuit with vacuum circuit breakers in series was built to study the voltage distribution under the same arcing times and different arcing times.The experimental results show that arcing times of two breaks were synchronously reduced from 6.6ms to3.4ms and the voltage distribution unbalance decreases from 11.4%to 2.7%,under the condition of paralleling lower grading capacitance.The combination of different arcing times can improve the unbalance of voltage distribution.Shortening the arcing times can balance the voltage distribution in the rising stage of transient recovery voltage.On the premise of constant arcing time,the regulation effect of breaking speed on the voltage distribution of series vacuum circuit breakers in the same vacuum environment was explored.The electromagnetic simulation model of the double-break vacuum circuit breaker was established.The influence of breaking distance under different breaking speeds on static voltage distribution was studied,which provided a reference for the research of dynamic voltage distribution.In the synthetic circuit experimental platform,the voltage distributions at the same speeds and different speeds were studied.The arcing time of both breaks is 5ms.With the breaking speed increasing synchronously,the voltage distribution is more uneven and the voltage distribution unbalance increases by 7.7%.If different speeds are adopted for breaking,the breaking speed of the high-voltage break is slower than that of the low-voltage break,which is conducive to the voltage distribution and the minimum voltage unevenness can be reduced to 0.2%.In order to explore the regulation effect methods of magnetic field on voltage distribution,it is necessary to find effective magnetic field regulation measures.In the synthetic circuit,Helmholtz coil was used to apply an axial magnetic field between each gap consistent with the magnetic field direction of the contact.The effects of magnetic induction intensity and application time on the voltage distribution of series vacuum circuit breaker were experimentally studied.The results show that the magnetic field intensity remains unchanged before the current crosses zero and the closer the magnetic field is applied to the current zero,the more balanced the voltage distribution is.If the application time remains unchanged and the magnetic field intensity increases,the voltage distribution unbalance decreases first and then increases.Under the experimental conditions of this study,when the magnetic field is applied 3ms before current crossing zero and the magnetic field strength is 60m T,the voltage distribution is the most uniform.In addition,the voltage distributions of asynchronous breaking with and without magnetic fields were experimentally compared.It is concluded that magnetic field regulation can effectively improve the voltage distribution of asynchronous breaking.In a word,a method of regulating the dynamic voltage distribution in the post-arc stage by changing various influencing factors in the arcing stage is proposed in this paper,which is based on lower grading capacitance.The regulation methods of balancing voltage distribution of series-connected vacuum circuit breakers are obtained.