This study investigates the combined influence of temperature and relative humidity on moisture sorption and electrical conduction in two reinforced PPS: PPS-A with 40 wt.% glass fibers and PPS-B with 65 wt.% glass fibers and mineral fillers. Moisture uptake measurements show a strong dependence on environmental conditions. When normalized to the polymer fraction, PPS-B exhibits a higher moisture content, whereas it has lower matrix content, highlighting the role of filler-matrix interfaces in water accumulation. Current density-electric field (J-E) measurements reveal thermally and moisture-activated conduction mechanisms. Under high humidity (80% RH), both materials exhibit a transition from ohmic conduction regime (slope $\approx 1)$ to a field-enhanced conduction regime with slopes between 2 and 2.6, consistent with space-charge-limited current. The transition occurs at lower electric fields in PPS-B ($\boldsymbol{\sim} \mathbf{1. 5 k V} / \mathbf{m m}$ at 50°C-80% RH) compared with PPS-A ($\approx \mathbf{6} \text{kV} / \text{mm}$ at $50^{\circ} \mathrm{C}-80 \%$ RH), indicating a stronger sensitivity to environmental conditions for PPS-B and effect of fillers on Eth. These results demonstrate that both hydrothermal conditions and composite microstructure strongly influence electrical conduction and must be considered in the design of PPS-based insulation for HVDC applications.

The electrification of aircraft requires insulating polymers capable of reliable operation under high-voltage DC stress. This study investigates the current-voltage behavior of glass-fiber-reinforced LCP and PEEK under controlled temperature and humidity. Results show that LCP exhibits mainly ohmic conduction at moderate temperature and only slight super-linear behavior at elevated temperature. In contrast, reinforced PEEK shows stronger field-dependent conduction, including humidityinduced transitions toward space-charge-limited current (SCLC) at $\mathbf{8 0}^{\circ} \mathbf{C}$ under 50%RH $\left(\mathbf{E}_{\text{Th }} \approx \mathbf{3 ~ k V} / \mathbf{m m}\right)$, and possible Schottky-type injection mechanisms at $\mathbf{5 0}^{\boldsymbol{\circ}} \mathbf{C}$. The results highlight the significant role of charge trapping and fiber-matrix interfaces in PEEK. These differences should be considered when selecting high-performance insulation materials for future HVDC aeronautical electrical systems.

The purpose of the presented study is to evaluate the lifetime of an insulating material for a high DC voltage in an airborne and an off-shore application. In order to accelerate the aging process, a thermal stress at 200°C was applied to coupons made of epoxy material (E). Some samples also undergo combined stresses. For a DC electric field of 3.8kV/mm, no dielectric breakdown was observed after 3 months of test, while for a field of 4.6kV/mm, breakdown of all coupons occurred in less than 30 hours. In order to understand aging mechanisms, several parameters were monitored during the tests. Space charge mapping, using the Pulsed Electro Acoustic (PEA) method, done at 150°C under 4.6kV/mm, showed that hetero-charges were trapped inside the material, leading to a local field enhancement in the material. For the applied field of 3.8kV/mm, the local electric field was below the critical threshold, and no breakdown was initiated. Dielectric spectroscopy was monitored during aging tests in the range of 10mHz-30Hz. A continuous increase of coupons impedance was observed during aging. The increase was even higher in the case of coupons which received the combined thermal and electrical stresses. Charge mapping with PEA showed that most of the charge relaxed after the voltage switch off. Hence it was concluded that the higher impedance increase during time with the cumulated stresses was probably not due to trapped charge inside the material. Instead, the applied DC stress had provoked an additional change of the material properties, compared to the thermal stress alone.

In aeronautics and in off-shore petroleum industries, the development of a DC (Direct Current) distribution at high voltage is necessary, in order to improve the systems operational performances, whether for aircrafts or pipe-lines for petroleum distribution. Such voltages may lead to phenomena of charge injection and accumulation in the electric systems insulation, also known as space charge. It can generate an electric field amplification, in the dielectric bulk or near the conductors, which in turn can trigger accelerated aging phenomena and premature failures. With the use of new materials, it is necessary to assess whether the space charge has a significant impact for the dielectrics of interest, and should be taken into account in the insulation sizing. This paper presents several ways to evaluate the phenomenon, and presents experimental results on Silicone, Epoxy and Fluoropolymers, in the range between 23°C and 200°C. As a perspective, the impact of space charge on the material aging is also discussed.

We here demonstrate the relevance of an electrooptic probe for the comprehensive and non invasive characterization of the electric field associated to partial discharge within aeronautic connectors. The proposed technique leads to the partial discharge detection thanks to a real time measurement of the field. The voltage threshold for discharges ignition has been evaluated. Finally, the precise localization of the discharges has been determined thanks to high resolution mapping of the field.

The purpose of this work is to study the behavior of airborne standard cables and connectors, when they are submitted to partial discharges. Experimental investigations are carried out: standard parts are placed at low pressure (100 mbars) and a squared bipolar high voltage of around 10kHz is applied, between 110% and 120% above the Partial Discharges Inception Voltage (PDIV). The partial discharges provoke an erosion of the insulation, and an electrical aging of the components. Breakdown is observed after a few hundreds of hours, depending on tested vectors. The PDIV is regularly recorded during the aging testing. Two different behaviors are observed: for the tested cable bundles, the PDIV decreases during the aging test, while for the tested connectors, surprisingly the PDIV increases during the test. In order to explain these phenomena, a numerical tool is used, by coupling an electrostatic solver to Paschen law and predict triggering of Townsend discharges. In the case of cables, a good correlation is obtained, with less than 20% of deviation between numerical and experimental results. In the case of connectors, the correlation is not straightforward and further investigations are in progress. In any case, these standard parts should not be used above the PDIV, and partial discharge free components need to be developed.

Partial Discharges affect insulating materials, especially when the operating voltage exceeds the nominal voltage for short periods. Hence, there is a need for improving the surface erosion resistance resulting from partial discharge. The present work aims to characterize the erosion (depth, shape) of PEEK samples, either unfilled, filled with mineral fillers or glass fibers. PD resistance was evaluated using a rod-to-plane electrodes test cell with an air gap of 0.2 mm. The thickness of the samples tested was 1 mm. The material sheets were subjected to PD under 50 Hz AC voltage from one to several weeks. After PD exposures, the erosion was characterized by analysis of the surface's roughness and erosion depth using a profilometer. EDX measurements also helped to evaluate the filler quantity on the surface of the specimen exposed to PD. The evolutions of erosion with time and as a function of applied voltage are presented. Comparisons are made on the effect of various filler contents. The possibility of enhancing PD resistance through proper selection of filler contents is discussed.

This paper defines an energy-based pulse reflection coefficient and a corresponding pulse matching ratio for the characterization of ultra-wide band antennas. As opposed to the usual frequency-domain reflection coefficient or VSWR, the proposed descriptors provide a relevant view on the amount of energy that is sent back to the transmitter. In order to evaluate the pulse reflection coefficient time-domain reflected voltage or time-domain reflection coefficient must be known. The definition of the pulse reflection coefficient is consistent with other definitions of energy-based time-domain descriptors such as the intercorrelation coefficient and the energy gain.

Cylindrical antennas are well-suited for military ultra-wide band (UWB) applications. In this article, we evaluate energy-based descriptors for three relevant types of cylindrical dipoles, including a novel stacked antenna. We show that the energy-based analysis provide a more realistic view on the transient radiation than the classical frequency-domain analysis. (c) 2008 Wiley Periodicals, Inc.

In this paper, we propose a novel original dual-band circularly polarized monolayer compact radiating structure. A method is described for switching from dual-band circularly polarized with opposite senses to dual-band circularly polarized in the same way.