Study On The Breakdown Characteristics Of Glycerol Medium In The Repetitive Pulsed Mode And Its Applications In The Pulse Forming Line

With the development of pulsed power technology,the liquid dielectrics with high energy density and high breakdown voltage are applied widely in the pulse power systems.Especially the glycerin has the advantage of high resistivity,which do not need deionized circulating device in comparison with deionized water.So,glycerin can realize free maintenance,small leakage current and further apply in the low-voltage,long-charging time(tens of microseconds)pulse power systems.This paper studies the breakdown characteristics and the related mechanism of glycerin when it acts as pulse forming line(PFL)energy storage dielectric under the condition of tens of microseconds,and the contents include the following several aspects.(1)Study on free maintenance of glycerin PFLExperimental research is made on the resistivity characteristic of the glycerol in shrinkage ratio PFL,including the resistivity characteristics of the glycerol in a long time(500 days),the relationship between the resistivity characteristics and the charging time of PFL,resistivity characteristics of different liquid storage dielectric.Results show that the glycerol can maintain resistivity at a higher level in a long time,satisfy the requirement of long charging time(tens of microseconds),and can achieve free maintenance for a long period.Consequently,the glycerol owns the superiority which is not comparable to other liquid energy storage dielectric.(2)Research of the influence of bubbles in glycerol on the electric field distribution and insulation characteristics in the pulse forming line.Several forms of bubbles in the pulse forming line were analyzed and summarized by monitoring the change of bubbles in glycerol during the progress of experiments.And the effects of these forms of bubbles on the electric field distribution in the pulse forming line were discussed.Results show that the electric field distribution in the pulse forming line caused by different forms of bubbles has similar characteristics.The electric field inside the bubble is a uniform one that is higher than the background electric field;the electric field in glycerol outside the bubble perpendicular to the direction of the background field increases,and the electric field in glycerol parallel to the direction of the background field decreases.Higher electric field in bubbles may lead them ionize,hence,further analyze the effects of the ionized bubbles on the electric field distribution in the pulse forming line.Results show that ionization of bubbles results in the decrease of the electric field in the bubbles,the decrease of the electric field in glycerol inside the bubbles perpendicular to the direction of the background field,and the increase of the electric field in glycerol parallel to the direction of the background field,up to 3 times the intensity of the background field.This may be a crucial reason for the breakdown of the glycerin gap.To further reduce the influence of bubbles on the voltage withstanding capacity of glycerol pulse forming line,the pressure distribution in the degassing system of glycerol pulse forming line was analyzed.Reasons for the decrease of degassing efficiency were obtained,the degassing process of glycerol pulse forming line was optimized,and the degassing efficiency of glycerol pulse forming line was improved.(3)Study on deformation of bubbles and their effect on insulation in pulsed electric field with repetition frequency.It is found that there is deformation accumulation of bubbles in the pulse forming line through the high-speed video observation system.Analyzing the deformation characteristics of bubbles in the pulse electric field,we found out that the reason of deformation accumulation is bubbles could not return to its original form during the pulse interval time,and put forward a physical model about the breakdown of glycerol gap resulting from bubbles' deformation under the condition of the pulsed electric field with repetition frequency.Influence of intensity of the electric field,temperature,pressure,and pulse number on bubble deformation was further studied.The results show that the intensity of the electric field,temperature and pressure will affect the bubble deformation characteristics in a pulsed electric field with repetition frequency,and the influence of pulse number depends on the pulse interval and the bubble recovery time.The special deformation characteristics of the bubbles before the breakdown of the pulse forming line are also found in the experiment,which provides an effective basis for formulating the safe working field intensity of the pulse forming line.(4)Study on the insulation characteristics of glycerol in PFLUnder the conditions of single pulse and pulse repetition frequency,we study the breakdown characteristic of glycerol in shrinkage ratio PFL and obtain the change rule of glycerol breakdown field strength with factors(temperature,pressure,et al)in 25 ?s charging time,10 Hz,100 pulses.The change rule contributes to the reference for the design of further glycerol PFL.