Effect of heat-treatment and sample preparation on physical properties of XLPE DC cable insulation material

• Published in: IEEE transactions on dielectrics and electrical insulation Vol. 23; no. 5; pp. 2508 - 2516
• Main Authors: Ghorbani, Hossein, Saltzer, Markus, Abid, Fahim, Edin, Hans
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cable insulation; Cables; conductivity; cross linked polyethylene insulation; Cross-linked polyethylene; Crosslinked polyethylene; Crosslinking; DC power transmission; Degassing; Dielectric devices; Dielectric loss; dielectric losses; Dielectric measurement; Effect of heat treatments; Electric conductivity; Electric space charge; Electrical properties; Extrusion; Film preparation; Heat treatment; Heating; HVDC insulation; HVDC power transmission; Insulating materials; Insulation; Molding (process); Morphology; Peroxide decomposition; Physical properties; Plastic bottles; Polarization properties; Polyethylene terephthalate; Polyethylene terephthalates (PET); Polyethylenes; Positron emission tomography; Power cables; power cables insulation; Pressing; sample preparation; Space charge; Telecommunication cables
• ISSN: 1070-9878; 1558-4135; 1558-4135
• DOI: 10.1109/TDEI.2016.7736807

Power cables with extruded crosslinked polyethylene (XLPE) insulation are used in HVAC and HVDC applications. These cables usually go through a degassing process to remove the methane formed in XLPE during the cross-linking reactions. In case of HVDC cables, the general belief is that the polar peroxide decomposition products (PDP) content significantly influences the conduction and space charge behavior of XLPE. This belief is mainly based on the results of experiments made on thin XLPE samples with different heat-treatments; but since heat-treatment also influences the morphology of the polymer, it is necessary to consider this effect as well. It is common to use polyethylene terephthalate (PET) film as a protective layer during sample press molding. Studies on the influence of the pressing film on the electrical properties of the sample are rare. In this work, the results of a series of experiments performed on 0.5 mm thick XLPE plaque samples in reference to additive free LDPE samples with different heat-treatment times are presented. Beside the PDP content, the morphology, DC conductivity and polarization properties are studied and analyzed. It was found that the pressing film used during sample preparation has a significant effect on the results and if not corrected, it may lead to wrong conclusions about the influence of the PDP content. Eliminating the effect of the pressing film, no clear correlation between the DC conductivity, dielectric loss and the PDP content was observed. The relation between the PDP content and DC conductivity is not found to be obvious, hence this correlation may need to be further evaluated.