Space Charge in Electron-Beam Irradiated Cross-Linked Polyethylene (XLPE): Charge Implantation and Release from the Bulk

Abstract

The aim of the present work is to study the dynamics of the space charge in crosslinked polyethylene (XLPE) induced by electron beam irradiation. For this purpose three energies have been chosen so as to implant charges in a controlled way, in the volume, at different depths not too close to the electrodes. Pulsed Electro Acoustic (PEA) method was used to measure space charge in each sample, at the end of the irradiation process, in ambient conditions. The space charge measurements show the existence of two electron implantation sites after irradiation, one in the bulk at a depth depending on the irradiation energy and the other near the irradiated surface and a fixed position (25 µm). The application of the electric field shows that the charge implanted in the volume tends to be evacuated during the polarization. The charge accumulated persists during the relaxation and is stable after 1 hour. The current measurements reveal the impact of the irradiation in XLPE sample: the steady current measured on the irradiated sample is substantially higher compared to the one recorded on the non-irradiated specimens. Also a change in conduction mechanism is observed. The current recorded on XLPE irradiated weakly diverges from linearity with the electric field in the field range up to 40 kV/mm.

Dynamic of a Space Charge in Gamma-Irradiated Cross-Linked Polyethylene (XLPE)

“…All profiles shown in this work are with 3 min interval time recording. As reported in previous work [11], the dominant mechanism observed on the recorded profiles for nonirradiated XLPE is the injection of charges followed by trapping near the electrode, forming homocharge. We clearly observe an injection of negative charge from the ground electrode, and the injection and charge accumulation processes are continuous during 1 hour stressing time.…”

“…Compared to irradiation by an electron beam, where primary electrons were deposited and the deposited dose was not homogeneous along the thickness [11], gamma-rays are much more penetrating, producing homogeneous irradiation. As seen in Fig.…”

“…Space charge profile recorded on a non-irradiated XLPE, during 1 h of relaxation in Volt-off[11]. Electric field distribution profiles recorded on a non-irradiated XLPE.…”

Space Charge in Gamma and Electron-Beam Irradiated XLPE

“…2 (a) shows space charge measurements on virgin XLPE done for 1 hour under polarization with a DC field of 40 kV/mm. As previously described [13], The injection of negative charge is the major mechanism found on the recorded profiles. The negative charge injected builds up with time, followed by trapping near the ground electrode.…”