Research On Arc Morphology And Breaking Characteristics Of Intermediate-high Frequency Interruption In Vacuum Interrupters

In the power systems,the functions of breaking and closing are achieved by circuit breaker.Vacuum switch has some advantages of high speed of dielectric recovery,strong arc-extinguishing capability,long operating life,adaptability to environment and so on,making it one of the competitive choices in the field of intermediate-high frequency breaking and aerospace.Compared with the arc of power frequency,the intermediate-high frequency vacuum arc has the characteristics of short arcing time,considerable di/dt and high rise rate of recovery voltage which put forward further requirements on interrupters.The research of this thesis mainly focuses on the morphology and breaking characteristics of medium-high frequency arc in vacuum interrupters.Firstly,the theoretical model of medium-high frequency vacuum arc is calculated,the main factors that affect the interrupting ability of the chamber are analyzed.The results show that whether the vacuum arc is concentrated is mainly related to the rate of arc diffusion and the current rising.The faster the arc diffusing and the smaller the current increasing,the less likely accumulate of the arc.In the process of dielectric recovery,under the frequency of 1 kHz ~10 kHz,the larger the current amplitude and the higher the frequency,the smaller the arc distribution area and the slower the sheath growth rate.The lower the current frequency and the larger the amplitude,the smaller the initial value of metal vapor density.What’s more,the time of sheath growth is 1~2 orders of magnitude higher in intermediate-high frequency breaking than that of power frequency when the amplitude of current is similar,and the probability of restrike after arc is significantly increased.In order to study the dynamic characteristics of mid-high frequency arc,a intermediate-high frequency breaking experimental circuit and an arc shape observation system were designed to measure the morphology and experimental waveforms of vacuum arc,and the morphological parameters of vacuum arc were analyzed in combination with image digital processing methods.The experimental results show that when di/dt is less than 100 A/μs,the initial diffusion speed of arc is approximately proportional to di/dt,and then it has trend of saturation with the increase of di/dt.When the arc doesn’t spread to the entire contact surface,the maximum diameter of the arc is approximately proportional to the current amplitude,and inversely proportional to the current frequency.Through the fitting method,the formula of maximum arc diameter on the current frequency and amplitude is obtained.Finally,the breaking characteristic of vacuum interrupter at different frequencies is given.With the increase of the current frequency,the breaking capacity of the interrupter decreases.However,the breaking capacity of the interrupter does not change obviously when the frequency is higher than a certain value,which is 3 kHz in this thesis.