Highly Deformable Porous Electromagnetic Wave Absorber Based on Ethylene-Propylene-Diene Monomer/Multiwall Carbon Nanotube Nanocomposites

The need for electromagnetic interference (EMI) shields has risen over the years as the result of our digitally and highly connected lifestyle. This work reports on the development of one such shield based on vulcanized rubber foams. Nanocomposites of ethylene-propylene-diene monomer (EPDM) rubber and multiwall carbon nanotubes (MWCNTs) were prepared via hot compression molding using a chemical blowing agent as foaming agent. MWCNTs accelerated the cure and led to high shear-thinning behavior, indicative of the formation of a 3D interconnected physical network. Foamed nanocomposites exhibited lower electrical percolation threshold than their solid counterparts. Above percolation, foamed nanocomposites displayed EMI absorption values of 28-45 dB in the frequency range of the X-band. The total EMI shielding efficiency of the foams was insignificantly affected by repeated bending with high recovery behavior. Our results highlight the potential of cross-linked EPDM/MWCNT foams as a lightweight EM wave absorber with high flexibility and deformability

Electrical aging of 15 kV EPR cables energized by ac voltage with switching impulses superimposed

In this study, the electrical aging of 15 kV Ethylene Propylene Rubber (EPR) power cables, located in PVC pipes containing water, was conducted by ac voltage with switching impulses superimposed. The experiments provided a better understanding of the electrical aging phenomenon of EPR cable insulation. They also helped to assess the reliability of EPR cables used under such circumstances. EPR cable insulation was aged by rated ac voltage with switching impulses superimposed. The experiments also examined the degradation of EPR insulation by elevated ac voltage with switching impulses superimposed. Partial discharge parameters, capacitance and dissipation factor were measured at subsequent intervals during the aging process so as to understand the factors affecting aging process. After completion of the aging study, the remaining dielectric strength of tested cables was evaluated by ac breakdown voltage measurement

Dielectric Performance of Silica-Filled Nanocomposites Based on Miscible (PP/PP-HI) and Immiscible (PP/EOC) Polymer Blends

open14siThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 720858This study compares different polymer-nanofiller blends concerning their suitability for application as insulating thermoplastic composites for High Voltage Direct Current (HVDC) cable application. Two polymer blends, PP/EOC (polypropylene/ethylene-octene copolymer) and PP/PP-HI (polypropylene/ propylene - ethylene copolymer) and their nanocomposites filled with 2 wt.% of fumed silica modified with 3-aminopropyltriethoxysilane were studied. Morphology, thermal stability, crystallization behavior dynamic relaxation, conductivity, charge trap distribution and space charge behavior were studied respectively. The results showed that the comprehensive performance of the PP/PP-HI composite is better than the one of the PP/EOC composite due to better polymer miscibility and flexibility, as well as lower charging current density and space charge accumulation. Nanosilica addition improves the thermal stability and dielectric properties of both polymer blends. The filler acts as nucleating agent increasing the crystallization temperature, but decreasing the degree of crystallinity. Dynamic mechanical analysis results revealed three polymer relaxation transitions: PP glass transition ( eta ), weak crystal reorientation ( alpha 1 ) and melting ( alpha 2 ). The nanosilica introduced deep traps in the polymer blends and suppressed space charge accumulation, but slightly increased the conductivity. A hypothesis for the correlation of charge trap distribution and polymer chain transition peaks is developed: In unfilled PP/EOC and PP/PP-HI matrices, charges are mostly located at the crystalline-amorphous interface, whereas in the filled PP/EOC/silica and PP/PP-HI /silica composites, charges are mostly located at the nanosilica-polymer interface. Overall, the PP/PP-HI (55/45) nanocomposite with 2 wt.% modified silica and 0.3 wt.% of antioxidants making it a promising material for PP based HVDC cable insulation application with a reduced space charge accumulation and good mechanical properties.openHe X.; Seri P.; Rytoluoto I.; Anyszka R.; Mahtabani A.; Naderiallaf H.; Niittymaki M.; Saarimaki E.; Mazel C.; Perego G.; Lahti K.; Paajanen M.; Dierkes W.; Blume A.He X.; Seri P.; Rytoluoto I.; Anyszka R.; Mahtabani A.; Naderiallaf H.; Niittymaki M.; Saarimaki E.; Mazel C.; Perego G.; Lahti K.; Paajanen M.; Dierkes W.; Blume A

Breakdown properties of high density polyethylene and polypropylene blends

In high voltage (HV) applications, thermoplastic polymers are preferred to be used as insulators especially in cable technology. Polyethylene (PE) and polypropylene (PP) have been widely used due to their advantages of having good mechanical strength, thermal properties and electrical properties. However, there are weaknesses for each type of polymer (either PE or PP) that can be improved. Degradations and failures of insulators may cause a big impact to high voltage equipment when flashover occurred, thus damaging the equipment. The use of polymer blends may compensate the weaknesses of each polymer. In this paper, thermoplastic polymer blends composed of high density polyethylene (HDPE) and polypropylene (PP) homopolymer were formulated through melt blending method. The breakdown properties of the polymer blends with different compositions were investigated and analysed. Five samples of polymers composed of 100% HDPE, 80% HDPE and 20% PP, 50% HDPE and 50% PP, 20% HDPE and 80% PP, and 100% PP were chosen for investigation purposes. The breakdown results obtained were analysed using Weibull software. The results showed that thermoplastic blends revealed good breakdown performance. These improvements can be transformed into favourable choices and cost effective solutions in electrical power systems

VISCOELASTIC RELAXATION CHARACTERISTICS OF RUBBERY POLYMER NETWORKS AND ENGINEERING POLYESTERS

The relaxation characteristics of rubbery poly(ethylene oxide) [PEO] networks have been investigated as a function of network composition and architecture via dynamic mechanical analysis and broadband dielectric spectroscopy. A series of model networks were prepared via UV photopolymerization using poly(ethylene glycol) diacrylate [PEGDA] as crosslinker: variations in crosslink density were achieved either by the introduction of water in the prepolymerization reaction mixture, or by the inclusion of mono-functional acrylate such as poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA]. Copolymerization with mono-functional acrylate led to the insertion of flexible branches along the network backbone, and the corresponding glass-rubber relaxation properties of the copolymers (i.e., Tg, relaxation breadth, fragility) were a sensitive function of network architecture and corresponding fractional free volume. Relatively subtle variations in network structure led to significant differences in relaxation characteristics, and a systematic series of studies was undertaken to examine the influence of branch length, branch end-group, and crosslinker flexibility on viscoelastic response. Dielectric spectroscopy was especially useful for the elucidation of localized, sub-glass relaxations in the polymer networks: the imposition of local constraint in the vicinity of the crosslink junctions led to the detection of a distinctive fast relaxation process in the networks that was similar to a comparable sub-glass relaxation observed in crystalline PEO and in the confined regions of PEO nanocomposites. Gas permeation studies on the model PEGDA networks confirmed their utility as highly-permeable, reverse-selective membrane materials, and strategic control of the network architecture could be used to optimize gas separation performance. Dynamic mechanical and dielectric measurements have also been performed on a semicrystalline polyester, poly(trimethylene terephthalate) [PTT], in order to assess the influence of processing history on the resultant morphology and corresponding viscoelastic relaxation characteristics. Studies on both quenched and annealed PTT revealed the presence of a substantial fraction of rigid amorphous phase (RAP) material in the crystalline samples: dielectric measurements showed a strong increase in relaxation intensity above the glass transition indicating a progressive mobilization of the rigid amorphous phase with increasing temperature prior to crystalline melting

Polymer nanodielectrics and sensors for capacitor and cable applications

Capacitive polymer-matrix composites (PMCs) were fabricated with various nanofillers, defined as nanodielectrics. Surface modification of nanofillers was conducted to improve the homogeneity of nanocomposites. A capacitive sensor was designed and fabricated to measure dielectric properties of thermally aged cable jackets for the purpose of nuclear power plant (NPP) cable status monitoring. Silanized-Si/epoxy nanocomposites were studied for structural capacitors. The surface treatment of Si nanoparticles by silane coupling agents was achieved to improve dispersion of nanofillers in an epoxy matrix. The nanocomposite shows an increase of dielectric breakdown strength and dielectric constant with no significant increase in loss tangent at 10 wt.% silanized-Si loading. Furthermore, the introduction of silanized nano-Si increases the storage modulus of epoxy and the Tg shows good thermal stability. The silianized Si/epoxy nanocomposite is a promising material for future structural capacitors. Dielectric properties of silanized-Si/epoxy nanocomposites were investigated for a comprehensive understanding of the nanodielectric system. Dielectric spectra of nanocomposites were fitted by Havriliak-Negami (HN) dielectric relaxation functions with a power-law conduction term. Maxwell-Wagner-Sillars (MWS) interfacial polarization relaxation was observed in silanized-Si/epoxy nanocomposites. Further, Weibull distribution analysis was applied to study the dielectric breakdown behaviors. Silanized Si/epoxy exhibits high dielectric breakdown strength and a narrow distribution of failure points. Dielectric properties of another nanodielectric system, poly(methyl methacrylate) (PMMA)/montmorillonite (MMT), were investigated to study the effect of MMT and the interface to the polymer. The data was analyzed with a sum of HN functions and a power-law conduction term. As MMT content increases, an MWS relaxation emerges in the nanocomposites and α-relaxation is contributed by main-chain movements above T¬g. The characteristic frequency of β-relaxations is influenced by the mergence with the α-relaxation above T¬g. A capacitive sensor was created for monitoring NPP cable jacket degradation. Ethylene propylene rubber (EPR) and cross-linked polyolefin (XLPO) cable jackets were studied in this research. Accelerated thermal aging was conducted on cable jackets. The decrease of capacitance against aging time measured on XLPO correlates well with observed changes in elongation-at-break. Capacitance of aged EPR, however, did not show a strong correlation with observed EAB for the samples studied here

A Review of Polypropylene and Polypropylene/Inorganic Nanocomposites for HVDC Cable Insulation

Due to its excellent electrical and thermal performance, as well as satisfying the needs for developing the environmentally friendly and recyclable cable insulation material, polypropylene has caused widespread concern. Nanodoping can effectively improve the electrical, thermal and mechanical properties of polypropylene nanocomposites, which provides a new method to solve the problems in its application in HVDC cable insulation. This chapter introduces research achievements on polypropylene and polypropylene/inorganic nanocomposites, which states the effects of nanodoping on the electrical properties, such as space charge behaviors, electrical tree aging, breakdown strength, etc. thermal conductivity and mechanical properties of the polypropylene and its multi-blends. The aging mechanism under different conditions is also discussed. The analysis shows that the surface treatment of nanoparticles can reduce the aggregation of nanoparticles and strengthen the interface effect, thus improving the comprehensive properties of polypropylene nanocomposites. This chapter also summarized the feasibility and future development of the polypropylene and its nanocomposites application in the insulation of HVDC cables

Dielectric mixtures -- electrical properties and modeling

In this paper, a review on dielectric mixtures and the importance of the numerical simulations of dielectric mixtures are presented. It stresses on the interfacial polarization observed in mixtures. It is shown that this polarization can yield different dielectric responses depending on the properties of the constituents and their concentrations. Open question on the subject are also introduced.Comment: 40 pages 12 figures, to be appear in IEEE Trans. on Dielectric

Space charge and dielectric response measurements to assess insulation aging of low-voltage cables used in nuclear power plants

The current design life of nuclear power plant (NPP) could potentially be extended to 80 years. During this extended plant life, all safety and operationally relevant Instrumentation & Control (I&C) systems are required to meet their designed performance requirements to ensure safe and reliable operation of the NPP, both during normal operation and subsequent to design base events. This in turn requires an adequate and documented qualification and aging management program. It is known that electrical insulation of I&C cables used in safety related circuits can degrade during their life, due to the aging effect of environmental stresses, such as temperature, radiation, vibration, etc., particularly if located in the containment area of the NPP. Thus several condition monitoring techniques are required to assess the state of the insulation. Such techniques can be used to establish a residual lifetime, based on the relationship between condition indicators and ageing stresses, hence, to support a preventive and effective maintenance program. The object of this thesis is to investigate potential electrical aging indicators (diagnostic markers) testing various I&C cable insulations subjected to an accelerated multi-stress (thermal and radiation) aging