Electric field requirements for charge packet generation and movement in XLPE

The advent of experimental techniques capable of directly measuring the density of space charge in insulators under voltage in a non-destructive manner has revealed the existence of charge packet formation at high DC fields. In these circumstances space charge is observed to cross the insulation in the form of a packet rather than through the steady advance of a charge front. Such packets have been observed both in cable insulation, and in thin films. Since they occur at high fields before an electric failure occurs they are of interest as a possible pre-breakdown phenomenon. For this reason there is an interest in understanding the phenomena. In the experiments reported here we explore the electrical conditions required for the initiation of very slow moving charge packets in XLPE