Study on the properties of low dielectric loss composite insulating materials for superconducting cables
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摘要: 超导电缆相比于传统电缆具有导体无电阻损耗、传输容量大、可靠性高等优势，但作为其主绝缘的聚丙烯层压纸因具有较高的损耗因数导致超导电缆运行中的介质损耗大，增大冷却系统的负荷。采用具有低损耗因数的聚四氟乙烯滤纸取代聚丙烯层压纸中的牛皮纸层，通过热压法与聚丙烯膜形成具有两侧多孔可浸润液氮的三明治结构复合绝缘，测试结果表明超导电缆中以聚四氟乙烯/聚丙烯复合材料取代聚丙烯层压纸作为主绝缘，将使介质损耗降低一半以上。同时，由于聚四氟乙烯/聚丙烯复合材料与高温超导电缆中作为冷却剂的液氮间更小的介电常数差异以及液氮击穿的体积效应，采用具有更小孔径的聚四氟乙烯滤纸制成的低介损复合绝缘具有更强的抗局部放电的能力和更高的交流绝缘击穿强度，可极大提升高温超导电缆的绝缘可靠性。Abstract: Compared with traditional cables, superconducting cables have the advantages of no resistance loss, large transmission capacity and high reliability. However, polypropylene laminated paper as its main insulation has high loss factor, which leads to large dielectric loss in the operation of superconducting cables and increases the load of cooling system. In this paper, polytetrafluoroethylene filter paper with low loss factor is used to replace the kraft paper layer in the polypropylene lamination paper, and a sandwich structure composite insulation with porous surface can be formed by being hot-pressed with the polypropylene film. The test results show that replacing the polypropylene lamination paper with polytetrafluoroethylene/polypropylene composite material as the main insulation in the superconducting cable will reduce by more than half the dielectric loss. At the same time, due to the smaller dielectric constant difference between the polytetrafluoroethylene/polypropylene composite material and the liquid nitrogen used as the coolant in the high temperature superconducting cable and the volume effect of liquid nitrogen breakdown, the low dielectric loss composite insulation made of polytetrafluoroethylene filter paper with smaller aperture has stronger resistance to partial discharge and higher AC insulation breakdown strength, which can greatly improve the insulation reliability of the high temperature superconducting cable.
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图 1 局部放电起始电压和绝缘击穿电压测试实验装置示意图
Figure 1. Schematic diagram of partial discharge initial voltage (PDIV)and insulation breakdown voltage test apparatus
图 2 具有不同孔径的聚四氟乙烯/聚丙烯复合绝缘表面和界面扫描电镜照片
Figure 2. SEM images of the surfaces and interface of PTFE/PP composite insulation with different apertures
图 3 50 Hz下液氮中聚丙烯层压纸和聚四氟乙烯/聚丙烯复合绝缘的极化特性
Figure 3. Polarization properties of PPLP and PTFE/PP composite insulation in LN2 at 50 Hz
图 4 液氮中聚丙烯层压纸和聚四氟乙烯/聚丙烯复合绝缘的局部放电起始电压对比
Figure 4. Comparation of the partial discharge inception voltage between PPLP and PTFE/PP in LN2
图 5 复合绝缘体系与独立物质组合的转化示意图
Figure 5. Conversion of composite insulation system to separate material combination
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