Observations on Structural Changes under Thermal Ageing of Cross-Linked polyethylene Used as Power Cables Insulation

ABSTRACT Key Words: Observations on Structural Changes under ThermalAgeing of Cross-linked Polyethylene Used AsPower Cables Insulation Larbi Boukezzi 1 , Ahmed Boubakeur 2 , Christian Laurent 3 and Mouhamed Lallouani 4 (1) Department of Electrical Engineering, University of Djelfa,17000, Algeria(2) L.R.E./High Voltage Laboratory, Polytechnic National School, B.P182EL-Harrach, Algiers, Algeria(3) Electrical Engineering Laboratory, Paul Sabatier University, 31062 ToulouseCedex 4, France(4) ENICAB, Industrial Zone, Biskra, AlgeriaReceived 2 April 2008; accepted 9 August 2008 T he widespread use of cross-linked polyethylene (XLPE) as insulation in the man-ufacturing of medium and high voltage cables may be attributed to its outstand-ing physical, chemical, mechanical, and electrical properties. However, it is wellknown that degradation under service conditions is the major problem in the use ofXLPE as cables insulation. Especially, thermal oxidative degradation produces lowmolecular weight and oxygenated products. Several diagnostic measurements havebeen used in this study in order to characterize XLPE behaviour under thermal ageing.Firstly FTIR has been conducted on fresh and aged samples in order to reveal theeffect of thermal ageing on the chemical changes which take place in the XLPE struc-ture. The main changes are the formation of carbonyl groups (aldehyde, ketone, etc.).Use of DSC analysis shows the effect of ageing on the melting peak temperature T