Electric field requirements for charge packet generation and movement in XLPE

Abstract

This is the unspecified version of the paper.This version of the publication may differ from the final published version. Permanent repository link ABSTRACTThe formation of space charge packets in XLPE (Cross-linked polyethylene) tapes from unaged cable insulation has been studied utilising the pulsed electro-acoustic (PEA) technique.The 150 m thick sheets were studied under constant applied dc field of 120 kV/mm at a temperature of 20 C for a period of 48 hours. After an inception period of about 3.5 hours, during which heterocharge accumulates at the anode and increases the local field there, a sequence of positive charge packets were observed to transit the sample starting from near the anode. This is shown as a moving image at the following web site: <include web site address here>. Calculation of the internal field showed that the packets required a field of 140 kV/mm for their initiation. Reduction of the applied field step-wise from 120 kV/mm to 80 kV/mm indicated that the charge packet would keep moving as long as the local field at its front exceeded 100 kV/mm, but with a reducing magnitude. A return to an applied field of 120 kV/mm confirmed that the local field required to initiate a new packet was in excess of 135 kV/mm. The results are discussed in terms of current theories of charge packet formation. The first packet appears to be a moving front of field ionisation. The generation of subsequent packets is governed by the field at the anode and the balance of charge See, Dissado and Fothergill 9/16/08 2:31 PM 2 injection and extraction process, which occur there. The nature of the negative charges produced at the ionisation front is not clear, but they are unlikely to be electrons.

Space charge formation and its modified electric field under applied voltage reversal and temperature gradient in XLPE cable

“…This will result in localised electric stress enhancement and even premature failure of the cable insulation when the localised fields exceed the design values [1][2][3]. This issue has stimulated the investigation of space charge accumulation and retention, and abundant data has been obtained from film and plaque samples over the past two decades [4][5][6][7][8][9][10][11]. However, less attention has been paid to space charge dynamics in full sized cables presumably due to a limited range of experimental systems suitable for examining cables.…”