Mathematical modeling is a fundamental instrument in the development of theoretical validation for experimental results and in their interpretation. The gist of this article is the application of a special multivalued function, called Lambert W function, to several aspects of electrical engineering. This multivalued function serves the purpose of inverting a vast gamut of expressions involving exponential functions and can be used in many models concerning electrical insulation issues, yielding lower computational times as opposed to other methods to solve nonlinear problems. In particular, this article presents the analytical calculation of parameters for capacitor field and equipotential lines, Paschen's law inversion, a model for electric field distribution in power cables, the inversion of Schottky and Dissado, Montanari, and Mazzanti model for cable life estimation.

This paper deals with the investigation of the insulating properties of EPDM materials subjected to radiation aging with two non-destructive techniques: electrical (dielectric spectroscopy) and chemical (FTIR). Flat samples of EPDM were subjected to accelerated aging at 860 Gy/h for 664 h with four withdrawals at room temperature. The dielectric spectroscopy results indicate that the tan delta at 100 kHz coherently follows the aging evolution of the materials and it is suggested to be a suitable aging marker. The spectra of FTIR results suggest that EPDM undergoes chain scission and oxidation after radiation ageing. These results confirm the suitability of the electrical nondestructive technique for aging evaluation.

This study investigates the electrical behavior of Ethylene Propylene Rubber (EPR) insulation used in instrumentation and control (I&C) cables in nuclear power plants (NPPs). Cables were subjected to different accelerated radiation aging dose rates, 100 Gy/h and 800 Gy/h respectively. After aging, dissipation factor (tan delta) trend with frequency from 500 Hz to 500 kHz was obtained. Results show that tand of the higher dose rates depicts a faster increase than the lower one, following the aging severity. In particular, the tand trend at high frequencies (greater than 100 kHz) shows a linear increase with aging for both dose rates, proposing it as a suitable radiation aging marker for EPR materials.

This paper presents a comprehensive study on the impact of antioxidants (AOs) on the aging process of insulating polymeric materials, specifically complex permittivity, conductivity, and AC breakdown voltage. Accelerated aging was achieved through high temperatures (up to 130°C) in air on crosslinked polyethylene (XLPE) both with and without AOs. In addition to electrical tests, chemical analyses were performed to better understand the role of AOs during thermal aging. The results indicate that AOs effectively inhibit oxidation, preventing the formation of degradation species. As long as AOs are present, minimal changes in the electrical properties are observed. However, once the AOs are almost completely depleted, oxidation products significantly alter the electrical properties, resulting in a worsening of the material electrical performance.

This article discusses the effects of thermal stress on polyethylene terephthalate (PET) films focusing on its impact on the capability of the insulation to withstand voltage waveforms with an elevated frequency content. To properly mimic the degradation the material may face during its service life, thin (∼50 μm) PET films were subjected to accelerated thermal aging at 150, 165 and 180 °C. Aging effects (including oxidation) on the chemical structure of PET were investigated by means of Fourier Transform InfraRed spectroscopy. Dielectric spectroscopy was performed on samples to evaluate the dielectric losses at the different aging stages. To simulate the worst-case scenario during operation, high frequencies (up to 30 kHz) were selected and used for the AC breakdown tests, thus assessing the evolution of the PET dielectric strength with aging. Results showed that no direct correspondence between dielectric strength and dissipation factor (tanδ) values is present, suggesting that thermal runaway is not the only factor causing the dielectric breakdown.

This work deals with the space charge investigation of nanostructured epoxy resin (Sigma Aldrich DER332) filled with Carbon Quantum Dots. Space charge characteristics of the material are obtained by investigating the characteristic curves coming from Thermally Stimulated Depolarization Current measurement. In particular, the analysis of these curves highlights the occurrence of a significant shift in glass transition temperature in the nanocomposite. Furthermore, the incorporation of Carbon Quantum Dots is confirmed by an increase in the inertia in the first step of the performed measurement and by the presence of a Maxwell-Wagner-Sillars peak in the plot of the discharging current. Nonetheless, activation energies of the relaxation processes appearing in TSDC plots do not experience any detectable variation, thus suggesting that the chemical structure of the nanocomposite retains some characteristics of the neat epoxy resin.

This paper presents the preliminary characterization of EPDM insulation systems used for nuclear power cables. Electrical characterization is achieved by means of high voltage dielectric spectroscopy and pulsed electroacoustic (PEA) methods for space charge measurements in order to evaluate both the AC and DC performance of the considered materials. Results show that the increase of the applied electric field does not significantly impact the real part of permittivity, while it leads to the reduction of the dielectric losses at power frequency. On the other hand, PEA measurements claim that little quantity of positive charges are injected and trapped inside the material.

This paper focuses on the effect of high dose radiation on the electric insulation of superconducting wires used in particle accelerator magnets. The analysis focuses on the evolution of the electrical properties, due to radiation doses, of the poly-vinyl acetate (PVA) insulation of these wires, particularly complex permittivity. This aims at verifying the suitability of the dielectric spectroscopy technique as a nondestructive approach for the aging assessment of these wires, usually placed in inaccessible areas. This is achieved by comparing results coming from complex permittivity with oxidation buildup obtained through Fourier Transform Infra-Red (FTIR) spectroscopy.

This article investigates the evolution of electrical properties of polyethylene terephthalate (PET) with thermal aging. Electrical tests are performed within a wide range of frequencies in order to simulate the application conditions of insulating materials in inverter-fed machines. In particular, for the aging conditions considered, the real part of permittivity showed to be correlated with the concentration of the degradation species, investigated through FTIR. On the contrary, the dielectric breakdown at high frequencies showed to be independent from the corresponding values of the dissipation factor (tanδ). This behavior would imply that thermal runaway is not the principal phenomenon leading to the dielectric failure.

In this article, the electrical characterization of nanostructured polyimide (PI) films is presented. The addition of silicon nitride $({\mathrm{S}{\mathrm{i}}_3\ {\mathrm{N}}_4})$ as nanoparticles ensures an enhanced thermal conductivity and high temperature endurance of PIs, without worsening their electrical performances. The effect of different concentrations of nanoparticles on the base PI is investigated by means of broadband dielectric spectroscopy and thermally stimulated depolarization currents (TSDC).

In this article, the impact of two different antioxidants (Irganox®1076 and PS802) on the electrical properties of a cross-linked polyethylene (XLPE) matrix is investigated and discussed. Materials were tested by means of dielectric spectroscopy, thermally stimulated depolarization currents (TSDC) and DC conductivity measurements to provide a comprehensive analysis for their applications under AC and DC electric fields. Results reveal that electrical properties are notably modified by the introduction of additives and the amplitude of variation is somehow proportional to the concentration of the additive with respect to the polymer matrix. In particular, TSDC measurements claim that antioxidants introduce deep traps (>1 eV) inside the base material and the density of these traps increases in accordance with antioxidant concentration. Moreover, due to the polar properties of these species, the complex permittivity raises with respect to base XLPE, and it adequately follows the antioxidant concentration. On the contrary, negligible variations in terms of DC conductivity are recorded.

This study focuses on the preparation of nanocomposite polymer separators by the electrospinning technique. PVDF-HFP polymer was combined with different concentrations of ZrO2 (0, 5, 7, and 10 wt%). The fabricated nanofibrous mats were analyzed to evaluate their electrochemical and mechanical properties. The incorporation of the ceramic filler was investigated to determine its influence on the separator performance, aiming to develop high-performance separators for future Energy Storage Systems (ESSs).

This work presents an innovative model for the derivation of permittivity evolution of polyethylene (PE)-based materials with aging. First, the derivation of the microscale contributions to the real permittivity of methylene unit [constitutive repetitive unit (CRU) of PE] and its oxidation products, that is, ketones and hydroperoxides, in the solid state is presented. Then, a chemical kinetic model is recalled predicting the concentration, under proper hypotheses, of the oxidized species created during polymer aging. The proposed model combines the concentrations of methylene unit and its oxidation products with the respective contribution to permittivity, providing the trend of permittivity of polymer with aging. Results depict good agreement with the experimental data, validating the model.

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.

This work proposes an alternative method to address the correct calibration procedure of Pulsed Electro-Acoustic measurements, which minimizes the possibility of an incorrect evaluation regarding space charge accumulation at the very beginning of polarization in a material. This is done by monitoring the potential of a floating mass in the thickness of the material to be tested. Results show that the proposed method is a viable option, with much less uncertainties than more traditional methods.

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.

The evolution of properties of crosslinked polyethylene (XLPE)-based insulating materials under radio-chemical ageing conditions is presented and discussed. In total, seven different polymer compounds were tested, characterised by an increasing quantity of additives, for example, antioxidants (AOs) and fillers as flame retardants. Samples were analysed using different testing techniques, that is, Fourier Transform Infra-Red and dielectric spectroscopy. This allowed a broad characterisation of the polymer, bringing to good correlations between the arising of new chemical groups caused by ageing and the modifications on the complex permittivity. Phenol-based AOs are found to be the most efficient in terms of protection against oxidation. On the contrary, flame retardants are concluded not to have any impact on the material ageing. Acquired data were then treated using the principal component analysis. The data treatment successfully distinguished the material composition (with and without additives) and the ageing environments. The results confirm the relevance of this analysis in understanding the impact of irradiation on the chemical and functional properties of the polymer materials studied.

This work presents the development, validation, and sensitivity analyses of a portable device capable of performing high-frequency dielectric spectroscopy tests on site. After a brief introduction on the operation principle and the description of the impact of frequency on dielectric spectroscopy, the article presents the results of tests on reference samples confirming good agreement with expected values. The frequency region in which the device operates, 1–200 kHz, was chosen because of its correlation with oxidative species of polymeric compound. The sensitivity analyses were performed measuring the dielectric response of low voltage cables with different aged lengths. The outcome of these tests is twofold. On the one hand, they confirm the suitability of the technique for aging evaluation, and, on the other hand, they allow the assessment of the minimum aged length (damage ratio) which causes appreciable variations on the obtained dielectric spectrum. This quantity was found to be ~35% of the total cable length.

In this article the incorporation of core CdSe and coreshell CdSe-ZnS Quantum Dots in an epoxy resin is studied. In particular, TSDC and PEA measurements were performed in order to understand whether the nanofillers had an impact on the electrical behavior of the resin. The results show that Quantum Dots influence space charge behavior, introducing traps which are significantly deeper than the pure resin ones. Moreover, space charge injection phenomena seem to be reduced by the presence of nanoadditives.

Characterization of traps in dielectrics is very important to properly describe their space charge behavior. An alternative technique to standard Isothermal Surface Potential Decay measurements is proposed in this paper. The proposed method allows for estimation of potentials both during the polarization phase and immediately after depolarization of surfaces, monitoring of fast surface potential transients as well as slower ones. Results from both evaluations and space charge depolarization measurements on samples of DER332 epoxy resin are in good agreement with each other, showing that there are two predominant traps at energies of 0.81 eV and 0.92 eV respectively and validating the proposed innovative procedure.