170 research outputs found

    Additive impact on space charge of XLPE-based insulators subjected to radio-chemical aging

    Get PDF
    This work investigates the development of space charge distribution through by means of the pulsed-electroacoustic method on differently-filled XLPE tapes subjected to radiochemical aging. The contribution of these different fillers on the space charge distribution and its evolution with aging is highlighted and linked with the physical-chemical properties (e.g. oxidation degree) of these materials

    Multiscale properties of polymeric insulating materials: from microscale polarizability to macroscale permittivity

    Get PDF
    This article presents an innovative and easy way for the calculation of the real part of permittivity for some of the most common insulating materials used for electrical applications, namely: polyethylene (PE), polypropylene (PP), polytetrafluorethylene (PTFE), ethylene-propylene diene monomer (EPDM), polyamide-imide (PAI), and epoxy resin (EP). This is achieved by the implementation and validation of the additivity approach for polarizability, along with the derivation of molecular volumes by means of chemical calculations involving real density of the considered materials. The proposed approach significantly reduces the computational time and effort for the calculation of macroscopic permittivity. Simulated values show good accordance with experimental results, thus validating the approach

    Broadband dielectric spectroscopy: A viable technique for aging assessment of low-voltage cable insulation used in nuclear power plants

    Get PDF
    This paper deals with the study of a non-destructive technique to detect the aging state of cable insulation used in a nuclear environment subjected to radiation and temperature aging. Cable samples were aged under dose rates ranging from 0.42 and 1.06 kGy/h at 55 and 85 °C. The imaginary part of the permittivity at 100 kHz is found to correlate well with mechanical properties, such as elongation at break, which is typically used to diagnose cable insulation, but it is a destructive property and cannot be used on field. It has been demonstrated also that a postirradiation effect occurs even years after aging is stopped, increasing the imaginary permittivity and worsening mechanical properties due to the slow conversion of radicals into oxidized species. The main consequence is that when cable insulation is subjected to a nuclear accident, releasing a huge amount of radiation, the health of cable insulation must be followed also for a long time after the accident occurred, since aging due to oxidation progresses even when the radiation source is switched off

    Development of analysis tools for structures protected by the damped cable system

    Get PDF

    Design and optimisation of damped cable system characteristics to suit application

    Get PDF

    Impact of additives and fillers on space charge behavior of polyethylene insulation: investigation and modeling

    Get PDF
    Diagnostic measurements on electrically insulating materials are a compulsory step to assure an acceptable service life of the electrical equipment. In particular, this paper focuses on the consequences of the implementation of several concentrations of antioxidants (Irganox® 1076 and Irganox® PSS02) inside Si-XLPE matrices. Thermally Stimulated Depolarization Current (TSDC) measurements were carried out on pure and filled samples to obtain information about the space charge behavior and trap distribution of the specimens. Postprocessing based on Randal-Wilkins model highlighted additive impact on Si-XLPE properties. Similar trap depth and different trap density values were found in samples with different concentrations of the same additive, suggesting a close correlation between the energy levels of localized states and the used antioxidants

    Effects of Graphene Coatings on hindering Space Charge injection in Epoxy Resin

    Get PDF
    The reliability of epoxy resins (and dielectrics in general) employed for HVDC applications is significantly affected by space charge accumulation in the insulating material. Several methods have been tested to limit the injection and accumulation of space charge. In this work, planar specimens featuring graphene coatings were tested. Measurements of space charge accumulation, conductivity and permittivity at different temperatures (from 30°C to 60°C) and fields (from 30 kV/mm to 50 kV/mm) were carried out on epoxy specimens with and without coatings. Results show accumulation of space charge for low fields and temperatures in the reference specimens, while a reduction can be noticed with a layer of graphene coating. On the other hand, at higher fields or temperatures, the effect is reversed

    Analysis on the impact of additives on space charge behavior of thermally aged XLPE plaques

    Get PDF
    This article investigates the space charge properties of XLPE-based materials characterized by different concentration and types of additives and fillers inside the polymeric compound. Materials were aged under three different temperatures (87 °C, 110 °C and 130 °C) for 24, 18 and 12 months, respectively. Space charge profiles of both unaged and aged materials were obtained through the Pulsed Electro Acoustic (PEA) method. Additives and fillers are proven to significantly impact the space charge behavior of the insulating material both in the unaged and aged states. The impact of antioxidants, together with their kinetics under thermal aging conditions, is analyzed and claims an effective containment of the degradation kinetics, keeping the accumulated space charge to low values

    Multi scale aging assessment of low-voltage cables subjected to radio-chemical aging: Towards an electrical diagnostic technique

    Get PDF
    In this article, the aging behavior of nuclear-grade low voltage cables, characterized by different geometries and insulation compositions, is investigated. Cables were subjected to radio-chemical aging at different dose rates (7 Gy/h, 66 Gy/h and 400 Gy/h), in order to simulate typical aging environments inside nuclear plants. The changes of insulation properties due to aging are investigated at different scales, aiming at highlighting possible correlations between molecular-scale properties and global macroscopic material behavior (e.g., mechanical and electrical ones). Microscale material behavior is investigated by means of FTIR spectroscopy and oxidation induction time (OIT) measurements, in order to evaluate material composition changes and material resistance to oxidation, respectively. On the other side, mechanical and electrical macroscopical properties are examined through tensile stress and dielectric spectroscopy measurements. It is found that aging is deeply influenced by the effect of additives (e.g. antioxidants) inside the insulation. In particular, the presence of antioxidants delays oxidation process allowing material modifications during the early aging states to be evaluated. Dielectric spectroscopy is demonstrated to properly follow all the stages of the degradation process, confirming its appropriateness as a non-destructive condition monitoring technique for cables. Finally, the evolution with aging of the dielectric response is associated with the variations of the considered chemical and mechanical properties, allowing the derivation of correlation master curves

    Immunity, Inflammation and Heart Failure: Their Role on Cardiac Function and Iron Status

    Get PDF
    Aims: Heart failure is a clinical syndrome characterized by subclinical systemic inflammation and immune system activation associated with iron deficiency. No data exist on the various activations of immune-mediated mechanisms of inflammation in heart failure patients with reduced/preserved ejection fraction. We aimed to (1) investigate possible differences in inflammatory parameters and oxidative stress, and (2) detect a different iron status between groups. Materials and Methods: We enrolled 50 consecutive Caucasian outpatients with heart failure. All patients underwent echocardiographic measurements, laboratory determinations, evaluation of iron status and Toll-like receptors, and NF-κB expression in peripheral blood mononuclear cells, as well as pro-inflammatory cytokines. All statistical calculations were made using SPSS for Mac version 21.0. Results: Patients with reduced ejection fraction showed significantly lower hemoglobin levels (12.3 ± 1.4 vs. 13.6 ± 1.4 g/dl), serum iron (61.4 ± 18.3 vs. 93.7 ± 33.7 mcg/dl), transferrin iron binding capacity (20.7 ± 8.4 vs. 31.1 ± 15.6 %), and e-GFR values (78.1 ± 36.1 vs. 118.1 ± 33.9 ml/min/1.73 m2) in comparison to patients with preserved ejection fraction, while unsaturated iron binding capacity (272.6 ± 74.9 vs. 221.7 ± 61.4 mcg/dl), hepcidin (4.61 ± 0.89 vs. 3.28 ± 0.69 ng/ml), and creatinine (1.34 ± 0.55 vs. 1.03 ± 0.25 mg/dl) were significantly higher in the same group. When considering inflammatory parameters, patients with reduced ejection fraction showed significantly higher expression of both Toll-like receptors-2 (1.90 ± 0.97 vs. 1.25 ± 0.76 MFI) and Toll-like receptors-4 (4.54 ± 1.32 vs. 3.38 ± 1.62 MFI), respectively, as well as a significantly higher activity of NF-κB (2.67 ± 0.60 vs. 1.07 ± 0.30). Furthermore, pro-inflammatory cytokines, interleukin-1, and interleukin-6, was significantly higher in patients with reduced ejection fraction, while the protective cytokine interleukin-10 was significantly lower in the same group. Correlational analyses demonstrated a significant and inverse relationship between left ventricular function and inflammatory parameters in patients with reduced ejection fraction, as well as a direct correlation between ferritin and inflammatory parameters. Conclusions: Our data demonstrate a different immune-mediated inflammatory burden in heart failure patients with reduced or preserved ejection fraction, as well as significant differences in iron status. These data contribute to further elucidate pathophysiologic mechanisms leading to cardiac dysfunction
    corecore