| Compact structure,miniaturized size and stable operation are important development directions of pulsed power technology.Propylene carbonate(PC),due to its great permittivity,high dielectric insulating strength and wide range of environmental adaption,has a great potential in the capacitive-energy-storage pulsed power systems used as energy storage medium of the pulse forming line(PFL).The technical difficulty is to enhance the insulation strength.Therefore,it is of great academic and practical significance to investigate microsecond energy storage characteristics of propylene carbonate and its breakdown mechanism.The thesis mainly focuses on the polarity effect,additive effect,temperature adaptability and the PFL application of PC.And the PC-based PFL can be operated with free maintenance.The research results of this thesis have provided a solid foundation for the application of PC-based PFL in compact pulsed power source and showed the good development prospect.The main contents and research results of the thesis are shown as follows.(1)Effect of polarity on the pulse energy storage characteristics of PCBased on the optoelectric diagnostic technique,the pulse breakdown platform of liquid dielectric is built.And the research of the pulse energy storage characteristics,the polarity effect and streamer images of PC were carried out by solving synchronous trigger technical difficulties of the ultra-high speed camera.Experimental results show that the positive and negative breakdown voltage are 71 kV and 35 kV,respectively.It means that the positive breakdown voltage is 2 times of the negative one in the case of needle-plate electrodes whose gap is 5 mm.Optical diagnostic results show that both positive and negative streamers are propagated from the needle electrode to the plate electrode.And the streamer channel has a strong branching trend with certain random characteristics and self-similarity.The positive streamer has a filamentous structure,while the negative streamer is like a sparse tree.In the conditions of quasi-uniform field for spherical electrodes whose gap is 1 mm,the proportions of the streamer from the cathode,anode,liquid dielectric and all the others are 55%,15%,25%,and 5%,respectively.Moreover,a charge layer model based on the interface between the metal electrode and PC is proposed.Appling a bias voltage will change the potential state at the interface,resulting in the polarity effect.(2)Effect of additive on energy storage characteristics of PCResearch on the effect of pulsed energy storage characteristics when adding ethylene carbonate or xylene into PC was carried out.The results show that the appropriate additives can effectively improve the pulse energy storage characteristics of PC in the quasi-uniform field whose gap is 1 mm between electrodes.The breakdown voltage of mixture was increased by 27.2% and 53%,respectively,compared with pure PC,when adding 6.7% ethylene carbonate or 18.5% xylene,respectively,which was the optimum concentration.And the breakdown voltage stability also has a good improvement.In the non-uniform field,they made the negative breakdown voltage of PC increased,and its positive breakdown voltage decreased slightly,regardless of adding ethylene carbonate or xylene.Theoretical analysis shows that the strong electron affinity and inspiratory of two additives molecules impede the formation of the discharge channel,the mixture breakdown voltage becomes larger.(3)Effect of temperature on the pulse energy storage characteristics of PCBy using the temperature control chamber to precisely adjust the temperature of PC,effect of temperature on the pulse energy storage characteristics of PC was experimentally investigated.In the quasi-uniform field whose gap is 1 mm between electrodes,experimental results show that the breakdown voltage of PC increases with the increase of temperature.Compared to the breakdown voltage at room temperature,breakdown voltage at-50? decreased by 77% and it did not change significantly at high temperature.But there is no single linear relationship between the breakdown voltage stability and the temperature.In the non-uniform field,the breakdown voltage of PC also increases with the increase of temperature.While there is a turning point at 0?,which is mainly related to the moisture content.Changes of water molecules' state at 0? are the main reason leading to the turning point.Regardless of quasi-uniform field or non-uniform field,the brightness of the streamer is generally dark and small,and the branches are less at low temperature.However,the streamer is more variable,the main streamer is thicker and the branches are more at the high temperature.Theoretical analysis shows that the increase of the temperature makes the liquid fluidity and air solubility become larger.So,it is difficult to form a stable "bridge".Thus,the breakdown voltage becomes larger.(4)The pulse forming line application of PCBy using the integration system of purification for PC and vacuum infusion for PFL has achieved deionization,degassing and removing water and impurities of PC.The resistivity can be increased to 200 M?·cm and can remain above 30 M?·cm for 3 months.The results show that the breakdown voltage of PFL based on PC can reach 900 kV and the output power of the compact pulsed power source is 30 GW,and the maintenance-free operation is realized. |
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