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Here, piezoelectric transducers consisting of a P(VDF-TrFE) layer with either silver or PEDOT:PSS screen-printed electrodes are studied. The influence of electrodes on the dielectric and electroacoustic properties are studied in dielectric-spectroscopy and ferroelectric-hysteresis measurements. Only when both the bottom and the top electrodes are made of silver, the typical dielectric relaxation of the P(VDF-TrFE) layer is clearly observed. When one or two of the electrodes are of PEDOT:PSS, a Debye-like relaxation is present. Compared with silver electrodes, PEDOT:PSS electrodes allow for moderate self-healing. Consequently, samples with bottom and top PEDOT:PSS electrodes can be poled to saturation, while samples with silver electrodes can hardly be poled to saturation due to destructive electric breakdown. Acoustic transducer measurements show that silver electrodes facilitate higher and broader frequency operation, while PEDOT:PSS electrodes bring slightly lower total harmonic distortion. Overall, the acoustic performance shows no significant deviations between differently electroded samples so that silver electrodes do not offer any advantages for the transducers studied here due to their much higher tendency for destructive electric breakdown. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) film is the most commonly used dielectric film in power capacitor applications, thanks to its high breakdown strength combined with low dielectric losses. Today, antioxidants based on hindered phenol (HP) are mixed into the PP resin during manufacturing to provide thermal-oxidative protection during melt processing, however they increase the dielectric losses. Recently, a new PP-HP copolymer has been synthesized containing a few comonomer units with HP moieties, which are homogeneously distributed along the PP polymer chain. Addition of new PP-HP copolymer to PP dramatically improve the thermal-oxidative stability under elevated temperatures compared to neat PP. In the current study the electrical properties of this novel PP-HP copolymer and PP/PP-HP blends are investigated using dielectric spectroscopy and direct current (DC) breakdown strength. By adding lower amounts (2–5 wt%) of the PP-HP copolymer in PP, the dielectric constant and loss remains similar to that of neat PP. The short-term DC breakdown strength of the PP/PP-HP blends is equal or higher than the neat PP reference, combined with a reduced scatter in breakdown data. As a next step, long-term ageing tests of the PP/PP-HP blends are required. These findings may bring an advanced PP dielectric material into the market which is highly beneficial for high voltage power capacitor applications. [ABSTRACT FROM AUTHOR]

In nanocomposites, different surface states of nanoparticles can potentially provide different interactions with the base polymer and in turn change the bulk properties. Aluminium nitride (AlN) nanoparticles were surface functionalised with three different silane coupling agents (SCAs) with varying organofunctional and hydrolysable groups. The effects of the filler surface chemistry on the resulting AlN/polypropylene (PP) nanocomposites were examined and compared with an unfilled reference system. It is observed that different organofunctional groups can provide different nucleating effects and the dispersion states of nanoparticles while the hydrolysable group is not the dominant factor. The dielectric spectroscopy results show the hydrolysable group of SCA will also result in a difference of the interphase since the trimethoxy silane treated systems show much higher imaginary permittivity than the triethoxy silane treated systems when the frequency is below 1 Hz. The grafted organofunctional layer on the particle surface can provide a significant improvement of the thermal conductivity of the composite materials, e.g. 15 % improvement in thermal conductivity was observed when adding 10 wt% methacrylate silanes treated nano-AlN into PP, while the untreated counterpart only has 5 % improvement. [ABSTRACT FROM AUTHOR]

The aim of this paper was to investigate the correlation between the dielectric properties of biological tissues and their different states of hydration. Measurements were conducted on rat muscle and fat tissues both in vivo and ex vivo, in different states of dehydration through a loss on drying technique. Dielectric parameters were observed as a function of frequency from 500 MHz to 50 GHz by utilizing an open-ended coaxial probe at constant room temperature of 25° C. By observing which dehydration fractions fall within in vivo values, it was deduced that ex vivo samples are reliable in representing the dielectric parameters of in vivo samples, under certain controlled hydration conditions whereas, further analysis should be conducted for tissue characterized by low water content. [ABSTRACT FROM AUTHOR]

A custom-made modular high-precision dielectric spectrometer for quantifying aging-induced molecular changes in (sub-)picofarad polymeric samples is presented. Validation and characterization of the setup's performance is obtained by quantifying the change in the dielectric response of an epoxy polymer following the exposure to thermal, hygrothermal and ultraviolet radiation stress. It is shown that the observed changes in the dielectric spectra can be resolved with a relative precision better than 5·10−5 and are in line with previous studies employing commercial instruments on samples of higher capacitance. This setup is intended to serve as a blueprint for a sensitive and extensible (because modular) measurement tool for studying the pre-breakdown dynamics in low-capacitance recessed or disc-shaped specimens as used, e.g., in high-voltage insulation testing. [ABSTRACT FROM AUTHOR]

One of the challenges on the increasing reliance on isolated renewable generation sources is the transmission of power from these sources to centers of power demand. One possible approach is the use of high voltage direct current (HVDC) transmission. The power electronic converters are key components in HVDC transmission system. The converters produce the intended DC voltage for transmission but there may also be AC harmonics superimposed. The superimposed harmonics on the HVDC may have synergistic effects and may lead to further degradation in the cable insulation. Previous research has shown that partial discharge was the main cause of degradation in polymeric insulation under AC stress. However, few publications have demonstrated the effect of combined stress on cable insulation degradation. Additionally, the most popular cable insulation material, cross-linked polyethylene (XLPE), cannot be recycled. Alternative materials which can be recycled have been proposed and one such solution could be thermoplastic materials. In this study, HDPE was investigated as a reference material for thermoplastics and their potential use as insulation in HVDC cables. In this paper the effect of frequency on HDPE degradation under superimposed stresses was studied using the following approaches; equivalent phase resolved partial discharge (PRPD) plots, fourier transform infrared spectroscopy ? attenuated total reflection (FTIR-ATR) and dielectric spectroscopy (DS) measurements were carried out. The results show that during aging and with a frequency increase, the voltage of PD events increased which in turn created more polar molecule groups on the surface. The amount of polar molecule groups was found to affect ?' and tan?, with both increasing when more polar molecules were created. The results show that applying a higher AC frequency enhances polymer degradation. [ABSTRACT FROM PUBLISHER]

A large-area electro-thermal ageing test setup was developed and utilized to age several laboratory-scale biaxially oriented polypropylene (BOPP)-hydrophobic silica nanocomposite films. The films were aged in test capacitors with self-healing metallized film electrodes, which enabled the ageing test to continue beyond the first breakdowns. Eight different films were aged for 1000 hours under 100 V/?m DC stress at 75 ?C, and large-area DC breakdown measurements, dielectric spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and dielectric spectroscopy were used to detect localized and bulk degradation after the ageing period. The effects of antioxidant contents, different PP grades and compounder screw speed were evaluated. Material characterization indicates no bulk degradation had occurred during ageing, which was associated with moderate temperature stress and inert nitrogen atmosphere. On the other hand, low-field breakdowns (weak points) were observed in all but two of the aged materials, indicating that ageing was dominated by localized degradation which may have introduced new breakdown mechanisms. Weak points were also measured in a similarly aged commercial capacitor-grade BOPP film aged at a lower field, supporting this conclusion. The importance of long-term characterization in material development is demonstrated, and it is shown that long-term properties of the evaluated nanocomposites were at least on the same level compared to neat BOPP films. [ABSTRACT FROM PUBLISHER]

In this paper, the influence of partial discharges (PD) on the subsequent dielectric properties of oil-impregnated paper (OIP) is investigated. Dielectric frequency response (DFR) of OIP is investigated at varied levels of moisture, thermal aging, temperature, oil conductivity and electrode material, to allow comparison of these influences. It is shown that PD activity inside OIP can significantly change the real and imaginary parts of permittivity of the paper layers, especially in the frequency range below 100 Hz. It is shown that even if the PD activity is concentrated on a few percent of the test sample, the real part of permittivity measured on the entire sample after a few tens of hours of PD activity can increase up to 10 times at very low frequencies (∼ 1 mHz) and the imaginary part of the permittivity can increase up to 100 times at low frequencies (∼ 1 Hz). The change of the real and imaginary parts of permittivity due to PD activity is permanent. It is very similar to the change caused by thermal aging, and somewhat similar to the change caused by moisture and higher oil conductivity. It is also shown that the dissipation factor of OIP in contact with copper and brass increases, even in the absence of PD, but contact with aluminum and stainless steel has no influence on DFR of OIP. The results suggest that the influence of PD can be significant when estimating the moisture content or the level of thermal aging of OIP with DFR method. [ABSTRACT FROM PUBLISHER]

Epoxy resins modified with Glycidyl-POSS (Polyhedral Oligomeric Silsesquioxanes) in contents of up to 20 wt% were fabricated and studied in terms of dielectric spectroscopy, differential scanning calorimetry, AC breakdown tests, thermal conductivity measurements and corona resistance. Microstructure analysis have revealed a molecular dispersion of Glycidyl-POSS up to contents of 10 wt%, whereas in the 20 wt% POSS composites crystalline zones due to POSS could be observed by both scanning electron microscopy and transmission electron microscopy. All POSS composites have seen a significant improvement in AC breakdown strength, as well as an enhanced resistance to corona discharges, which in the latter case was getting more pronounced with higher POSS loadings. On the contrary, low POSS contents proofed most effective in improving the thermal conductivity, which should be attributed to the effect of POSS on the nanostructure of the polymeric network. [ABSTRACT FROM PUBLISHER]

Complex materials exhibit a dielectric behavior that can shed light on their chemophysical structure through a comprehension of the physical mechanisms originating that behavior. For the interpretation of a complex dielectric shape, where multiple relaxations are present (and usually described by semi-empirical functions), a correct interpretation of each simple relaxation is necessary. The separation of often closely overlapped relaxation curves requires the verification of the meaningfulness of such multiple relaxations and to determine their number and relative magnitudes, in other words to resort to a fitting procedure. However, often the physical interpretation of the fitting parameters is not straightforward, and their physical meaning is arguable. The application of even-order derivative spectroscopy is here demonstrated to be able to detect the presence and location of multiple dielectric relaxations, acting on the experimental data without any "a priori" hypothesis. [ABSTRACT FROM AUTHOR]

The presence of mobile charge carriers can affect the frequency response of complex permittivity of insulating liquid when the frequency is low. It has been found that the experimental results of the complex permittivity of mineral oils are in a good agreement with Coelho?s frequency response theory when an extra contribution to the complex permittivity arising from DC conduction is taken into account. It has been reported that small quantity of high mobility charge carriers are responsible for this DC conduction. In our previous work, we have found that if the charge carriers are fast enough so that they can reach the opposite electrode in a cycle, the motion of these fast charge carriers can only contribute to the imaginary part of the complex permittivity under a homogeneous field. In this paper, the polarization induced by the motion of those fast charge carriers under a non- homogeneous field has been studied. It has been found when the field is not high, the total current caused by the drift and diffusion of those fast charge carriers is proportional to the external voltage. A modified space charge polarization theory has been proposed. The frequency dependence of the complex permittivity obtained experimentally has been fitted using this modified Coelho model and compared with our previous simulation. This modified model enables one to gain a better understanding of the frequency response in mineral oil in low frequency regions. [ABSTRACT FROM AUTHOR]

In this study, the dielectric and thermal properties of nanostructured epoxy/POSS (Polyhedral Oligomeric Silsesquioxanes) composites were investigated, using a reactive Triglycidylisobutyl-POSS (TGIB-POSS) additive from 1 up to 10 wt%. POSS has been successfully dispersed at a molecular level for low content composites, which show a remarkably improved resistance to corona discharges, with up to 60% less eroded sample volume, along with significantly increased dielectric breakdown strengths and thermal conductivities. Epoxy/POSS composites containing 5 wt% and more of the POSS additive exhibit agglomerations, which have been observed by SEM. Furthermore, dielectric spectroscopy revealed additional interfacial loss peaks for such composites containing 5 wt% POSS and more, in addition to the α- and β-peaks known for epoxy. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) is a very promising material for application in high voltage insulation engineering due to its high thermal conductivity and good electrical insulating properties. In order to study the effect of incorporating BN particles in epoxy resin, composites with different filler sizes and several BN loadings have been fabricated. Two different filler sizes, one micrometric with an average grain size of 9 ?m and a submicrometric one with 0.5 μm, have been used to form composites. The amount of either type of BN in the matrix has been varied from 1 to 5 wt%. Dielectric and thermal performances of the test specimens have been assessed by means of Dielectric Spectroscopy, Differential Scanning Calorimetry, surface erosion, AC breakdown tests and thermal conductivity measurements. It has been found that incorporation of BN particles in the epoxy resin resulted in significant improvements of parameters such as resistance to electrical discharge, as well as diminished dielectric losses for the composites at higher temperatures. Furthermore, BN composites with 5 wt% filler loadings have shown a noteworthy enhancement of thermal conductivities, which was more distinct for the submicrometric BN composite. [ABSTRACT FROM AUTHOR]

In this paper, the rapid aging due to Partial Discharge (PD) activity was investigated in unaged and thermally aged oil-impregnated paper with a disk-shaped cavity between the sheets of paper. The PD inception voltage and the voltage for instantaneous breakdown were measured, and the time to breakdown was measured by applying voltages less than the instantaneous breakdown voltage. A comparison between time to breakdown of unaged and thermally aged paper shows no significant difference between thermally aged and unaged paper at sustaining PD activity. The time to breakdown as a function of applied electric field was plotted and compared for both cases showing points scattered around a line in log-log scale. Changes of the PD parameters, such as PD magnitude and PD repetition rate were analyzed from the beginning of PD activity up to the moment of breakdown. The results show that the number and magnitude of PD increase at the beginning of aging until they reach to a maximum value, then both quantities decrease slowly over time until the final puncture breakdown occurs. The results emphasize the importance of PD monitoring on real equipment with oil-impregnated paper as insulation system, such as power transformers, since a focus on the number and magnitude of PD at just the present time may mislead the interpretation. Dielectric spectroscopy measurements performed on unaged and thermally aged paper showed an increasing trend of ε" after the sheets of paper were exposed to thermal aging for longer time. Dielectric spectroscopy measurements performed on samples before and after exposure to PD activity showed a big change of ε", This change can be attributed to byproducts and ions produced by PD activity. [ABSTRACT FROM AUTHOR]

Because of the length scale and high specific surface area of nanometer-sized particles, they exhibit novel properties as compared with their bulk counterpart materials. Furthermore, the incorporation of well-characterized nanoparticles in various organic matrices provides dielectrics with improved electrical, mechanical and thermal features. Alumina and tantalum-pentoxide nanoparticles have been proved efficient fillers in such nanocomposites. These specific particles are herein produced by DC anodic arc-discharge immersed in water and they are probed by means of broadband dielectric spectroscopy in a wide temperature range (-100 to 100 °C). Different formalisms (effective dielectric constant, loss factor and specific conductivity) are combined, providing the possibility to determine the frequency and temperature dependence of the dielectric characteristics of the synthesized nanoparticles. The knowledge of the latter should be determinant for potential application of alumina and tantalum-pentoxide fillers to two-phase heterogeneous nanodielectrics. [ABSTRACT FROM AUTHOR]

Effects of interfaces and interphases in polydimethylsiloxane (PDMS) matrices with in situ synthesized titania (20 - 40 nm, in diameter) and silica nanoparticles (~5 nm), were studied employing dielectric and thermal techniques. The presence of the well dispersed inorganic particles and the hydrogen polymer - filler bonding result in a double effect on polymer mobility: suppression of crystallization and immobilization in a layer of a few nm around the particles. The effects were stronger in the case of titania nanoparticles, in consistency with stronger hydrogen bonding interactions, comparing to silica. Various contributions to the glass transition were recorded by both thermal and dielectric techniques, corresponding to bulk and modified polymer dynamics. The modified mobility originates from the restriction of polymer chains within the PDMS crystals and in an interafacial rigid amorphous PDMS layer around the nanoparticles. The thickness of the interfacial layer was estimated to 3-5 nm for titania and ~2 nm for silica. The mobile amorphous phase fraction giving rise to the glass transition was found to be nearly constant in the nanocomposites. The results were confirmed by employing various thermal (crystallization) treatments of the samples. [ABSTRACT FROM PUBLISHER]

This paper uses Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) techniques to study the molecular relaxations and phase transitions in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), which has been extensively studied as the active thin film in organic devices. Besides the identification of the glass transition, Β relaxation and crystal-to-crystal phase transition, we correlate such phenomena with dielectric and transport mechanisms in diodes with F8BT as the active layer. The Β relaxation has been assigned to a transition at about 210 K measured by 1H and 13C solid state NMR, and can be attributed to local motions in the side chains. The glass transition has been detected by DSC and 1H NMR. Dielectric spectroscopy (DS) carried out at low frequencies on diodes made from F8BT show two peaks which are coincident with the above transitions. This allowed us to correlate the electrical changes in the film with the onset of specific molecular motions. In addition, DS indicates a third peak related with a crystal-to-crystal phase transition. Finally, these transitions were correlated with changes in the carrier mobility recorded in thin films and published recently. [ABSTRACT FROM PUBLISHER]

Results of Frequency Domain Spectroscopy measurements are known to be largely influenced by environmental conditions, such as the temperature. Because field measurements, last hours after de-energizing the transformer, the ambient temperature may affect the results. Especially in cold regions of the world, extreme care are required to interpret the results when performing tests at relatively low surrounding temperatures. A better understanding and analysis of the dielectric test results are therefore only possible with a clear understanding of the physical behavior of the insulation system in response to the ambient conditions. In this contribution, the dielectric behavior of a composite oil paper insulation system has been explained from the properties of Debye basic model. A series of experiments have been performed under controlled laboratory conditions with preset moisture content inside the insulation. The equivalent circuit parameters of a laboratory made oil paper condenser bushing model were obtained using a non-linear optimization procedure. Since the dielectric parameters values are geometry dependent, poles, calculated from resistances and capacitances, were used as they are independent of the geometry. It was shown that the poles can be regarded as parameters able to be used for insulation condition assessment. [ABSTRACT FROM AUTHOR]

In this work, the complex permittivity of epoxy resin is measured. Earlier, we have shown that the inclusion of nanometric alumina particles (Al2O1), both as-received and pre-processed, improves the ability of a polymeric dielectric (epoxy) to resist degradation when exposed to surface discharges. In this work, we use dielectric spectroscopy to characterize neat epoxy (unfilled) and epoxy nanocomposites prepared with as-received and pre-processed Al2O3 nanoparticles. The dielectric spectroscopy measurements and analyses are carried out in the frequency range of 10-3 Hz to 10³ Hz and temperature range of 25 °C to 90 °C. Analyses of the data for neat epoxy indicate the presence of low frequency dispersion below 100 Hz. It is observed that the inclusion of nanoparticles lowers the effective real and imaginary permittivity of the composite material, at low temperatures. At higher temperatures, low permittivities are exhibited only by composites prepared with particles functionalized with silane before use. It is therefore seen that not only the presence of filler particles, but also the nature of the interface affects the dielectric properties. [ABSTRACT FROM AUTHOR]

in this paper, the water concentration profile within the insulation of a stator bar in the presence of a water leak is calculated by resolving the Fick's equation. The temperature strongly activates diffusion processes, but the shapes of concentration profiles remain similar. From the measured dielectric properties versus water content, an electrical model is developed in order to calculate the field and potential distribution within the insulation. The field is reduced in wet zones due to the high local permittivity and conductivity compared to dry zones. This effect is favorable since the breakdown field is lowered in wet zones. On the other hand, the field in dry zones is reinforced, but the value attained remains lower than the short-term breakdown strength. This explains why stator bars in the presence of waters leaks may survive for long times, in spite of high local water concentrations in excess of 1%. The high sensitivity of dielectric properties at low frequency to the presence of water suggests non-destructive methods to detect wet bars in a real power generator. [ABSTRACT FROM AUTHOR]

Water absorption in an epoxy composite used for insulation of stator bars in large generators is investigated in order to study both diffusion kinetics and effects on dielectric properties. Water absorption can be described by the superposition of two Fickian mechanisms, the first occurring within epoxy and the other at interfaces between epoxy and tillers. A large decrease of breakdown strength versus water uptake is observed. It points to the large deleterious effect of water on insulation reliability. Dielectric spectroscopy is performed under various conditions of water impregnation, electric field and temperature. A very large increase of permittivity and losses is recorded in the presence of water, especially at low frequency. At power frequency, dielectric properties do not show a non-linearity when the field is increased up to service values. At very low frequency, a decrease of losses when the fields is increased is observed. It is due to the Garton effect. Most of results show that the wet material behaves as a low frequency dispersion system (LFD). [ABSTRACT FROM AUTHOR]

A new method for quantitative "reading" of dielectric data of two-phase dielectric mixtures is suggested. This method is based on ideas related to the application of the generalized mean value (GMV) function to random data series (statistics of fractional moments). The GMV function allows transformation of arbitrary random data series to smooth curves that in turn can be fitted by an analytical function with a limited number of parameters. These fitting parameters are sensitive to the influence of an external factor, so the dependence of these parameters on the external factor can be used as calibration curves. In this instance we analyzed dielectric data measured for ground hard red winter wheat with 12.5%, 17.9% and 21.2% moisture contents in the temperature range from 2 °C to 76 °C. This system is a complex system from the viewpoint of the complexity of the dielectric data interpretation. The common treatment of these dielectric spectra does not provide a monotonic calibration curve. We treated these spectra as random data series by the use of the GMV function. As a result of this treatment, we obtained the monotonic temperature dependence of several fitting parameters for the given moisture contents, and these relationships can be fitted by an analytical function for calibration use. We hope that this new method will find application for analysis of other complex systems. [ABSTRACT FROM AUTHOR]

For reliable operation of power transformers, the condition of the insulation system is essential. This paper reports on a detailed study of the effect of ageing, temperature and moisture on frequency and time domain spectroscopic measurements carried out on oil-impregnated pressboard samples as well as on a distribution transformer under controlled laboratory conditions. Because field measurements are generally performed after dc-energizing the transformer, extreme care is required in interpreting the results due to inherent temperature instabilities. To avoid large thermal variations that may affect the results, a customized adiabatic room was built around the transformer for measurements above the ambient. Capacitance ratio and direct current conductivity deduced from the spectroscopic measurements, helped to interpret the data. Because, low frequency measurements techniques are time consuming, alternative to a transfer of time domain data into frequency domain data was investigated. [ABSTRACT FROM AUTHOR]

In order to understand the relationship between the dielectric properties and the structure of polymer nanocomposites, especially the role of the interface on dielectric response, two polymers with different polarity were used to form nanocomposites with nanoalumina powder, a typical polar inorganic compound. Consequently, two kinds of nanodielectrics with very different interfaces were produced. In the epoxy nanodielectric, broad band dielectric spectroscopic measurements show that no difference is found between the unfilled resin and the nano composite under dry conditions. However, their dielectric responses are very different when they contain about 0.4 % b.w. absorbed water, a concentration that occurs under ambient exposure conditions. The findings suggest that the sites for absorbed water in the epoxy nanocomposites are very different to those in the unfilled thermoset and relate to the large interfacial internal surface in these materials. In this case all the relaxation processes can be well described by the Havriliak-Negami function, which give useful information on the dynamics and activation energies associated with the relaxation processes. In polyethylene nanocomposites, dielectric measurements show that the incorporation of nanoalumina produces a dielectric loss peak in the low frequency. This relaxation peak moves to high frequency with increasing nanoalumina content and the peak becomes broader. In the presence of 0.06 % b.w. absorbed water this peak also shows the same type of unusual dielectric loss behavior as that observed in the undried epoxy nanodielectrics. This behavior is thought to arise from the interplay between interfacial water mobility and bonding rather than the host polymer. [ABSTRACT FROM AUTHOR]

In this research, the influence of water absorption on the dielectric properties of epoxy resin and epoxy micro-composites and nano-composites filled with silica has been studied. Nanocomposites were found to absorb significantly more water than unfilled epoxy. However, the microcomposite absorbed less water than unfilled epoxy: corresponding to the reduced proportion of the epoxy in this composite. The glass transition temperatures (Tg) of all the samples were measured by both differential scanning calorimetry and dielectric spectroscopy. The Tg decreased as the water absorption increased and, in all cases, corresponded to a drop of approximately 20 K as the humidity was increased from 0% to 100%. This implied that for all the samples, the amount of water in the resin component of the composites was almost identical. It was concluded that the extra water found in the nanocomposites was located around the surface of the nanoparticles. This was confirmed by measuring the water uptake, and the swelling and density change, as a function of humidity as water was absorbed. The water shell model, originally proposed by Lewis and developed by Tanaka, has been further developed to explain low frequency dielectric spectroscopy results in which percolation of charge carriers through overlapping water shells was shown to occur. This has been discussed in terms of a percolation model. At 100% relative humidity, water is believed to surround the nanoparticles with a thickness of approximately 5 monolayers. A second layer of water is proposed that is dispersed but sufficiently concentrated to be conductive; this may extend for approximately 25 nm. If all the water had existed in a single layer surrounding a nanoparticle, this layer would have been approximately 3 to 4 nm thick at 100%. This "characteristic thickness" of water surrounding a given size of nanoparticle appeared to be independent of the concentration of nanoparticles but approximately proportional to water uptake. Filler particles that have surfaces that are functionalized to be hydrophobic considerably reduce the amount of water absorbed in nanocomposites under the same conditions of humidity. Comments are made on the possible effect on electrical aging. [ABSTRACT FROM AUTHOR]

Condition monitoring of different power equipment with noninvasive and nondestructive techniques, such as Dielectric Spectroscopy, has become one of the important facets of power system reliability. This is increasingly becoming essential for predicting the insulation condition and probable future failure of power apparatus. Noise contamination, being one of the major problems in these measurements, should be treated judiciously. The paper proposes a simple but versatile real-time denoising scheme for this kind of signals of Dielectric spectroscopy in time domain namely, Polarization-Depolarization Current (PDC) and Recovery Voltage (RV), through a hybrid filtering technique using weighted median (WM) filter along with low pass digital infinite impulse response (IIR) filter. The proposed filter is able to remove real- life, random, high frequency noises as well as spurious impulse signals while preserving any step change in the signal. The performance of the proposed scheme is judged through experimentation using a real-time, automated computer controlled test setup for condition monitoring of transformers and the results show that it performs efficiently on different types of signals of dielectric spectroscopy in time domain, namely, PDC and RV. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy data from measurements on four insect species from 200 MHz to 20 GHz over a temperature range from 10 to 70 °C are described through reduction of numerous micromotions to a few collective motions, recognition of a low-frequency dispersion through ratio presentation format, application of a self-consistent iteration procedure, a separation procedure for types of collective motions, and application of the eigen-coordinates method for calculation of seven fitting parameters, Use of such fitting parameters to describe the total system relaxation processes quantitatively should enable practical uses of dielectric spectroscopy for measuring desired qualities or characteristics of biological and other complex materials. This general approach based on the reduction procedure and the use of different formats, including the original fitting procedure, allows more precise determination of the corresponding fitting function and description of dielectric spectra of complex systems. The application of this general methodology can be considered as the basic goal and motivation for this paper. [ABSTRACT FROM AUTHOR]

The temperature dependent dielectric spectroscopy in frequency domain is compared to physicochemical and electrical tests that are periodically applied on highly insulating transformer oils. Complex permittivity and tans data are obtained as a function of frequency and operation temperatures, to demonstrate the polarization phenomena and the induced loss intensification by the thermally stimulated currents. The acquired dielectric data of oil samples collected from 201 operating High Voltage (HV) power transformers, were correlated to their corresponding physicochemical ones in order to demonstrate the future potential employment of the proposed measuring technique in the field of high voltage engineering, towards reliability monitoring of oil filled electrical equipment (OFEE). [ABSTRACT FROM AUTHOR]

This paper points out the advantages offered by the temperature dependent dielectric spectroscopy in frequency domain, as an additional diagnostic technique for insulation testing of power transformers for life-time prediction. Complex permittivity measurements have been carried out as a function of operating frequency and oil temperature for a wide selection of high voltage transformers and the gaseous byproduct concentrations were also monitored. The work correlates dielectrometry data to the gas chromatography ones. [ABSTRACT FROM AUTHOR]

This paper presents the electrical characterization of antimony-doped semiconducting glazes before and after exposure to ac and dc electric fields under outdoor conditions and In the laboratory using the rotatlng-wheel-dip test (RWDT). Measurements of the I-V characteristics as well as dielectric spectroscopy in frequency domain (EDS) were performed on new and aged samples and results were compared. While I-V data only show a decrease in the current with aging, FDS data show more detailed features. Besides a decrease in dc conductance, a strong increase in low frequency dispersion (LFD) was found and a decrease in the relaxation polarization was indicated. The tatter was more pronounced for samples aged under dc voltage. The observed relaxation polarization could originate from the presence of a low-conductive glassy surface layer on top of the "bulk" semiconducting glaze and it was weakened by the appearance of surface changes, including damage of the glassy surface layer, which thereby opened an alternative path for the current flow from the electrode to the "bulk" semiconducting glaze. The increase in LFD could be attributed to moisture trapped in the surface cracks formed during aging. [ABSTRACT FROM AUTHOR]

The origin of polarization phenomena occurring in amorphous polymers has been investigated, using dielectric dynamic spectroscopy and thermo stimulated current analysis. Linear polymers, e.g. poly(methyl methacrylates) and poly(ethyl methacrylates), show a molecular mobility which is increasingly delocalised along the backbone with increasing temperature. Dendrimers with a phosphorus core and increasingly complex radial branches showed a hierarchy of molecular mobility as a function of generation. [ABSTRACT FROM AUTHOR]

In many items of high voltage plant, a mineral or synthetic oil is used in conjunction with paper as the dielectric medium. However, increasing awareness of the environmental impact of human activity and increasing disposal costs have encouraged researchers to direct their attention to renewable and biodegradable alternatives. Originally used in capacitors, vegetable oils are now finding widespread use in some transformer installations, particularly in the United States. Therefore, it seems prudent to begin systematic investigations of the aging behavior of a number of vegetable based oils and assess their potential for application in high voltage systems. A total of five food grade vegetable oils, an oil specifically formulated for high voltage applications (Envirotemp FR3) and dodecylbenzene (DDB) were aged at various temperatures in air. Their aging behavior was assessed by ultra-violet/visible, infrared and dielectric spectroscopies supplemented with measurements of viscosity. It was found that olive oil offered excellent resistance to aging (comparable to Envirotemp oil), rapeseed oil offered intermediate properties whereas corn and sunflower oil oxidized appreciably after aging. Despite being more prone to oxidation, all the vegetable oils offered dielectric properties which were better than dodecylbenzene and similar to mineral oil. [ABSTRACT FROM AUTHOR]

In this work we have proposed a combined experimental-numerical technique to elicit important quantitative information about the dielectric properties of the interphase region surrounding a nanoparticle embedded in a polymer matrix. The method involves performing permittivity measurements through dielectric spectroscopy and combining with concurrent unit cell based Finite Element solutions of the electrostatic fields. The analysis has to be supplemented with some information about the degree of agglomeration in the nanocomposites which are estimated from electron microscopy done at several resolutions. For an epoxy matrix with 40 nm alumina nanoparticles, our analysis indicates the presence of an interphase region about 200 nm thick and having permittivity lower than that of epoxy. Heating the nanoparticles prior to the synthesis of the nanocomposite makes the interphase region thicker and lowers its permittivity slightly. At higher volume fractions of the nanoparticles, agglomeration sets in and creates regions of even higher volume fraction within the matrix. Our analysis also revealed that at 2% volume fraction of alumina nanoparticles, 600 nm sized agglomerates exist in the matrix leading to local particle volume fraction as high as 5%. [ABSTRACT FROM AUTHOR]