Near UV emission during electrical tree initiation in LDPE

Abstract

Several mechanisms have been proposed for electrical tree initiation in high voltage (HV) transmission and distribution cables. These include fatigue cracking due to Maxwell stress, Joule heating that leads to thermal decomposition, high field induced impact ionization and hot electrons that can break bonds of the polymer insulation. These mechanisms acting singly or in combination can cause insulation failure but none of these has been able to adequately explain the gradual degradation that occurs in cables which operate at stresses much lower than the breakdown strength of the polymeric insulation. It has been reported that light is emitted when low-density polyethylene (LDPE) is subjected to highly divergent electric fields at cryogenic [l] and room [2] temperatures. Such fields can be produced by metallic inclusions or protusions in the polymer and are usually simulated by embedding needles into the polymer. It was shown recently [3] that the mechanism of charge transfer across the metal-polymer interface controls the voltage at which light inception occurs at the needle tips.