聚酰亚胺在低温真空环境下的直流电气特性

DC Electrical Characteristics of Polyimide at Cryogenic Temperature in Vacuum

大型超导磁体等超导设备的绝缘系统是必不可少的一个重要部分,运行在液氦或液氮温区附近的绝缘结构失效是引起大型超导装置和设备故障的主要原因。利用自行研制的低温电介质电气特性测试系统,以聚酰亚胺材料为测试对象,研究了其在低温、真空环境下的直流击穿和沿面闪络特性。研究表明,与常温下相比,聚酰亚胺材料低温下的击穿场强有所提高,温度、厚度以及结构不同,其提高程度有所差异。聚酰亚胺材料的沿面闪络场强随着闪络次数的增加而略有增大,并趋于某一稳定值;温度对于首次闪络场强基本无影响,而对于稳定闪络场强,在78~200K范围内基本不变,在225~250K温度区域有所下降,此后又随温度的升高而上升。研究获得的低温真空下绝缘特性相关基础数据可用于低温真空放电特性的探索,为大型超导设备的可靠设计和运行提供参考。

The insulation system of large superconducting magnets and other superconducting devices is an indispensable part,the invalidation of insulation structure which is working at the temperature of liquid helium or liquid nitrogen is the main reason of the failure of large-scale superconducting equipment.By using the home-made test system which is developed for testing cryogenic electrical characteristics of dielectrics,a series of tests for studying polyimide films’ DC breakdown and surface flashover characteristics have been done at cryogenic temperature in vacuum.The test results show that the breakdown field strength of polyimide at cryogenic temperature has increased compared with at room temperature and the temperature,thickness and structure of polyimide all have some influence on the breakdown characteristics.And the surface flashover field strength of polyimide increase slightly with the flashover times and then trend to be a stable value.The temperature has almost no influence on the first-time flashover field strength of PI,but has definitive influence on the stable value of PI’s flashover field strength.In the range of 78~200K,the value maintained unchanged while in the range of 225~250 K,the value dropped a little and then increased with temperature rising.The relevant data of insulating properties at cryogenic temperature and vacuum based on the research not only can be used for the exploration of the discharge characteristics at cryogenic temperature and vacuum,but also provide a reference for a reliable design and operation of large superconducting equipment.