F6.1.03 9th International Conference on Insulated Power Cables F6.1.03

Jicable'15 - Versailles 21-25 June, 2015

Dielectric strength of γ-radiation cross-linked, high vinyl-content po lyethylene

M. G. ANDERSSON (1), M. JARVID (1), A. JOHANSSON (2), S. GUBANSKI (2), M. FOREMAN (3), C. MÜLLER (1)*, M.R. ANDERSSON (1),(4)*

1 Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, 41296, Göteborg, Sweden, mattan@chalmers.se, christian.muller@chalmers.se,

2 Department of Materials and Manufacturing Technology/High Voltage Engineering, Chalmers University of Technology, 41296, Göteborg, Sweden, anette.johansson@chalmers.se, stanislaw.gubanski@chalmers.se

3 Department of Chemical and Biological Engineering/Nuclear Chemistry, Chalmers University of Technology, 41296, Göteborg, Sweden, foreman@chalmers.se

4 Ian Wark Research Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia, mats.andersson@unisa.edu.au

Low density polyethylene (LDPE) has become the material of choice for the electrical insulation of high-voltage cables due to a combination of low electrical losses and high breakdown strength. Typically, LDPE is cross-linked in order to ensure dimensional stability at high temperatures and to prevent stress cracking. Peroxide cross-linking is most common but results in unwanted by-products that must be removed by degassing for an extended period of time at elevated temperature. Moreover, these volatile peroxide decomposition products pose a considerable health hazard, which requires a suitably adapted work environment. Hence, alternative cross-linking concepts for polyethylene insulation are of interest for cable manufacturers.

We explore γ-radiation cross-linking of high vinyl-content low-density polyethylene (LDPE) and its potential use as a high-voltage insulation material. Of the three investigated resins containing 1, 0.5 and 0.17 vinyl groups per 1000 carbons, respectively, only the highest vinyl content material featured a sufficiently high gel content of more than 70% and hot-set elongation below 175%, when cross-linked with a γ-radiation dose of at least 68 kGy. Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) reveal that neither the crystallinity nor the lamellar thickness of the highest vinyl-content LDPE are negatively affected by γ-radiation cross-linking. As a result, we find that the dielectric

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