Preparation and corona-resistance characteristics of double-layer polyimide/Al<inf>2</inf>O<inf>3</inf> nanocomposite film

Abstract

Polyimide (PI) film is widely used in inverter-fed motor as a kind of insulation material for its good performance at thermal, mechanical and electrical properties, while polyimide should bear corona discharge under the effect of bipolar continuous square impulse voltage (BCSIV) at poor working environment, and corona discharge is the key factor that causes failures in insulation system of motor. In order to improve corona resistance of PI film, a kind of double-layer PIMI2O3 film (PI/Al 2 O 3 -pure PI) was prepared by modified in situ method, and experiment of corona aging under BCSIV with rod-plate electrode system that designed according to standard of ASTM 2275 01 was carried out. The scanning electron microscopy (SEM) shows that nano alumina disperses homogenously in film and evident layered-structure can be observed with approximately same thickness for each layer. In comparison to pure PI film, monolayer PI/Al 2 O 3 and double-layer PI/Al 2 O 3 film exhibit better corona resistance. In addition, despite monolayer or double-layer, surface that bears discharge decides the corona-resistance performance. For double-layer film, there is significant difference between situations when nano side faces corona discharge and pure-PI side faces corona discharge. Incorporation of nano alumina can increase surface conductivity of film significantly and help improve corona resistance of film. Furthermore, the difference for corona-resistance performance was discussed.