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The carbon oxides (CO2 and CO) in the insulating oil of power transformers come from the thermal aging of cellulosic insulating paper; the CO2/CO ratio can reflect the aging state of cellulosic insulating paper. At present, the formation mechanisms of CO2 and CO in oil-immersed power transformers are still unclear. In this article, the ReaxFF reaction force field is used to simulate the thermal aging process of cellulosic insulating paper, and the main reaction pathways of CO2 and CO molecules formed by cellulose pyrolysis are obtained. The study finds that the amount of CO2 and CO generated is related to temperature. When the pyrolysis temperature continues to rise, the amount of CO2 generated shows a downward trend, while the amount of CO generated continues to increase, and the CO2/CO ratio continues to decrease. The simulation results are consistent with the previous experimental results. Through pathway tracking, it is found that the CO2 and CO molecules are mainly derived from certain specific atoms of cellulose molecules. The COSMO-RS module is used to analyze the change trend of the solubility of CO2 and CO in insulating oil with temperature. The results show that the solubility of CO2 and CO decreases with the increase of insulating oil temperature, which provides theoretical support for accurate application of carbon oxides aging evaluation index at different temperatures. [ABSTRACT FROM AUTHOR]

Oil soluble chemical markers such as methanol, ethanol and 2-furaldehyde for assessing the condition of insulating paper still present many challenges for an accurate interpretation in real transformers. Indeed, many conceptual parameters such as design (shell vs. core) or type of cooling are needed for a more accurate interpretation of the data. Moreover, similarly to water, the measured marker concentrations in oil are temperature-dependent, i.e. an existing partition phenomenon between the oil and the solid insulation modify the solubility of the markers, thus changing their apparent concentrations in the oil. Consequently, to follow the real trend of these species during the transformer?s service life, it is crucial to correct their concentrations at a specific temperature, as is done for the water content. Knowing these facts and in order to calibrate a predictive model, Hydro-Qu?bec decided to access equipment when dismantled, which enables a large amount of paper to be sampled from different sections of the windings. This allows for a more accurate representation of the transformer paper conditions in relation to transformer design. The paper condition obtained by measuring the degree of polymerization in accordance with the presence of chemical markers is a valuable process. We believe that it is possible to better understand the behavior of the paper insulation and to assess markers concentration thresholds using the oil analysis. This article discusses the recent experience in this field with specific cases. [ABSTRACT FROM AUTHOR]

Different wood-fibre based papers were characterized by dielectric spectroscopy, mechanical testing and microscopy. The data obtained were utilized to investigate the relationship between the chemistry, morphology and density of a paper and its permittivity and dielectric loss. The density strongly influences the dielectric response, but the response is not affected by the way the density has been achieved; by pressing the paper during drying or by mechanical treatment of the fibres before sheet preparation. The chemical composition of the pulp influences the polarization, dielectric loss and charge transport. It was found that paper-vacuum and paper-oil combinations can be represented by series-equivalent circuits. The permittivity of paper made from electrical grade kraft pulp, used in e.g. high voltage transformers, without any porosity is estimated to be 5.3 and tan δ to 0.01- 0.02 at 50 Hz and 70 °C. The lignin and hemicellulose content of the kraft pulp do not affect the real part of the permittivity significantly, but the dielectric losses increase with increasing lignin and hemicellulose content in both oil and vacuum at 50 Hz and 70 °C. [ABSTRACT FROM PUBLISHER]

SF 6 /N 2 mixtures is considered as a practical alternative proposal of SF 6 in GIS and GIL. Simulating particle transportations and chemical reactions during the positive streamer propagation in SF 6 /N 2 mixtures assists in the insulation performance optimization of SF 6 /N 2 mixtures. This paper presents a fluid dynamic model coupled with the chemical reaction system for the positive streamer propagation in SF 6 /N 2 mixtures. The Townsend coefficients of the 20%SF 6 /80%N 2 mixture derived from the proposed chemical reaction system are in accordance with the measurement results. Based on this model, the propagation of the positive streamer in a 1 mm needle-plate gap in the 20%SF 6 /80%N 2 mixture is simulated. Simulated results indicate that there exists a negative space charge region in the streamer channel. It can be attributed to the increasing attachment rates of SF 6 yielding SF 5 − and SF 6 −, and the reduction of the ionization rates of N 2 and SF 6 in the streamer channel. Besides, it is noted that the ionization activities of N 2 and SF 6 at the streamer head are equally important to support the continuous propagation of the positive streamer. The ionization of N 2 in the streamer channel serves as an important factor to supply electrons and avoid the accumulation of the negative space charge. [ABSTRACT FROM AUTHOR]

The effects of liquids immersion and subsequent drying on the surface properties of filled high temperature vulcanized (HTV) silicone rubber have been reported in this series of paper. In this first paper, the surface hydrophobicity characterized by static contact angle and surface chemical properties characterized by a comprehensive analysis of Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and thermal desorption gas chromatography mass spectrometry (TD-GC/MS) have been studied. The liquids employed in this study were deionized water, NaCl solution and nitric acid solution, which represented the actual liquids that composite insulators could encounter in practice use. As for the NaCl solution, the lower the concentration, the greater its impact on the hydrophobicity of the silicone rubber (the deionized water can be considered as the NaCl solution of concentration of 0 mol/L). As for the nitric acid solution, the higher the concentration, the greater its impact on the hydrophobicity of silicone rubber. During the permeation process of deionized water and NaCl solution into HTV silicone rubber, some Alumina Tri-hydrate (ATH) filler and low molecular weight (LMW) could be dissolved into the liquids. Nitric acid solution not only dissolved the ATH filler, but also interacted with the ATH filler and degraded the polymer matrix. [ABSTRACT FROM AUTHOR]

SF6 is widely used in C-GIS as an insulating medium. However, SF6 and its decomposition products can pollute environment and harm human health and equipment. Firstly, this paper verifies the high-energy discharge promotes CF3I to produce C2F6 and I2 by simulation. Therefore the paper puts forward the significance of using mixture gas to reduce the use of CF3I and control the produce of I2. Secondly, the partial discharge inception voltages in the positive half cycle of power frequency (PDIV+) of CF3I/CO2 under different pressures, mixing ratios (k) and interelectrode distances were measured and compared with SF6/CO2. The results show that: when k is more than 10%, the PDIV+ of CF3I/CO2 is close to or higher than SF6/CO2 in the same experimental conditions; The PDIV+ of CF3I/CO2 (30%-40%) at 0.15-0.2MPa can reach the level of pure SF6 in 0.1MPa. The breakdown experiments under different electric fields shows that the breakdown characteristic of CF3I/CO2 (30%-40%) at 0.15-0.2MPa can exceed the level of pure SF6 at 0.1MPa. Considering the boiling point, producing of I2 and insulating property, CF3I/CO2 (30%-40%) is likely to replace SF6 used in C-GIS. [ABSTRACT FROM AUTHOR]

This paper is aimed at the characteristics of treeing phenomena developing in EPDM (Ethylene Propylene Diene Monomer) in a point ? plane electrode arrangement and the resulting damages when subjected to ageing AC voltage. It reports mainly on the measurements of the partial discharge inception voltage (PDIV) and partial discharges (PDs) accompanying the evolution of tree structures, the dissipation factor (tg?) and capacitor (Cx) of insulation as well as the chemical analyses that are Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to identify the changes in the morphology and microstructure of damaged polymer. The obtained results evidence the fact that the tree formation is linked to the appearance of partial discharges which are promoted by off-gases forwards to the material microstructure modification. [ABSTRACT FROM AUTHOR]

This paper presents a nonedible karanji base vegetable oil (VO) as an alternative transformer oil. The nature of biodegradability, environment friendly and easy availability makes this oil a suitable candidate for liquid insulation. The crude karanji oil (CKO) is not at all suitable for the transformer use because of the higher acid number and viscosity, it will affect negatively on the heat transfer and flowability of liquid inside the transformer. Two step transesterification process has been followed for the extraction of karanji oil methyl ester (KOME) from CKO. Characterizations like Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR) and gas chromatography-mass spectroscopy (GCMS) of the KOME are carried out to ascertain the formation of methyl ester oil. Thermophysical properties such as thermal conductivity, viscosity, density, interfacial tension, colour, flash point, pour point, chemical properties such as acid and iodine number, moisture and electrical properties such as dielectric strength, dielectric dissipation factor, and dielectric constant are measured as per standard and compared with mineral oil (MO). AC breakdown voltage (ACBDV) of the KOME is studied and the Weibull statistical analysis is carried out at 95% confidence interval to evaluate breakdown probability. Oxidative ageing of MO and KOME are performed and the effect of thermal conductivity and ACBDV with ageing are studied. It is observed from the results that the performance of the KOME is superior then MO for transformer application. [ABSTRACT FROM AUTHOR]

This work studies the space charge mechanisms of PE and PTFE by involving the combination of electronic structures and charge transfer processes at the interfaces of electrode/dielectrics. Experimentally, significant positive charge packets were observed in LDPE when subjected to a high electric stress. However, slight charge accumulations (mainly homo-charges) were observed inside polytetrafluoroethylene (PTFE) under the same condition. The electronic structures of PE and PTFE were calculated by density functional theory (DFT). After that, we obtained the electronic parameters, such as energy level, Fermi level, band gap and electron affinity. A negative electron affinity is determined in PE, indicating an interchain electron charge transport at the bottom of the conduction band. Nevertheless, a positive electron affinity in PTFE exhibits an intrachain electron charge transport. Moreover, injection and charge transfer at electrode/dielectrics interfaces were studied based on the calculated parameters. A low hole injection barrier dominates the positive charge injection and accumulation in LDPE, while a high electron barrier hinders the electron charge injection. In contrast, the hole injection barrier of PTFE is higher than that of LDPE. We discussed these different processes in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a new vegetable oil that is jatropha curcas seeds oil as a substitute for mineral oil. This product has several advantages among which the fact that it is non-food crops and may be grown on low fertile soils and areas where annual rainfall levels are significantly lower than those required by other plants used to extract other vegetable oils such as rape-seeds, sunflower, corn, soybeans, grape-seeds and sesame. The considered natural ester oil is processed by alkali base catalyzed esterification process using potassium hydroxide (KOH) to produce jatropha curcas methyl ester oil (JMEO). The physicochemical (water content, relative density, viscosity, acidity, visual examination, color, iodine number, corrosivity, flash point, pour point) and electrical (breakdown voltage under ac, dc and impulse voltages) properties of JMEO are presented and discussed. A gas chromatography (GC) analysis is also achieved to identify the methyl ester components in JMEO. The breakdown voltage of JMEO is compared to that of mineral oil (MO). It is found that the average breakdown voltage of JMEO and MO under different voltage waveforms are too close. [ABSTRACT FROM AUTHOR]

In cable manufacturing industries, electron beam radiation is widely used to improve the performance of the polymeric materials. To analyze the effect of electron beam irradiation on the novel blends of SIR-EPDM of different composition, they were exposed to three different doses of electron beam irradiation 50, 150 and 250 kGy. The electrical properties like Volume Resistivity (VRY) and Surface Resistivity (SRY) of the SIR-EPDM blends were found as per ASTM/IEC standards. Also the mechanical properties such as Tensile Strength (TS), Elongation at Break (EB) and Hardness (H) of the SIR-EPDM blends were determined as per ASTM/IEC standards. This paper evaluates the changes in performance of various compositions of electron beam irradiated SIR-EPDM blends. The electrical properties of EPDM rich blends were found to improve for most of the doses of electron beam irradiation. Also considerable improvements in tensile strength have been noticed in some blends for certain doses of electron beam irradiation. [ABSTRACT FROM AUTHOR]

Charge accumulation under high voltage DC is a major concern in the transmission system as its presence distorts the local electric field. By performing chemical treatment on polymeric insulation via fluorination process, the charge transport characteristics of the material can be modified. In doing so, excellent surface properties of fluoropolymers can be attained without compromising the bulk properties of the original polymeric insulation. The change in chemical components at the surface of polymeric insulation should lead to a corresponding change in electrical properties at the surface and so suppress charge accumulation. In this paper, epoxy resin samples were formulated and treated with various surface fluorinating conditions. The samples then were characterised by scanning electron microscope (SEM), Raman spectroscopy and DC surface conductivity measurements. The surface potential decay measurement was performed and the result shows that there is a significant change in surface potential decay measurement with the introduction of surface fluorinated layer. The pulsed electroacoustic (PEA) measurement was used to further explain the decay mechanisms responsible for the observed phenomena. Surface DC flashover test using a pair of finger electrodes had also been conducted. It has been found that the introduction of fluorinated surface layer on epoxy resins plays an important role in improving the surface dielectric properties as apparent from the experimental results. [ABSTRACT FROM AUTHOR]

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. In these lines, corona discharge even occurs on well-designed hardware and insulators, which can inject charge into the insulator surface. The existence of surface charge has a marked effect on insulation degradation and plays an important role during the development of the surface flashover. Direct-fluorination is a method to change the chemical component, which could induce the corresponding changes in electrical properties of the surface layer, thus influencing the charge injection. This paper tries to study the effect of fluorination time on surface charge accumulation and decay of room temperature vulcanized (RTV) SiR. The samples were fluorinated in a laboratory vessel at 298 K (25 °C) using a F2/N2 mixture with 12% F2 by volume at 0.05 MPa (500 mbar) for 5, 10, 15, and 20 minutes. The sample surface chemical composition was analyzed by means of ATR-IR. The behavior of surface potential under dc voltage was recorded at room temperature with a relative humidity of ~ 40%. Obtained results show a dependence of the surface potential and the dissipation time upon the fluorination time, varying with the charging time. It is suggested that the direct fluorination can significantly suppress the accumulation and accelerate the decay of the surface charge. [ABSTRACT FROM AUTHOR]

In recent years, the multilayered polyimide films have been widely used in flexible Print- Circuit Board in order to reduce the thickness of the combination of the flexible Print- Circuit Board. The existence of space charge as a main reason for dielectric breakdown, has a great effect on breakdown characteristic. So it is important to study the space charge characteristics of the multilayered polyimide films. Fluorination can change the chemical component in surface layer of polymers and therefore can influence the charge injection from electrodes and affect the electrical properties of the surface layer. This paper presents a study aimed at clarifying the effect of fluorination on space charge behavior in multilayered polyimide films. Samples were fluorinated in a laboratory vessel at 328 K (55 °C) using a F2/N2 mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. The surface chemical compositions of the films were characterized by attenuated total reflection infrared analysis. The space charge distributions in multilayered polyimide films were measured by using the pulsed electroacoustic (PEA) method. Obtained results showed that the space charge distribution of multilayered film stacking with five fluorinated samples was quite different from that of multilayered film stacking with five untreated samples. It is also suggested that the fluorination can significantly suppress the injection of space charge. [ABSTRACT FROM AUTHOR]

The paper examines the models proposed by Zeller for the development of water trees within the polyethylene (PE) insulation of underground distribution cables. Those models are of two different geometries idealizing a water tree: a prolate spheroid and ageometry where two spheres are linked by a narrow conducting channel. In these models a dissolved species, within a solution permeating the water tree, enhances the conductivity of the solution, distorting the electric field and increasing the Gibbs? free energy. Consequently, the solute species have a chemical potential that is greater than that in the absence of an electric field and this potential is suggested as leading to reaction of the solute with PE. Zeller used sodium chloride as the solute and did not take into account (nor suggest) any reaction product in solution. Consequently, the chemical potential difference between reactants and products, the true "driving force" for reaction, was not obtainable from this previous work. The present paper suggests alternative species (ferric and ferrous iron) that can serve as reactant and product in a plausible reaction with PE. Calculation of chemical potential differences, based on both aspheroidal model and a uniform property dumbbell model, suggests that these species might indeed be involved in PE degradation but only at low solute concentrations. The paper concludes by hypothesizing how such low concentrations may occasionally occur. [ABSTRACT FROM AUTHOR]

Insulating liquids (transformer oils) are dielectrics used in a wide range of electrical equipment and provide a medium for both insulation and cooling. During equipment operation, liquids are subjected to electrical and thermal stresses. With continued use, they chemically degrade and produce degradation products and aging markers. In this study, models based on Fourier-transform infrared spectroscopic (FTIR) measurements of liquids are proposed for estimating insulating liquid properties (acidity, interfacial tension (IFT), and density) using only a single measurement combined with spectral data analysis. Estimation models based on artificial neural networks (ANN) and partial least squares (PLS) were developed through training and validation on approximately 850 samples of mineral insulating liquids. The proposed models provide an effective means for estimating the acidity, IFT, and density of mineral insulating liquids. The models provide estimation results comparable in reproducibility to standardized laboratory analyses, provide the means for a rapid and accurate assessment of the condition of the insulating liquid, as well as allow the design of dedicated sensors to perform these analyses online. [ABSTRACT FROM AUTHOR]

Environmental stress such as unintended exposure of aircraft wire insulation to aviation-related fluids is one cause of wire aging that increases the risk of electrical failure. In this paper, the dielectric properties of nylon 6, a common wire insulation material, were investigated under chemical exposure for up to 8 days in six fluids: distilled water, cleaning fluid, isopropyl alcohol, deicing fluid, jet fuel and hydraulic fluid. Real permittivity ε') and dissipation factor (D) of aged samples were measured using an LCR meter over frequency range from 100 Hz to 1 MHz in an ambient environment (23 °C). It was found that ε? and D of aged nylon 6 exhibit distinct shifting behavior according to the polarity of the fluids in which it is immersed. Immersion in polar fluids gives rise to a strong effect of fluid absorption on the increase of polarizability of nylon 6, showing significant increase in ε? and D, along with moving of relaxations to higher frequencies. Electrical breakdown strength of nylon 6 was also observed to reduce dramatically following exposure to polar fluids. A two-parameter Weibull distribution was applied to analyze the distribution of electrical weak sites in chemically-aged nylon 6 and it is concluded that a different electrical breakdown mechanism could be responsible for the narrower distribution observed after polar chemical exposure than for the pristine material. Nylon 6 displayed resistance to aging in non-polar fluids, showing no significant change in complex permittivity and electrical breakdown strength. [ABSTRACT FROM AUTHOR]

In the present paper, Differential Scanning Calorimetry (DSC) has been applied to bring out the role of zinc naphthenate accelerator in the curing of epoxy-anhydride pressure impregnant used for impregnation of electrical machines. Effect of concentration of zinc naphthenate on curing behavior of bisphenol-A epoxy resin and methylhexahydrophthalic anhydride hardener has been studied by obtaining dynamic DSC thermograms for uncatalysed, and catalysed system with various concentration of zinc naphthenate. The investigations reveal that the un-catalyzed purified epoxyanhydride mix exhibits an endothermic peak at temperature around 260 °C in place of cure exothermic peak in the DSC curve. The analysis of DSC and TGA data of individual resin, hardener and their mix indicate that the endothermic peak is attributed to the evaporation of resin and hardener implying that the hardener does not react with resin in absence of accelerator. The addition of zinc naphthenate accelerator at concentration of 1 pph (parts of zinc naphthenate per hundred parts of resin- hardener mix) causes two exothermic peaks in the DSC thermogram. The position and area under these peaks vary with the accelerator content resulting in the variation in the processing parameters and the performance properties of the cured material. The first peak from esterification reaction appears between 90 and 200 °C and second peak from etherification reaction appears in the temperature range of 180 to 330 °C. The area under the first exothermic peak appearing at low temperature increases with increase of accelerator content and predominates at concentration of ⩾ 1.5 pph. The area under the second exothermic peak appearing at high temperature increases with the decrease of accelerator content and predominates at concentration of ⩽ 0.5 pph. The accelerator concentration of 2 pph provides maximum reactivity. [ABSTRACT FROM PUBLISHER]

Polyimide (PI) tape has been widely used as electrical insulation for wires and cables due to its excellent balance of electrical, mechanical and thermal properties. However, insulation materials are exposed to various environmental degradation mechanisms during service, which can cause deterioration of their insulation properties. In this paper, the effects of thermal exposure and immersion in water on dielectric strength of Kapton HN PI film are investigated statistically by two-parameter Weibull distribution analysis. The PI samples were heated at 475 °C for 1 to 4 h, and at 450 to 480 °C for 4 h, to study the influence of thermal exposure. Moreover, to explore the effect of moisture absorption, other PI samples were immersed in distilled water for up to 96 h at room temperature. After the degrading process, breakdown voltage and thickness were measured at 20 different points on each sample. The Weibull cumulative distribution function for each of the degraded samples was plotted, and compared with that of a sample dried by heating at 200 °C for 1 h. Significant decreases in both the scale parameter and the shape parameter of the Weibull distribution, obtained through least-squares regression, are observed, indicating a statistical decrease in dielectric strength and a more dense dispersion of electrical weak points in PI. This observed deterioration of insulation capability of PI is attributed to chemical degradation and formation of ionic side groups during heating and immersion in water, respectively. [ABSTRACT FROM PUBLISHER]

At the solid-liquid interface, a charge zone called the Electrical Double Layer (EDL) appears. It is constituted of two zones of opposite sign, one in the solid and another one in the liquid. When a liquid flows through a pipe, there is a disturbance of the EDL and an axial streaming current is generated. This current is due to the convection of the charges coming from the electrical double layer. In this paper, we present a numerical simulation of the EDL development process in the case of a liquid containing additives or impurities which are partially dissociated into positive and negative ones. We treat the case of laminar flow and an interfacial reaction whose conversion is small compared to the concentration of positive and negative ions in the bulk solution. The boundary conditions are deduced from the kinetics of the wall surface reactions with additives. However, in this paper, the formation of the EDL at the solid-liquid interface is investigated without any flow (static case). Thus, the rate of the wall reaction and the resulting charge concentration in the liquid can be studied. Then, once the equilibrium of physicochemical reaction is reached, convection is forced and the EDL dynamic behavior has been studied (dynamic case). The physicochemical reaction at the solid-liquid interface, the evolution of the space charge density in terms of both the axial coordinates and flow velocity, and the equations of conservation of charge of the liquid species have been implemented to a developed version of "Electricite de France" finite volume CFD tool Code_Saturne, which is designed to solve the Navier- Stokes equations. Finally, the simulation results of the dynamic behavior at different flow rates are compared with the experimental results. [ABSTRACT FROM AUTHOR]

Since gas evolvement deteriorates the dielectrical properties of insulating fluid, its ability to resist decomposition under electrical discharge is of paramount importance for the safety of power transformers under operating conditions. In this paper, a series of experiments have been performed under electrical discharge according to ASTM D6180. Various insulating fluids were considered. The samples include minerals oils, synthetic and natural esters, and silicone fluid. The results indicate that the gassing tendency of natural esters is much lower than their counterparts. No significant differences between synthetic esters and silicone fluid were observed. Severely hydrotreated and hydrocracked oils indicate a higher gassing tendency. It is also shown that service-aged oil gassing tendency decreases with reclamation passes. The reclamation of service aged oil by three commercially available Fuller?s Earth (FE) showed a declined gassing tendency when FE helped reducing the DDF and turbidity. In addition, the theoretical premises that, oil born decay products contribute to the oil gassing, is experimentally confirmed under laboratory conditions. Extended stability test (3 times longer than the standard specification) also provide convincing evidences that each brand of mineral insulating oil might contain a limited amount of unstable hydrocarbons and volatile compounds. This finding indicates that when in service conditions these are gradually decomposed, the gassing tendency should go down [ABSTRACT FROM AUTHOR]

This research intends to investigate the applicability of fullerene as an electrically insulating filler. So far, the authors reported that the addition of a very small amount of fullerene C 60 to epoxy resin (EP) improves the dielectric breakdown strength (Eb) by about 30%. This report presents the study on the effect of four different types of fullerenes as fillers added to EP on the improvement of Eb. Fullerenes used are mixtures of C 60 and higher order one C70 with a different mixture rate, and the addition effect of sublimation-purified fullerene on Eb is also investigated. Experimental results reveal that samples added with sublimated fullerenes exhibit larger Eb than that of samples without sublimation. The sublimation-purified sample is also found to give almost no difference in Eb by the type or proportion of the added fullerenes C60 and C70. An attempt is also made to discuss the mechanism of the improvement effect on Eb of fullerene by evaluating the electronic state of epoxies with different fullerene fillers and curing agent using quantum chemical calculation. As a result, it is shown that the introduction of C60 and C70 into the EP considering the curing agent introduces electron traps of 0.64 and 0.72 eV, respectively. It is interpreted that the introduced electron traps suppress the electron avalanche, and consequently improves the breakdown strength. [ABSTRACT FROM AUTHOR]

In this work, the space charge behavior and breakdown strength of polypropylene (PP)/ultralow density polyethylene (ULDPE) blends and three different radical scavenger modified composites are performed at 30, 60 and 90 °C. The trap distribution in the radical scavenger and the composites are investigated based on quantum chemistry calculation and isothermal discharge current test. The results show that, 0.3 wt% addition of radical scavenger has little effect on the thermal and mechanical property of the composites. The radical scavenger can introduce traps with different energy levels, which has greatly inhibited the space charge accumulation aggravated by the increasing temperature in the PP/ULDPE (PU) blends. Although the overall breakdown strength of the samples decreases with the rise of temperature, the performance of radical scavenger modified composites show the best, which suggests a great correlation with the traps they introduce, the molecular structure and chemical reaction of the additives themselves. The PP/ULDPE blends with 0.3 wt% C944 exhibit great potential for HVDC cable insulation. [ABSTRACT FROM AUTHOR]

This study investigates the characteristics of electrical trees in silicone rubber (SiR) samples after soaking in silicone grease (SG) for various times and exposed to switching impulses. The results show that the tree initiation probability increases from 60 to 100 % after SG soaking for 340 h when the impulse amplitude is 38 kV and the tree fractal dimension increases from 1.16 to 1.45. A similar trend is observed under negative impulse. It is suggested that SG soaking leads to a higher tree initiation probability and a larger tree fractal dimension. In addition, isothermal surface potential decay measurements are employed to obtain the trap parameters of SiR samples. Equilibrium swelling procedures are used to test the crosslinking density. The energy level and density of deep trap both decrease with SG soaking time, which is beneficial for the transport of charge carriers injected from the needle tip and further results in more severe scission of SiR molecular chains. Moreover, the expansion of free volume originating from the broken physical crosslinking structure allows more violent impact ionization of charges to occur, which can also aggravate the scission of SiR molecular chains. Therefore, the decreased tree resistance can be found in SiR after SG soaking. Furthermore, the polarity effects can be observed during the tree initiation and propagation process, which are mainly rooted in the different distribution of hole­type and electron-type traps. [ABSTRACT FROM AUTHOR]

Recent advances have allowed submicron features of electrical trees to be imaged. Until recently it has not been possible to analyze chemical aging on the same scale. Here, the use of atomic force microscopy — infrared spectroscopy (AFM-IR) to characterize chemical degradation around a needle tip, and in the vicinity of electrical tree branches grown in epoxy resin is explored. The spectral signatures associated with the degradation of epoxies during electrical treeing are successfully identified with 50 nm resolution. This allows identification of chemical degradation in unprecedented detail. The method of polishing and grinding to prepare the samples was found to remove degraded material from exposed channels. This issue was overcome by not fully exposing the tree, but bringing it close enough to the surface that the AFM-IR was able to see within the channel. A short tree examined immediately after initiation showed no chemical degradation, indicating that its growth was not a chemically active process, suggesting electromechanical fracturing is more likely. Mature channels showed no singular chemical signature. Carbonyl groups were identified in all mature channels and were particularly concentrated at the branching points studied, suggesting higher levels of degradation during branching or accumulation at points of bifurcation. It is believed that these reactions are precipitated by hot electron impacts during discharges. AFM-IR has provided unprecedented detail concerning chemical damage incurred during the treeing process and can provide vital information to inform models of aging. [ABSTRACT FROM AUTHOR]

By changing the ratio of resin to hardener, a series of epoxy resin samples has been produced with differing network structures and different retained chemical functionalities. The resulting materials were characterized by thermal analysis, dielectric spectroscopy, DC conductivity, and DC and AC breakdown strength measurements, to explore the effect of network structure and chemical composition on molecular dynamics and electrical properties. Differential scanning calorimetry showed that the glass transition temperature is primarily determined by the crosslinking density and indicates that, under the range of conditions employed here, side reactions, such as etherification or homopolarization, are negligible. Conversely, changes in DC conductivity with resin stoichiometry appear to occur as a result of changes in the chemical content of the system, rather than variations in network structure or dynamics. Specifically, we suggest that the DC conductivity is markedly affected by the residual amine group concentration in the system. While DC conductivity and DC breakdown appear broadly to be correlated, AC breakdown results indicated that this parameter does not vary with changing stoichiometry, which suggests that the AC and DC breakdown strengths are controlled by different mechanisms. [ABSTRACT FROM AUTHOR]

The present work studies the space charge accumulation and decay in the degassed cross-linked polyethylene (XLPE) by detrapping mechanism and quantum chemical method. Experimentally, significant positive charge packets were observed at room temperature (300 K). Negative charges accumulated strikingly under high temperatures but with a fast decay during depolarization. The estimated bipolar carrier mobility and electron/hole trap depth that derived from the charge decay characteristics indicated that a shallow trap distribution (0.84?0.9 eV) dominates the space charge behavior. Additionally, a high temperature (>60 ?C) benefits to evaluate the deep traps (0.9?1 eV). Quantum chemical analysis using density functional theory (DFT) demonstrated that both the localized states for shallow electron and hole traps exist in the electronic structure of the XLPE structures. The former is derived from the physical disorder and crosslinks. The latter is ascribed to the hopping interaction between the chain terminal and the other orientated chains. The calculation results about the charge trapping characteristics agree with the experiments. Furthermore, the role of charge injection at the electrode/dielectric interface is also discussed. [ABSTRACT FROM PUBLISHER]

Hole mobility in crystalline polyethylene (PE) is evaluated from an atomistic point of view, with the combination of quantum chemical calculation and kinetic Monte Carlo simulations. Hole hopping rate between PE chains are computed by Fermi?s golden rule and Marcus rate expression. It turns out that hole transfer in PE occurs in a hopping regime rather than in a band regime even for crystalline structure without any inherent structural disorders. The results indicate that in crystalline PE, hole hops between localized states that are created by polaronic effect. The hole mobility is strongly dependent on the chain length, and increases with increasing chain-length. When the chain length was comparable to the thickness of lamellar crystals, i.e., the characteristic length scale of crystal in the direction of c axis, hole mobility and activation energy for hole transfer were in reasonable agreement with experimental values. Simulated results support the experimental prediction that fast and slow mobility are due to charge transfer in the crystalline region and amorphous region, respectively. Our findings show that high hole mobility observed in crystalline PE, regardless of the small inter-molecular electronic couplings, is due to the small reorganization energy, which is realized through the intra-molecular hole delocalization, and due to quantum tunneling effects owing to the small energetic disorder and high-frequency intra-molecular phonon modes. [ABSTRACT FROM PUBLISHER]

The oxidation process induced in ethylene-propylene-diene (EPDM) copolymer by gamma irradiation was simulated by solving equations on chemical reactions and gas diffusion rates. As a result, distributions of oxidative products and gases and changes in material properties were clarified. All the oxidative products such as ketones, alcohols, and carboxylic acids, crosslinks between molecular chains, and chain scissions in EPDM increase with irradiation and they show concave spatial distributions inside the sample sheets. The simulation results demonstrates that EPDM becomes hard when it was irradiated by gamma rays and the increase in hardness is more significant at the surface of the sample sheet than its inside. Moreover, it was found that a low diffusion coefficient of oxygen in EPDM leads to the appearance of a clearer diffusion-limited regime of degradation. These simulation results are in good agreement with experimental results. [ABSTRACT FROM PUBLISHER]

Single component room temperature vulcanized (RTV-1) caulks are used in a variety of electrical and other applications. In high voltage Non Ceramic Insulators (NCIs) they are used as part of a triple seal system near the metal end-fittings to protect insulators against environmental stressors including moisture and acid ingress and salt contamination. In service they must resist chemical aging for long periods of time. MacLean Power Systems, Inc. provided three RTV-1 caulk materials for evaluation, of which all three materials maintained their hydrophobicity or increased their hydrophobicity during acid immersion and UV/condensation tests. However, all three materials showed significant mass and hydrophobicity loss upon exposure to salt water at elevated temperatures. Our results show that RTV-1 materials perform differently when compared to Silicon Rubber (SIR) insulator shed materials as reported in the literature when exposed to acid immersion. This is due to the absence of aluminum hydroxide in RTV-1, also referred to as aluminum trihydrate (ATH). Additional acid immersion testing was conducted with ATH resulting in depolymerization of the RTV-1 material. [ABSTRACT FROM AUTHOR]

It has been proven that hydroxyl (OH) radicals can be generated by streamer discharges across water surfaces under ambient atmospheric conditions. Hydroxyl radicals have the highest oxidation capability amongst all oxygen-based reactive species, thus OH play an important role in oxidation of organic molecules and the bactericidal effects of plasma discharges. In this study, generation of hydroxyl radicals in water by pulsed streamer discharges was investigated. Terephthalic acid was used as a chemical probe as this acid is converted into 2-hydroxyterephthalic acid (HTA) by chemical reaction with OH radicals. The concentration of OH radicals was quantified by measuring the fluorescence light intensity generated by HTA molecules in water solutions. Both positive and negative pulsed discharges with different voltage levels were tested. Two different types of sample holder ? non-conductive plastic dishes, and dishes lined with conductive aluminum foil ? were used in order to investigate the effect of the discharge propagation path on the efficiency of OH production. The efficiency of OH production was measured as a function of: the distance between the needle electrode and the water surface; the magnitude and polarity of HV energization; and the total delivered charge. The obtained results will help in optimization of non-thermal plasma systems for chemical and biological decontamination. [ABSTRACT FROM PUBLISHER]

We studied the trapping of positive and negative charges in the chemical structures of polymers under a high electric field using a space charge measurement system. Positive charges accumulated in low-density polyethylene (LDPE), whereas positive and negative charges accumulated in polyimide (Kapton) and also in ethylene tetrafluoroethylene (ETFE) subjected to electron beam irradiation. To determine the charge-trapping sites in the chemical structures, a quantum chemical calculation was carried out using Density Function Theory (DFT) with Gaussian 09. The relationship between the energy band and the isosurface of orbital electrons at various energy levels was obtained. A threedimensional (3D) electrostatic potential distribution map was obtained for positively and negatively charged polymers to determine the relationship between a trapping site and the charge accumulation center in the 3D potential distribution map. Positive and negative charges in Kapton and ETFE films are trapped in trapping sites in chemical structures and the positive charges in an LDPE film are trapped in physical defects. [ABSTRACT FROM AUTHOR]

The effects of vapor with different chemical properties on corona partial discharges (PDs) at the junction section of the semi-conductive tape and the stress grading tape of stator windings were investigated. The phase resolved partial discharge (PRPD) patterns were collected during the experiment to obtain the characteristics of the PDs. The result has confirmed that relative humidity (RH) of the vapor with different chemical properties can cause corona discharge to change significantly. The acidic vapor can suppress corona discharge effectively. When RH exceeds 60%, the corona discharge would be hardly induced even though the voltage is boosted up to twice the operating voltage. When RH is over 80%, corona discharge will develop into phenomenon of creeping on the surface of the ground wall insulation and can hardly be collected through the capacitive coupler. [ABSTRACT FROM AUTHOR]

A new degradation model for safety cables in nuclear power plants that incorporates the critical antioxidant concentration concept is proposed in order to account for the effect of antioxidants and to simulate several synergisms in various thermal and radiation environments. A chemical reaction scheme is used to represent oxidation reactions via the decomposition of peroxide radicals. The effects of antioxidants are included in this scheme in order to demonstrate critical concentration phenomena. In addition, diffusion equations are added to the reaction rate equations to enable reproduction of diffusion-limited oxidation. Such a degradation model with antioxidant effects is discussed for degradation behaviors in polymers used for safety cables under various dose rates and temperature conditions, and its effectiveness is verified. [ABSTRACT FROM AUTHOR]

The Kapton 100HN polyimide films were aged under 3 kV ac voltage (50 Hz), and the aging evolution were studied by the Fourier transform infrared spectroscopy (FTIR) and the dielectric measurement. The FTIR spectra show that the ether linkage, and some of C-H bonds in aromatic rings and C-N-C bonds transverse stretching vibration in imide are firstly broken by corona discharge. Then, with the increase of aging time, the cleavage of the imide group including C-N-C and C=O vibrations occurs. At the same time, the oxidative degradation produces compounds such as carboxylic acid, ketones, and aldehydes. Accordingly, the variations of dielectric constant ?1 and the dissipation factor tan ∂ are dependent on the formation of the polar groups and the breakage of some polar bonds in polyimide. [ABSTRACT FROM AUTHOR]

Cross-linking byproducts are suspected to be the main contributing factor in space charge formation observed in XLPE. To investigate the mechanism behind this phenomenon, low density polyethylene was soaked into three main crosslinking byproducts, acetophenone, α- methylstyrene and cumyl alcohol, and space charge measurements were performed using the Pulse Electroacoustic technique (PEA). It has been found that soaking LDPE in cumyl alcohol introduces more charges into the system, with homocharges and heterocharges accumulating within the sample compared to the additive free sample. In contrast, α- methylstyrene and acetophenone reduce the amount of accumulated charges. In terms of charge decay, all three byproducts enhance the decay process in the insulator. Further investigations were conducted in conditions where two byproducts are present in a sample. The results shows that acetophenone is a dominant byproduct in determining the charge density patter built up during the charging process, whilst the rate of charge decay is observed to be high in the presence of α-methylstyrene in the sample [ABSTRACT FROM PUBLISHER]

The interaction between iodine and polyethylene has been studied through the use of density functional theory (DFT) with the purpose of explaining the physical basis behind the increase in the conductivity of polyethylene upon doping with iodine. The interaction between polyethylene and various In stable configurations is characterized in terms of binding energy, bond lengths, electron charge density, changes in electron charge density, and mixing of atomic orbitals, all of which are determined through DFT. Based on the energy of iodine impurity states introduced into the bandgap and the spatial features of the impurity state wavefunctions, a mechanism by which iodine increases the conductivity of polyethylene is proposed. The mechanism explains the experimentally observed increase in hole mobility and decrease of activation energy of polyethylene upon doping with iodine. [ABSTRACT FROM AUTHOR]