The Role of Polymer Interface During Tree Initiation in LDPE

Based on charge transfer mechanisms at the polymer interface, it is bhown that the injected charges are responsible for the light emitted during tree initiation in LDPE subjected to highly divergent fields. Light was not only detected d 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 photoemission characteristics of degassed specimens were found to be different from all others and probably are due to radiation from electron-hole recombination. In all other specimens a combination of this and other radiative phenomena could be responsible. It is proposed that at low voltages the emitted light, which is mostly in the visible spectral range, is not immediately harmful to the insulator. It is only at high voltages that the emitted light would include more energetic and intense ultraviolet (UV) radiation and this UV could cause rapid degradation of the polymer and give rise to an electrical tree.