Jens Rocks

Due to their excellent electrical insulation properties and processability, polymer materials are used in many electrical products. It is widely believed that space charge plays an important role for the electric field distribution, conduction, ageing, and electric breakdown of polymeric insulation. This paper reviews measurements and characteristics of space charge behavior which mainly determined by the pulsed electro-acoustic (PEA) measurement technique. Particular interests are the effects… Mehr anzeigen

Due to their excellent electrical insulation properties and processability, polymer materials are used in many electrical products. It is widely believed that space charge plays an important role for the electric field distribution, conduction, ageing, and electric breakdown of polymeric insulation. This paper reviews measurements and characteristics of space charge behavior which mainly determined by the pulsed electro-acoustic (PEA) measurement technique. Particular interests are the effects of the applied voltage, the electrodes, temperature, humidity, microstructure, additives, and filler materials on accumulation, distribution, transport, and the decay of space charge in polymeric materials. This review paper is to provide an overview on various space charge effects under different conditions, and also to summarize the information for polymeric materials with suppressed space charge and improved electrical behavior. Weniger anzeigen

This paper attempts to study the relationship between the various properties and different composition of the Polyhedral Oligomeric Silsesquioxanes (POSS) mixture hybrid epoxy composites, and two kinds of low cost POSS mixtures containing diversified structure have been synthesized by polycondensation method, which could be applied as potential alternatives of expensive commercialized POSS. Lower permittivity can be obtained by incorporating POSS mixture, but permittivity value did not follow… Mehr anzeigen

This paper attempts to study the relationship between the various properties and different composition of the Polyhedral Oligomeric Silsesquioxanes (POSS) mixture hybrid epoxy composites, and two kinds of low cost POSS mixtures containing diversified structure have been synthesized by polycondensation method, which could be applied as potential alternatives of expensive commercialized POSS. Lower permittivity can be obtained by incorporating POSS mixture, but permittivity value did not follow the change of content of POSS mixture. The improved AC breakdown strength was achieved with adding 5 wt% POSS mixture. Thermal properties were tested using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA), glass transition temperature of composites were increased with addition of 5 wt% POSS mixture and then decreased with higher content, while thermo-oxidation resistance of composites has significantly improved with increasing content of POSS mixture. Besides, the tensile strength of composites has no obvious change by incorporating POSS mixture in the epoxy resins, and the morphology of composites analyzed by scanning electron microscope-energy dispersive X-Ray spectroscopy (SEM-EDS) revealed the similar fracture mode of neat epoxy resin and composites and showed good compatibility between POSS mixture and epoxy. Weniger anzeigen

This paper attempts to study the relationship between the various properties and different composition of the Polyhedral Oligomeric Silsesquioxanes (POSS) mixture hybrid epoxy composites, and two kinds of low cost POSS mixtures containing diversified structure have been synthesized by polycondensation method, which could be applied as potential alternatives of expensive commercialized POSS. Lower permittivity can be obtained by incorporating POSS mixture, but permittivity value did not follow… Mehr anzeigen

This paper attempts to study the relationship between the various properties and different composition of the Polyhedral Oligomeric Silsesquioxanes (POSS) mixture hybrid epoxy composites, and two kinds of low cost POSS mixtures containing diversified structure have been synthesized by polycondensation method, which could be applied as potential alternatives of expensive commercialized POSS. Lower permittivity can be obtained by incorporating POSS mixture, but permittivity value did not follow the change of content of POSS mixture. The improved AC breakdown strength was achieved with adding 5 wt% POSS mixture. Thermal properties were tested using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA), glass transition temperature of composites were increased with addition of 5 wt% POSS mixture and then decreased with higher content, while thermo-oxidation resistance of composites has significantly improved with increasing content of POSS mixture. Besides, the tensile strength of composites has no obvious change by incorporating POSS mixture in the epoxy resins, and the morphology of composites analyzed by scanning electron microscope-energy dispersive X-Ray spectroscopy (SEM-EDS) revealed the similar fracture mode of neat epoxy resin and composites and showed good compatibility between POSS mixture and epoxy. Weniger anzeigen

Bi-axially oriented PEN film has superior performance in terms of dielectric strength, mechanical strength, heat resistance, anti-hydrolysis, etc. Thus, it has been widely used for energy storage applications, such as capacitors and batteries. In this paper, we attempted to increase the dielectric strength of PEN films by electron beam irradiation. PEN films of two different thickness, 6 µm and 12 µm, were exposed to an electron beam of 10 MeV energy. Improvement of breakdown strength was… Mehr anzeigen

Bi-axially oriented PEN film has superior performance in terms of dielectric strength, mechanical strength, heat resistance, anti-hydrolysis, etc. Thus, it has been widely used for energy storage applications, such as capacitors and batteries. In this paper, we attempted to increase the dielectric strength of PEN films by electron beam irradiation. PEN films of two different thickness, 6 µm and 12 µm, were exposed to an electron beam of 10 MeV energy. Improvement of breakdown strength was observed for both 6 µm and 12 µm PEN films. The largest increase was 13% for 12 µm PEN films with dosage of 100 kGy. The distribution of breakdown test results also improved upon irradiation as the increase of the shape parameter of Weilbull distribution. Post heat treatment slightly increased the dielectric strength for 12 µm but decreased the shape parameter of the breakdown test results for 6 µm. Weniger anzeigen

Hydrophobic cycloaliphatic epoxy (HCEP) has been used as outdoor insulation material to maintain good electrical performances under multiple stresses, in which acidic attack to this kind of materials has been causing concern in recent years. To study the performances of HCEPs under acid rain, a new acid fog test method has been established and an acid fog chamber was constructed. During the 1000 h acidic rain test, contact angles of the HCEPs decreased and the less hydrophobic samples had… Mehr anzeigen

Hydrophobic cycloaliphatic epoxy (HCEP) has been used as outdoor insulation material to maintain good electrical performances under multiple stresses, in which acidic attack to this kind of materials has been causing concern in recent years. To study the performances of HCEPs under acid rain, a new acid fog test method has been established and an acid fog chamber was constructed. During the 1000 h acidic rain test, contact angles of the HCEPs decreased and the less hydrophobic samples had higher leakage currents. Increase of the surface roughness and diameters of the micro holes have been observed by AFM and SEM, and oxidation of surface groups was analyzed by FTIR. Resistance to tracking and erosion remained good after the 1000 h test. The results showed that HCEPs exhibited good outdoor insulation performances in acidic fog under DC stress. Weniger anzeigen

The main goal of the study is to explore epoxy composites with a low permittivity and acceptable other properties, especially mechanical properties and dielectric strength, for electric power applications. The influence of filler surface treatment and filler content on mechanical, thermal and dielectric properties of epoxy composites was systematically investigated. Epoxy composites were prepared with both silanized and non-silanized glass bubbles. The different filler treating methods had a… Mehr anzeigen

The main goal of the study is to explore epoxy composites with a low permittivity and acceptable other properties, especially mechanical properties and dielectric strength, for electric power applications. The influence of filler surface treatment and filler content on mechanical, thermal and dielectric properties of epoxy composites was systematically investigated. Epoxy composites were prepared with both silanized and non-silanized glass bubbles. The different filler treating methods had a significant effect on mechanical properties and only a minor effect on thermal properties and dielectric permittivity. The filler content has an important influence on epoxy composites preparation and mechanical and dielectric properties. With the increasing glass bubble content up to 35 wt.% (52.4 vol.%), the following results were obtained: 1) the mechanical properties decreased with the filler content, while the specific strength and modulus increased or remained the same; 2) the permittivity decreased with the filler content; 3) the dielectric strength was similar to that of the unfilled epoxy resin, while compared with high loading silica flour filled epoxy composites, there is an obvious dielectric strength decrease. This could limit the application of glass bubble filled epoxy material in specific cases. Further research is required to improve the dielectric strength of the material.

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Gas-to-air and gas-to-oil bushings are vital components of SF6 gas insulated switchgear (GIS) systems, connecting GIS to a transformer or to an overhead line. Capacitively graded, resin-impregnated-paper (RIP) bushings are the state-of-the art solution for both applications, offering the smoothest distribution of the radial and axial electric field while using the dry, solid-state, environmentally friendly insulating material.

In this work the results of electrical and environmental testing of outdoor silicone rubber insulating materials are presented. Degradation paths in silicone insulation were occasionally observed in the artificially accelerated and field tests. Chemical analysis of material in the degradation path has shown that the original material had transformed into the orthorhombic mullite Al6Si2O13. The formation of mullite in the degradation paths indicates that local surface temperatures during… Mehr anzeigen

In this work the results of electrical and environmental testing of outdoor silicone rubber insulating materials are presented. Degradation paths in silicone insulation were occasionally observed in the artificially accelerated and field tests. Chemical analysis of material in the degradation path has shown that the original material had transformed into the orthorhombic mullite Al6Si2O13. The formation of mullite in the degradation paths indicates that local surface temperatures during discharge activity on the surface may well be over 1200degC degrees. Alumina trihydrate (ATH) filler was observed to be homogeneously distributed in the studied material. The filler had platelet-like form and was hexagonal in shape. The filler particles were several micrometers in size with submicrometer thickness. In addition to the ATH filler, occasional impurities such as NaCl and KCl salt crystals were observed in the bulk material. Soxhlet extraction has shown that tested high temperature vulcanised rubbers (HTV) contained about 2%w of low molecular weight (LMW) silicone species while liquid silicone rubber (LSR) contained about 4%w of LMW silicone Weniger anzeigen

The thermal curing behavior of tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and a co-anhydride mixture consisting of maleic anhydride (MA) and hexahydrophthalic anhydride (HHPA) was studied from 55 to 100 °C by real-time FT-Raman spectroscopy. The quantitative changes in concentrations of anhydride, epoxy, and new-formed ester were measured and empirical reaction rate curves were constructed reflecting the kinetics of the curing process. After an induction period a simple kinetic scheme… Mehr anzeigen

The thermal curing behavior of tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and a co-anhydride mixture consisting of maleic anhydride (MA) and hexahydrophthalic anhydride (HHPA) was studied from 55 to 100 °C by real-time FT-Raman spectroscopy. The quantitative changes in concentrations of anhydride, epoxy, and new-formed ester were measured and empirical reaction rate curves were constructed reflecting the kinetics of the curing process. After an induction period a simple kinetic scheme that is first order in both epoxy and anhydride monomer consumption described the reaction profile until the reaction was influenced by chemo-rheological changes due to vitrification transition.

FT-Raman analysis revealed that curing propagation mainly occurs by polyesterification between epoxide and anhydride. Possible side reactions including the homopolymerization of MA are considered. The main side reaction is decarboxylation of MA that may produces some autocatalysis, but this is a minor contribution to the kinetics of cure. No conclusive evidence has been found for homopolymerization of MA or initiation of the curing reaction by the reaction product of TGDDM and MA, compared to the polyesterification. Weniger anzeigen

Curing and gelation of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM, Araldite®MY721) in the presence of an anhydride hardener mixture were studied by calorimetric and dynamic rheological measurements. The cure kinetics of the homogeneous and low-temperature-curable epoxy system were evaluated from 40 to 140 °C, and the apparent activation energies of the curing reaction were calculated from different thermokinetic models. By comparison of different calorimetric and rheological… Mehr anzeigen

Curing and gelation of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM, Araldite®MY721) in the presence of an anhydride hardener mixture were studied by calorimetric and dynamic rheological measurements. The cure kinetics of the homogeneous and low-temperature-curable epoxy system were evaluated from 40 to 140 °C, and the apparent activation energies of the curing reaction were calculated from different thermokinetic models. By comparison of different calorimetric and rheological methods, it was found that the results from the isothermal calorimetric measurements are in good agreement with the results obtained from isothermal rheological experiments, while the kinetic parameter calculations based on dynamic calorimetric measurements are not reliable results. These differences mainly arise from the fact that dynamic measurements have many underlying assumptions and do not consider the equilibrium condition. Weniger anzeigen

The curing behaviour and thermomechanical properties of a technical grade of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM, Araldite®MY721), cured in the presence of an anhydride hardener mixture consisting of maleic anhydride (MA) and pyromellitic acid dianhydride (PMDA) was studied by calorimetric and dynamic mechanical analysis. The cure kinetics and the influence of varying stoichiometric anhydride-to-epoxy ratios were evaluated and the apparent activation energy was calculated… Mehr anzeigen

The curing behaviour and thermomechanical properties of a technical grade of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM, Araldite®MY721), cured in the presence of an anhydride hardener mixture consisting of maleic anhydride (MA) and pyromellitic acid dianhydride (PMDA) was studied by calorimetric and dynamic mechanical analysis. The cure kinetics and the influence of varying stoichiometric anhydride-to-epoxy ratios were evaluated and the apparent activation energy was calculated according to Barrett's method. High extents of conversion from DSC studies of the MY721-resin were reached after room temperature cure, without an added catalyst, for 24 h, followed by a post-curing step of 1 h at 90 °C. The ultimate glass transition temperatures for the molar anhydride/epoxy ratio, r = 0.8, were close to the decomposition temperature, and indications were obtained that the network structure consists of two independent sub-networks. It is suggested that two separate mechanisms contribute to the curing reaction at room temperature. First, the tertiary amine structure, intrinsic to aminoglycidyl resins, may act as an internal catalyst for the anhydride ring opening, and secondly, the unsaturated bond of MA participates in the curing reaction by nucleophilic attack, such as from tertiary amines or carboxylate or alkoxide anions. From a study of a range of different aminoglycidyl resins, this low-temperature curing behaviour is found to be a general phenomenon. Weniger anzeigen