Analysis of gaseous decomposition products of polyethylene exposed high fields and partial internal discharges

Although it is well known that divergent electric fields, such as produced by the needle-plane geometry, will generate tree-like breakdown channels that, in time, penetrate the dielectric, such channels are not seen under uniform field conditions. Further, it is also known that the electrical treeing process is accompanied by internal discharges which are readily detected by electrical and optical means [1,2]. It was of interest to learn if the route to breakdown under uniform and divergent field conditions involved similar decomposition processes in the dielectric. A mass spectrometer was employed to detect the gaseous species emitted by samples exposed to high AC stresses applied in a vacuum chamber attached to the spectrometer head.