Research On Performance Of Breakdown And Surface Flashover For Insulation Of Cold Insulation HTS Cable

Because the HTS cable has the advantages of big current-carrying capacity, and small volume, its transmission capacity will be 3-5 times higher than conventional cable, and its cable joule heat loss is almost zero. So relative to the conventional cable, it has a great advantage that makes HTS cable rapidly concerned. Superconducting cable insulating material is an important part that has the vital significance for the economic and technical index and operation reliability of the equipment. Low temperature high voltage insulation technology is one of the key issues in the process of superconducting power technology development moving in the high voltage. Now insulating properties of the new film and winding insulation have few studies under liquid nitrogen. In this paper, breakdown and flashover performance of the different mediums including the new type film in liquid nitrogen is studied; at the same time, breakdown performance of lapped insulation in liquid nitrogen were studied; at last, relevant design factors of HTS cable insulation are state. These research results provide a reference for the design of cold insulation HTS cable insulation.AC and DC breakdown performances of different film dielectrics are researched in room temperature and liquid nitrogen by using the column-plate electrode. It draws the following conclusions:the dc breakdown performance of dielectric is much better than its ac breakdown performance; the breakdown strength of dielectric in liquid nitrogen is higher than that at room temperature; the dielectric sheets 150FCR019, 100CR,150FN019, and 100HN listed in descending order of AC breakdown strength in liquid nitrogen:100HN,100CR,150FN019,150FCR019; the dielectric sheets 150FCR019,100CR,150FN019, and 100HN listed in descending order of dc breakdown strength in liquid nitrogen:100CR,100HN,150FCR019,150FN019; breakdown strength of T418 is higher than T410 in liquid nitrogen. Compared with PPLP, its dc breakdown strength is bigger than that of PPLP, but its ac breakdown strength is smaller than that of PPLP. Through the analysis of doping on the properties of dielectric dc breakdown influence mechanism, it is concluded that dc breakdown performance of hybrid film is superior to the corresponding non-hybrid film in liquid nitrogen, because the trap density of hybrid film makes function that space charge limited current enhance. The ac breakdown test of the single and three layers PPLP in liquid nitrogen by using the column plate electrode is did and the mechanism of single layer and three layer film breakdown is analyze. It is concluded that single breakdown strength is greater than that of three layers. This is because the discharge of the liquid nitrogen between layers for three layers PPLP makes breakdown performance degradation.By studying the surface flashover performance of different dielectric materials in liquid nitrogen under the stainless steel and brass electrode, it is concluded that the dc flashover voltage resistance performance of T410 is superior to 100HN and T418 under the stainless steel electrode; the dc flashover voltage resistance performance of 100HN is superior to T410 and T418 under the brass electrode; Through the analysis of influence mechanism of electrode materials on creepage flashover performance of medium, for the same medium, flashover voltage under brass electrode is higher than that under stainless steel that is mainly because the electron work function of brass is bigger. In Liquid nitrogen, the impact resistant performance for 100HN is better than that of 100CR and it may be because the conductance performance of the 100 CR is better than 100 HN. By carrying through experimental investigation of development process for surface discharge about 100HN and 100CR by using triangle-to-plane electrode, the flashover discharge process of 100HN is divided into initial discharge stage discharge development stage and dangerous discharge stage, and the flashover discharge process of 100CR is divided into initial discharge stage, electronic multiplication stage and space-charge-limited current stage.The breakdown voltage of lapped insulation which respectively composed of single and composite insulation under liquid nitrogen is tested. For lapped insulation which composed of single insulation, withstanding ac and dc breakdown performance of lapped insulation which composed of 100HN is better than that of lapped insulation which composed of 100CR; withstanding ac and dc breakdown performance of lapped insulation which composed of 150FN019 is better than that of lapped insulation which composed of 150FCR019. The positive impulse voltage resistance of 100 HN lapped insulation is less than that of 100CR lapped insulation but negative impulse voltage resistance of 100HN lapped insulation is better than that of 100CR lapped insulation; The positive impulse voltage resistance of 1507N019 lapped insulation is less than negative impulse voltage resistance of that but negative impulse voltage resistance of 150FCR019 lapped insulation is lower than positive impulse voltage resistance of that. For lapped insulation which composed of composite insulation ac and dc breakdown performance for the first of type 2 and type 3 lapped insulation is the best; for type 4 lapped insulation, ac breakdown voltage of the second kind of lapped insulation is the biggest and DC breakdown voltage of the fist kind of lapped insulation is the largest; in the four types of lapped insulations, voltage resistance for the first kind of type 2 lapped insulation is the best. Through the analysis of lapped insulation breakdown path, it is concluded that AC/DC breakdown point of lapped insulation are largely on its edge, mainly because the edge of the field intensity is relatively large, at the same time, the liquid nitrogen of the gap in lapped insulation have very important influence on the breakdown position and the breakdown performance.For cold insulation HTS cable main insulation design, the following aspects needs to be considered:insulation material selection, the determination of withstand voltage, the determination of design field, the determination of the thickness of the insulation and the test of electric insulation performance of design sample. At the same time, the effects of quench on design field need to be considered.