Effect of temperature on polyimide dc flashover characteristics in different vacuum degrees

Abstract

The properties of electrical insulation in vacuum and at cryogenic temperatures are important for designing the insulation of large, low-temperature superconducting devices. Particularly, gas pressure and temperature turbulence could easily lead to insulation failure. In this paper, the results of measurements that reveal the dc flashover characteristics of polyimide film from 300 to 20 K at helium pressures of 10 −3 -10 3 Pa were reported. The results show that, in high vacuum, the flashover voltage is generally independent of pressure. As pressure increases, the flashover voltage first decreases and then increases gradually. Electron multiplication in helium or on the surface of PI is the main factor affecting flashover. For high to medium vacuum, the N (gas molecular density) at which electrons begin to collide with helium and reduce flashover voltage at higher temperature is less than at cryogenic temperatures. For medium to low vacuum, by comparing the flashover curve with a curve fit based on Townsend discharge theory, a result was found that when a certain specific N is exceeded, the electron impact ionization on the solid surface will no longer be the main influencing factor of flashover. This N increases as temperature decreases except 200 K, and reaches the minimum at 200 K. After analysis, it may be the larger mean free path of electrons increases the likelihood of electron impact ionization on the PI surface. Therefore, in order to maintain a high flashover voltage in engineering, it is necessary to maintain a higher degree of vacuum at higher temperatures; and when the pressure rises to low vacuum, the flashover is mainly determined by the gas discharge.

Study on surface discharge of nonlinear conductive epoxy resin/SrTiO3 composites in 80–300 K temperature zone

“…It was found that nano Al 2 O 3 was more effective than nano TiO 2 in enhancing both partial discharge inception voltage (PDIV) and flashover voltage [20]. Tu et al studied the effect of vacuum on flashover in the temperature range of 300-20 K and found that flashover at lower vacuum conditions is mainly determined by gas discharge [21]. Rodrigo et al studied the flashover characteristics of the He-epoxy resin (He-EP) interface at different temperatures.…”

“…Tu et al. studied the effect of vacuum on flashover in the temperature range of 300–20 K and found that flashover at lower vacuum conditions is mainly determined by gas discharge [21]. Rodrigo et al.…”

DC Surface Flashover Characteristics of Polyimide Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Main Chains under Vacuum

“…In a low-temperature superconducting device, the superconducting magnet needs to be installed in the vacuum cavity to maintain the low-temperature environment in the liquid helium temperature region, so most of its insulating structures are in a high vacuum working environment. According to statistics, when the insulation system of the superconducting magnet fails, the polyimide as its insulating structure will have discharge phenomena such as surface flashover or even body breakdown, which is one of the main reasons for the failure of superconducting magnets [2]. When polyimide is used as an insulating material in a spacecraft, due to the combined effects of the rapid transformation and gradient distribution of high and low temperatures in space, high-energy charged particles, atomic oxygen [3], and the plasma environment, these external incentives will eventually lead to the phenomenon of surface flashover discharge in the aerospace environment of the polyimide insulating medium, and its insulating properties will be seriously damaged, which will lead to the failure of spacecraft components [4,5].…”