The effects of cathode electrodeposited polymer film on the long vacuum gap breakdown

Abstract

Vacuum surface discharge is one of the most important issues for vacuum insulation. In this paper, a method for breakdown field strength enhancement of long vacuum gap is put forward, through depositing polymer dielectric coating on the electrode surface. The physical mechanism that the polymer film changes the electrode surface state is analyzed. After a layer of polymer film is deposited on the electrode surface, the decreased surface field strength and improved micro-surface state both help to suppress the field electron emission from the cathode. The technique of cathode electrodeposition for high polymers such as epoxy resin (ER), epoxy acrylate (EA), polyimide (PI) and poly(ether-ether-ketone) (PEEK) was explored, and the thickness of the electrodeposited coating can reach 20–50 µm. The effects of the electrodeposited polymer coatings of electrodes on the 2.5 cm vacuum gap breakdown were studied under a high-voltage vacuum experiment platform. Experimental results showed that when ER, EA and PEEK coatings with thickness of 25–45 µm were respectively electrodeposited on the 95 cm2 plate cathode, the initial-breakdown field strengths of the 2.5 cm vacuum gap were enhanced by 20.7%–22.4%. The enhancement of the initial-breakdown field strength was restricted by the coating defects, grain boundary defects on the cathode surface, and the micro-triple-point emission after the fusing of some local coating points due to the electron bombardments.