This paper investigates the changes in electrical and physico-chemical properties of lowvoltage power cables for nuclear application when subjected to the combined effects of gamma radiation and temperature. Electrical response is evaluated by means of the dielectric spectroscopy, while the physicochemical changes are analyzed at different structural scales through five complementary techniques (OIT measurements, FTIR spectroscopy, swelling measurements, DSC analysis and micro-indentation). The dielectric spectroscopy and the first two chemical techniques are shown to be appropriate for evaluating the development of radio-thermal ageing in low-voltage cables. Hence, the results reported in this article suggest the effectiveness of dielectric spectroscopy as a non-destructive technique for on-site cable diagnosis.

Surface charge accumulation on the spacers is one of the key issues restraining the development of HVDC GIS/GIL. The precise measurement of surface charge properties provides the basis for further study of the surface charge transport mechanism as well as the charge-induced flashover mechanism under DC voltage. In this study, the authors discuss their perspective on the current status, development needs and potential developing orientation of surface charge characterisation techniques. Different surface potential measurement methods and charge inversion algorithms are reviewed regarding the previous studies and future research needs. Drawbacks and outlooks of surface charge measurement techniques are also discussed with the background of laboratory experiment results and on-site measurements. It is hopefully that this study can serve as a useful guide reference for researchers within the same research field. More importantly, it is authors' hope that this study can inspire some novel ideas for readers into developing of more accurate and scientific interface charge characterisation techniques.

The radio-thermal ageing of silane-crosslinked polyethylene (Si-XLPE) was studied in air under different γ dose rates (6.0, 8.5, 77.8, and 400 Gy·h−1) at different temperatures (21, 47, and 86 °C). The changes in the physico-chemical and electrical properties of Si-XLPE throughout its exposure were determined using Fourier transform infrared spectroscopy coupled with chemical gas derivatization, hydrostatic weighing, differential scanning calorimetry, dielectric spectroscopy and current measurements under an applied electric field. From a careful analysis of the oxidation products, it was confirmed that ketones are the main oxidation products in Si-XLPE. The analytical kinetic model for radio-thermal oxidation was thus completed with relatively simple structure–property relationships in order to additionally predict the increase in density induced by oxidation, and the adverse changes in two electrical properties of Si-XLPE: the dielectric constant ε′ and volume resistivity R. After having shown the reliability of these new kinetic developments, the lifetime of Si-XLPE was determined using a dielectric end-of-life criterion deduced from a literature compilation on the changes in R with ε′ for common polymers. The corresponding lifetime was found to be at least two times longer than the lifetime previously determined with the conventional end-of-life criterion, i.e., the mechanical type, thus confirming the previous literature studies that had shown that fracture properties degrade faster than electrical properties.

This article presents the development and application of a modelling approach based on quantities obtained from mechanical and electrical tests to assess the aging of low voltage cable insulation for nuclear applications. In order to obtain experimental data needed for the establishing of the models, accelerated aging is performed on coaxial cables. The first part of this paper focuses on the development of a predictive modelling for mechanical properties; this allows the evaluation of the Dose to Equivalent Damage (DED) as a function of the aging stress (dose rate). However, the use of mechanical tests for cable aging assessment presents some problems, being such tests destructive for the insulation and potentially affected by local defects. The novelty of this work lays on the introduction of a new model, allowing the definition of the end-of-life point in terms of electrical non-destructive tests. The second part of this article presents the development of aging modelling of cable insulation and correlation with experimental data obtained at different stresses, which allow the estimation of the expected life of the cable under test to be derived from diagnostic measurements of electrical properties like, e.g, tan. Finally, the application of the proposed life model to two typical real-condition nuclear environments is presented and discussed.INDEX TERMS Modelling of insulations, LV cables, Nuclear cables, radio-chemical aging, predictive modeling, cable life modeling, polymer aging, extruded cables.

The usability of any material hinges upon its stability over time. One of the major concerns, focusing on polymeric materials, is the degradation they face during their service life. The degradation mechanisms are deeply influenced by the aging temperature to which the material is subjected. In this paper, low-density polyethylene (LDPE) flat specimens were thermally aged under two different temperatures (90 °C and 110 °C) and analyzed. Specimens were characterized through both the most common mechanical and chemical measurements techniques (e.g., tensile stress, thermal analyses, oxidation induction time) and electrical measurements (dielectric spectroscopy, in particular), which are examples of non-destructive techniques. As a result, a very spread characterization of the polyethylene-based materials was obtained and a very good correlation was found to exist between these different techniques, highlighting the possibility of following the aging degradation development of polymers through electrical non-destructive techniques.

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This paper investigates the evolution of electrical properties with aging for two XLPE based materials having different chemical compositions. It is shown that aging and material composition can significantly affect the electrical response, suggesting the suitability of dielectric spectroscopy for polymer diagnostics. Furthermore, the dielectric response is correlated with the evolution of mechanical properties, in particular elongation at break (EaB), in order to evaluate the possible scaling-up of the current cable qualification standard.

To investigate the effect of fluorination on surface electrical performance of ethylene propylene rubber (EPR), four pieces of EPR specimens are prepared and fluorinated for different duration ranging from 120 min to 480 min. The surface morphology and element compositions of experimental specimens are tested. The surface potential decay and complex permittivity are measured. The tracking discharge property and the erosion properties after tracking test are investigated. The surface charge transport and electrical property tailoring mechanism are discussed. The results show that when the fluorination duration is from 120 min to 360 min, the surface morphology gradually becomes flat and compact with time, and the surface resistance to electrical tracking is improved. While an excessive fluorination with the duration of 480 min leads to a significant increase in surface conductivity and a weakening in the resistance to electrical tracking, which is mainly due to a change in surface morphology. The recommended fluorination duration for an optimised surface property is between 240 and 360 min for EPR specimen.