Epoxy Insulation Research Articles

Study on the Estimation of Long Life Cycle and Reliability Tests for Epoxy Insulation Busway System

Study on the Estimation of Long Life Cycle and Reliability Tests for Epoxy Insulation Busway System

A Measurement Technique for Infrared Emissivity of Epoxy-Based Microwave Absorbing Materials.

Infrared (IR) emissivity is a critical parameter for modeling and predicting heat transfer by radiation. Microwave absorbing materials, having a high emissivity in the microwave spectrum, are crucial in a wide array of applications, such as electromagnetic interference mitigation, stealth technology, and microwave remote sensing and radiometer calibration. Accurate knowledge of the thermal properties of these materials is necessary for efficient design and optimization of these types of systems. Typical microwave absorbing materials consist of a dielectric epoxy material impregnated with a lossy material, such as iron or carbon. We study a novel cryogenically compatible epoxy-based absorber material that has been loaded with varying concentrations of carbonyl iron powder (CIP). We study six materials with CIP concentrations of 0%, 5%, 10%, 20%, 30%, and 50% by tap volume. We use a commercial IR camera with sensitivity in the range 7.5-13 μm to measure the radiance of the samples and a waterbath IR blackbody at ten temperatures between about 19 °C and 45 °C. A linear Deming fitting is performed, considering uncertainties in both the measured parameters, and the slope of the linear fit is shown to be the IR emissivity, averaged over the spectral response of the camera. The emissivity ranges between 0.868 and 0.757, decreasing monotonically as a function of iron carbonyl concentration between 0% and 50%. The uncertainty of the emissivity determination method is derived and presented. The uncertainty of the presented method is shown to be no larger than 3.3% for all measured samples.

Aminopropyltrimethoxysilane-functionalized boron nitride nanotube based epoxy nanocomposites with simultaneous high thermal conductivity and excellent electrical insulation

An ideal dielectric epoxy nanocomposite with high thermal conductivity is successfully fabricated utilizing aminopropyltrimethoxysilane-functionalized BNNTs.

Cryogenic electrical properties of irradiated cyanate ester/epoxy insulation for fusion magnets

The insulation materials used in high field fusion magnets require excellent mechanical properties, high electrical breakdown strength, good thermal conductivity and high radiation tolerance. Previous investigations showed that cyanate ester/epoxy (CE/EP) insulation material, a candidate insulation for fusion magnets, can maintain good mechanical performance at cryogenic temperature after 10 MGy irradiation and has a much longer pot life than traditional epoxy insulation material. In order to quantify the electrical properties of the CE/EP insulation material at low temperature, a cryogenic electrical property testing system cooled by a G-M cryocooler was developed for this study. An insulation material with 40% cyanate ester and 60% epoxy was subjected to 60Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min, and total doses of 1 MGy, 5 MGy and 10 MGy. The electrical breakdown strength of this CE/EP insulation material was measured before and after irradiation. The results show that cryogenic temperature has a positive effect on the electrical breakdown strength of this composite, while the influence of 60Co γ–ray irradiation is not obvious at 6.1 K.

Electrical performance of TGPAP and DGEBF-based epoxy resin insulation materials for superconducting magnets

For the insulation materials of the superconducting magnet, the mechanical and electrical properties should be guaranteed under stresses of cryogenic temperature and intense radiation. In this study, two types of epoxy resins were prepared, which consist of diglycidyl ether of bisphenol-F (DGEBF) and triglycidyl-p-aminophenol (TGPAP) as matrixes respectively, and diethyl toluene diamine (DETD), isopropylidenebisphenol bis[(2-glycidyloxy-3-n-butoxy)-1-propylether] (IPBE) and boron-free glass fibre were used as curing, toughing and reinforcing agents for each resin. The direct-current (dc) electric breakdown strength and flashover voltage, dielectric properties and space charge characteristics of both epoxy composites were investigated. According to the results, DGEBF composite shown a higher dielectric strength, lower permittivity and dielectric loss at cryogenic temperature and smaller shallow trap density, which makes it more potential to be used for the cryogenic insulation.

The insulating effect of the low thermal conductivity of epoxy on the resolution of the heat of reaction during polymerization by differential scanning calorimetry

It is demonstrated that the heat of epoxy cure as measured by isothermal differential scanning calorimetry (DSC), as commonly calibrated by the heat of fusion of an indium standard, is consistently low as compared to methods “directly” calibrated by Joule heating [i.e., isothermal microcalorimetry (IMC)]. The discrepancy between measurement techniques is shown to be on the order of 15% for low thermal conductivity epoxy thermosets. In addition to direct comparisons between DSC and IMC measurements during epoxy polymerization, indium samples embedded in cured epoxy were studied to determine if the DSC was able to accurately capture the total heat of fusion through the polymeric insulating layer. It is found that the indium heat of fusion measured by DSC is lower when the indium is embedded in epoxy than when the indium is in direct contact with a steel sample pan. The fraction of the indium heat of fusion detected through the epoxy insulation by the DSC cell is comparable to the fraction of the heat of reaction detected by DSC during epoxy cure, as determined from the DSC-IMC comparison. It is concluded that the heat flow detected by DSC during epoxy cure must be scaled by a factor of 1.18 in order to accurately portray the full heat of reaction under the conditions used in this work. It is argued that the difference found between DSC and IMC is in reasonable agreement with qualitative heat transfer calculations and with previous thermal conductivity measurement of polymers via DSC. The specific scaling factor is anticipated to depend on the material studied, on the pan type, on the sample geometry, on the purge gas details, and on the instrumentation. Instruments used in this work include a Q2000 DSC and a TAM Air IMC (both TA instruments). The epoxy was diglycidyl ether of bisphenol A (DGEBA) cured with diethanolamine (DEA).

Theoretical Study on Decomposition Mechanism of Insulating Epoxy Resin Cured by Anhydride.

High temperatures caused by partial discharge results in the decomposition of insulating epoxy resins in electrical equipment. In this paper, the ReaxFF force field is used to investigate the decomposition process of epoxy resins cured by anhydride and the formation mechanisms of small-molecule gases. Results show that the initiation reaction is the cleavage of an ester bond linked with an epoxy resin. Produced by the decomposition of ester groups, CO2 is the first and most abundant product. Meanwhile, CH2O can be generated through three main ways, although the process still depends on the decomposition of epoxy functional groups. H2O is produced by free radical collision and dehydration. The production of small-molecule gases has the following sequence: CO2, CH2O, CO, and H2O. The produced gases have the following order according to amount: CO2, CH2O, H2O, and CO.

Determination of Hydrophobic Contact Angle of Epoxy Resin Compound Silicon Rubber and Silica

Epoxy resin is a thermosetting polymeric material which is very good for application of high voltage outdoor insulator in electrical power system. This material has several advantages, i.e. high dielectric strength, light weight, high mechanical strength, easy to blend with additive, and easy maintenance if compared to that of porcelain and glass outdoor insulators which are commonly used. However, this material also has several disadvantages, i.e. hydrophilic property, very sensitive to aging and easily degraded when there is a flow of contaminants on its surface. The research towards improving the performance of epoxy resin insulation materials were carried out to obtain epoxy resin insulating material with high water repellent properties and high surface tracking to aging. In this work, insulating material was made at room temperature vulcanization, with material composition: Diglycidyl Ether Bisphenol A (DGEBA), Metaphenylene Diamine (MPDA) as hardener with stoichiometric value of unity, and nanosilica mixed with Silicon Rubber (SiR) with 10% (RTV21), 20% (RTV22), 30% (RTV23), 40% (RTV24) and 50% (RTV25) variation. The usage of nanosilica and Silicon Rubber (SIR) as filler was expected to provide hydrophobic properties and was able to increase the value of surface tracking of materials. The performance of the insulator observed were contact angle of hydrophobic surface materials. Tests carried out using Inclined Plane Tracking procedure according to IEC 60-587: 1984 with Ammonium Chloride (NH4Cl) as contaminants flowed using peristaltic pumps. The results show that hydrophobic contact angle can be determined from each sample, and RTV25 has maximum contact angle among others.

Improved DC flashover performance of epoxy insulators in SF6 gas by direct fluorination

In order to prove the effectiveness of direct fluorination in improving dc flashover performance of epoxy insulators in SF6 gas and also to provide evidence for the importance of surface conductivity of solid insulators, sheet-shaped and truncated cone epoxy samples were prepared and were fluorinated in a laboratory stainless vessel using a F2/N2 mixture with 12.5% F2 by volume at 0.1 MPa and 85 °C for 30 min. Physicochemical characteristics of the fluorinated surface layer were evaluated by ATR-FTIR and SEM techniques, and the results showed substantial chemical modification of the surface layer, which has a thickness of 0.89 μm and a roughened surface. Further, as expected on the basis of previous studies, measurements of surface electrical properties of the surface fluorinated sample, compared to the unfluorinated one, revealed a four orders of magnitude higher surface conductivity and a much more rapid decay of surface potential after corona charging. Dc flashover tests were performed on the truncated cone samples in SF6 gas at 0.1 MPa with a stepwise increasing voltage before and after the fluorination. The flashover test results showed a definite improvement in dc flashover voltage. For example, the flashover voltage at 63.2% probability or the mean flashover voltage for 2 min duration of the voltage step increased by 13.8% or 13.6% after the fluorination. The performance improvement is mainly attributed to easy leakage and dispersion of the charge deposited on the surface fluorinated sample from the gas phase, due to high conductivity of the fluorinated layer. The flashover test results also showed the influences of the duration of the voltage step on the flashover voltage and on the increase rate of flashover voltage. This means that even the time constant of the fast gas phase charging should be larger than 2 min, and that there should be different influences of the inhomogeneous surface conduction between the virgin sample and the fluorinated sample.

Preparation of epoxy-based insulator and optimization of its thermal property by Taguchi robust design method in double base propellant grain application

Taguchi method (orthogonal array, OA9) was used to design an epoxy insulator by evaluating its glass transition temperature (Tg) for using in a double base (DB) propellant grain. In this design method, three epoxy resins based on diglycidylether bisphenol A (DGEBA), three polyamine curing agents and a DGEBA-based reactive diluent agent were used. The curing process of epoxy resins with polyamines was studied by Fourier transform infrared spectroscopy. The results showed that the curing process was completed at room temperature. The effects of four parameters including resin type, curing agent type, curing agent concentration and diluent quantity were investigated to design a resin formulation with a highest Tg after curing. The obtained results were quantitatively evaluated by the analysis of variance (ANOVA). The results of ANOVA showed that the highest Tg of 86.0 ± 9.0 °C was obtained for the optimum formulation of MANA POX-95 as epoxy resin, H-30 as curing agent and 52 phr H-30. The Tg measured by the experiment was 78.0 ± 0.9 °C. In addition, the single lap shear strength (adhesion strength) of the optimized insulator was measured at 13.66 ± 1.02 MPa. Pull-off test performed on the surface of DB propellant resulted a 1.935 ± 0.003 MPa adhesion strength.

Preparation and Property Study of Graphene Oxide Reinforced Epoxy Resin Insulation Nanocomposites with High Heat Conductivity

In this paper, graphene oxide reinforced epoxy resin nanocomposites were successfully prepared. Compared with unmodified epoxy resin, the heat conductivity of the graphene oxide reinforced epoxy resin nanocomposites had been improved while keeping the insulation performance. The tensile strength was investigated at both room temperature (300 K) and liquid nitrogen temperature (77 K). And the fracture surfaces were examined by scanning electron microscopy (SEM). Results showed that the materials had excellent mechanical properties, which could be advantages for the applications as insulating layer in low temperature superconducting magnets.

Mechanical Fracture Characteristic of Epoxy Insulation Barrier for High Voltage GIS

Mechanical Fracture Characteristic of Epoxy Insulation Barrier for High Voltage GIS

Numerical simulation of quench protection for a 1.5 T persistent mode MgB2 conduction-cooled MRI magnet

The active quench protection of a 1.5 T MgB2 conduction-cooled MRI magnet operating in persistent current mode is considered. An active quench protection system relies on the detection of the resistive voltage developed in the magnet, which is used to trigger the external energizing of quench heaters located on the surfaces of all ten coil bundles. A numerical integration of the heat equation is used to determine the development of the temperature profile and the maximum temperature in the coil at the origin, or ‘hot spot’, of the quench. Both n-value of the superconductor and magnetoresistance of the wire are included in the simulations. An MgB2 wire manufactured by Hyper Tech Research, Inc. was used as the basis to model the wire for the simulations. With the proposed active quench protection system, the maximum temperature was limited to 200 K or less, which is considered low enough to prevent damage to the magnet. By substituting Glidcop for the Monel in the wire sheath or by increasing the thermal conductivity of the insulation, the margin for safe operation was further increased, the maximum temperature decreasing by more than 40 K. The strain on the MgB2 filaments is calculated using ANSYS, verifying that the stress and strain limits in the MgB2 superconductor and epoxy insulation are not exceeded.

Determination of Hydrophobic Contact Angle of Epoxy Resin Compound Silicon Rubber and Silica

Epoxy resin is a thermosetting polymeric material which is very good for application of high voltage outdoor insulator in electrical power system. This material has several advantages, i.e. high dielectric strength, light weight, high mechanical strength, easy to blend with additive, and easy maintenance if compared to that of porcelain and glass outdoor insulators which are commonly used. However, this material also has several disadvantages, i.e. hydrophilic property, very sensitive to aging and easily degraded when there is a flow of contaminants on its surface. The research towards improving the performance of epoxy resin insulation materials were carried out to obtain epoxy resin insulating material with high water repellent properties and high surface tracking to aging. In this work, insulating material was made at room temperature vulcanization, with material composition: Diglycidyl Ether Bisphenol A (DGEBA), Metaphenylene Diamine (MPDA) as hardener with stoichiometric value of unity, and nanosilica mixed with Silicon Rubber (SiR) with 10% (RTV21), 20% (RTV22), 30% (RTV23), 40% (RTV24) and 50% (RTV25) variation. The usage of nanosilica and Silicon Rubber (SIR) as filler was expected to provide hydrophobic properties and was able to increase the value of surface tracking of materials. The performance of the insulator observed were contact angle of hydrophobic surface materials. Tests carried out using Inclined Plane Tracking procedure according to IEC 60-587: 1984 with Ammonium Chloride (NH4Cl) as contaminants flowed using peristaltic pumps. The results show that hydrophobic contact angle can be determined from each sample, and RTV25 has maximum contact angle among others.

Resistance of surface fluorinated epoxy resin to corona discharge in SF<inf>6</inf> gas

Our previous results have shown that direct fluorination can modulate surface electrical properties and suppress surface charge accumulation of epoxy insulators, and thus has potential applications for improving the flashover performance of epoxy spacers in gas-insulated equipment. In this study, to investigate the resistance of the fluorinated epoxy surface layer to partial discharge in SF 6 gas, surface fluorinated epoxy samples together unfluorinated (virgin) ones were corona treated using a multi-needle-to-plate electrode system. ATR-IR analyses and SEM surface and cross section images show that the corona discharge caused the chemical modification and chain scission at some weak points in the fluorinated layer and the crosslinking reaction, and thus led to the formation of nodules on the corona treated fluorinated surface. However, the corona treatment did not change the fluorinated layer thickness. In contrast with this, severe degradation, most likely in the form of etching, occurred for the virgin surface layer during the same treatment. Measurements of surface potential decay and water contact angle indicate that the corona discharge obviously reduced surface conduction of the fluorinated sample, and rendered the surface conduction insensitive to humidity although the corona treatment almost did not change surface wettability of the fluorinated sample. On the contrary, the measurements show that surface conduction of the virgin sample increased and became sensitive to humidity after the corona treatment.

Detection of intense partial discharge of epoxy insulation in sf6 insulated equipment using carbonyl sulfide

Basin insulators in gas insulated switchgear (GIS) are prone to failure by partial discharge (PD). Insulation diagnosis using gas analysis method has advantages of strong anti-interference ability and high detection precision. This paper reports a new characteristic gas Carbonyl Sulfide (COS) for the detection of PD in epoxy insulators of GIS. The generation of COS is verified by experiments with trace gas detection technique. Experimental results indicate that COS is generated only when the intensity of PD is strong enough to cause flashover on the epoxy insulators. The corresponding production mechanisms of COS have been clarified using quantum chemistry calculations. To assess the PD level using COS, the relationship between discharge power and growth law of the concentration of COS is obtained from the experiments, which indicates that COS could be used as an effective characteristic gas to diagnose epoxy solid insulation of GIS concerning high energy discharge.

Light-Weight Silver Plating Foam and Carbon Nanotube Hybridized Epoxy Composite Foams with Exceptional Conductivity and Electromagnetic Shielding Property.

Herein, light-weight and exceptionally conductive epoxy composite foams were innovatively fabricated for electromagnetic interference (EMI) shielding applications using multiwalled carbon nanotubes (MWCNTs) and 3D silver-coated melamine foam (SF) as conductive frameworks. A novel and nontraditional polymer microsphere was used to reduce the material density. The preformed, highly porous, and electrically conductive SF provided channels for fast electron transport. The MWCNTs were used to offset the decrease in conductive pathways due to the crystal defects of the silver layer and the insulating epoxy resin. Consequently, an exceptional conductivity of 253.4 S m(-1), a remarkable EMI shielding effectiveness of above 68 dB at 0.05-18 GHz, and a thermal conductivity of 0.305 W mK(-1) were achieved in these novel foams employing only 2 wt % of MWCNTs and 3.7 wt % of silver due to the synergistic effects that originated in the MWCNT and SF. These parameters are substantially higher than that achieved for the foam containing 2 wt % MWCNTs. Also, the SF exhibited little weakening in the foamability of the epoxy blends and the compression properties of resulting foams. All the results indicated that this effort provided a novel, simple, low-cost, and easily industrialized concept for fabricating light-weight, high-strength epoxy composite foams for high-performance EMI shielding applications.

The Scrutiny of the Insulation Breakdown Strength for the Nanocomposite Oxide Doped Epoxy Resin Insulator with Different Electrodes by Using Positive Impulse Voltage

This research presents the ratio of doping nanocomposite oxides in dielectric materials for increasing the efficiency strength and endurance voltage. Tests were conducted and analyzed the characteristics of epoxy nanozinc oxides. By using positive standard impulse voltage abilities of nanocomposite oxides were used as electrical insulators-epoxy resin doped with zinc oxides nanocomposite in ratios of 0, 5, 10, 15, and 20% by weight. And the design of electrodes embeds in the specimens with 4 types of electrode, as needle electrode, point electrode, spherical electrode and the partial spherical electrode. When adjusted the impulse voltage level of 75kV to the specimen immersed in transformer oil. The experiment aforementioned to investigate the ratios damages on insulator surfaces and the number of breakdowns. The microscopes with magnification levels of 20-800X were used to view the damages on insulator surfaces. Results, it was found that regarding specimens used for doping an epoxy resin with zinc oxides nanocomposite in a ratio of 5% had high withstand insulator with electrode types. The partial spherical electrode tested with positive impulse standard voltage has destructive distance lower damage than other electrode types.

Improved resistance of epoxy resin to corona discharge by direct fluorination

Our recent studies have indicated that direct fluorination can modulate surface electrical properties and suppress surface charge accumulation of epoxy resin insulators. Further, to investigate the resistance to corona discharge of the fluorinated surface layer, the surface fluorinated epoxy sample together the unfluorinated (virgin) one were corona treated in synthetic air using a multi-needle-to-plate electrode system. ATR-IR and EDS analyses and SEM surface and cross section images show that the corona treatment did not lead to cleavage of the C-F bond in the fluorinated layer and to changes in its surface morphology and thickness, although the treatment attacked the cross-linked products generated by fluorination and the weak points at which the fluorine substitution or addition reaction took place only partially. In contrast with this, the virgin surface layer was degraded by the corona treatment, likely in the form of ablation. Measurements of surface potential decay and water contact angle indicate that the corona treatment caused a decrease in surface electrical conduction of the fluorinated sample due to the attack on the cross-linked products and the weak points, but did not change its surface wettability and did not produce soluble degradation products in the fluorinated layer. On the contrary, the measurements show that the corona treatment led to an increase in surface conduction of the virgin sample, and surface conduction of the corona treated virgin sample was highly sensitive to the humidity due to the presence of soluble degradation products on the surface.

에폭시 절연의 전기적 트리잉에 관한 표면 개질된 나노알루미나의 영향

This paper presents the results of a study on the effect of surface modified alumina nanocomposites on electrical tree growth in epoxy insulation. Treeing experiments were conducted at a fixde AC voltage (500kV/mm, 10kV/60Hz)on unfilled epoxy sample as well as epoxy nanocomposites of 4 types with different loading and surface modified GDE gram. Time for tree growth as well as tree propagation length were studied. The results show that there is a significant improvement tree propagation time compare unfilled epoxy to epoxy nano alumina composites. Different tree propagation shapes as well as slower tree growth with 4 types nano alumina composites were observed.