Light emission from LDPE during electrical tree initiation

The characteristics of light emitted during the initiation of an electrical tree in low density polyethylene (LDPE) subjected to highly divergent fields have been studied. Needles having tip radii of between 3 and 10 µm were molded into the LDPE to create the divergent field. Light was not only detected in degassed specimens as reported by other workers but also in air-impregnated (normal) specimens as well as in those impregnated with other gases. The light characteristics of degassed specimens were found to be different from all others. It is proposed that the light from degassed specimens could be due to radiation from electron-hole recombination only whereas in all other specimens a combination of this and other radiative phenomena could be responsible. The tree inception voltage of specimens molded in air was found to be lower than that of specimens impregnated with inert gases. Based on the charge transfer at the electrode-polymer interface it is proposed that injected charges are responsible for the radiative phenomena observed. Some of the emitted light in turn could cause bond scissions and subsequent degradation of the polymer, leading to the formation of an electrical tree.