Showing papers on "Insulator (electricity) published in 2010"
TL;DR: In this paper, it was shown that the magnetic insulator LaY(2)Fe(5)O(12) can convert a heat flow into a spin voltage, which can then be converted into an electric voltage as a result of the inverse spin Hall effect.
Abstract: Thermoelectric generation is an essential function in future energy-saving technologies. However, it has so far been an exclusive feature of electric conductors, a situation which limits its application; conduction electrons are often problematic in the thermal design of devices. Here we report electric voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, the magnetic insulator LaY(2)Fe(5)O(12) can convert a heat flow into a spin voltage. Attached Pt films can then transform this spin voltage into an electric voltage as a result of the inverse spin Hall effect. The experimental results require us to introduce a thermally activated interface spin exchange between LaY(2)Fe(5)O(12) and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect.
1,011 citations
TL;DR: Electronic transport measurements on thin Bi2Se3 devices are reported and it is shown that the density of the surface states can be modulated via the electric field effect by using a top-gate with a high-k dielectric insulator.
Abstract: Electronic transport experiments involving the topologically protected states found at the surface of Bi2Se3 and other topological insulators require fine control over carrier density, which is challenging with existing bulk-doped material. Here we report on electronic transport measurements on thin (<100 nm) Bi2Se3 devices and show that the density of the surface states can be modulated via the electric field effect by using a top-gate with a high-k dielectric insulator. The conductance dependence on geometry, gate voltage, and temperature all indicate that transport is governed by parallel surface and bulk contributions. Moreover, the conductance dependence on top-gate voltage is ambipolar, consistent with tuning between electrons and hole carriers at the surface.
258 citations
TL;DR: In this paper, a top-gate with a high-k dielectric insulator was used to modulate the surface states of Bi2Se3 and showed that the density of surface states can be modulated via the electric field effect.
Abstract: Electronic transport experiments involving the topologically protected states found at the surface of Bi2Se3 and other topological insulators require fine control over carrier density, which is challenging with existing bulk-doped material. Here we report on electronic transport measurements on thin (<100 nm) Bi2Se3 devices and show that the density of the surface states can be modulated via the electric field effect by using a top-gate with a high-k dielectric insulator. The conductance dependence on geometry, gate voltage, and temperature all indicate that transport is governed by parallel surface and bulk contributions. Moreover, the conductance dependence on top-gate voltage is ambipolar, consistent with tuning between electrons and hole carriers at the surface.
246 citations
01 Nov 2010
TL;DR: In this paper, a top-gate with a high-k dielectric insulator was used to modulate the surface states of Bi2Se3 and showed that the density of surface states can be modulated via the electric field effect.
Abstract: Electronic transport experiments involving the topologically protected states found at the surface of Bi2Se3 and other topological insulators require fine control over carrier density, which is challenging with existing bulk-doped material. Here we report on electronic transport measurements on thin (<100 nm) Bi2Se3 devices and show that the density of the surface states can be modulated via the electric field effect by using a top-gate with a high-k dielectric insulator. The conductance dependence on geometry, gate voltage, and temperature all indicate that transport is governed by parallel surface and bulk contributions. Moreover, the conductance dependence on top-gate voltage is ambipolar, consistent with tuning between electrons and hole carriers at the surface.
206 citations
TL;DR: A low voltage, two-level-metal, and multi-layer insulator electrowetting-on-dielectric (EWD) platform, which enables the fabrication of smaller and denser electrodes with high interconnect routing flexibility and achieves low dispensing and actuation voltages for scaled devices with 30pl droplets.
Abstract: A low voltage, two-level-metal, and multi-layer insulator electrowetting-on-dielectric (EWD) platform is presented. Dispensing 300pl droplets from 140nl closed on-chip reservoirs was accomplished with as little as 11.4V solely through EWD forces, and the actuation threshold voltage was 7.2V with a 1Hz voltage switching rate between electrodes. EWD devices were fabricated with a multilayer insulator consisting of 135nm sputtered tantalum pentoxide (Ta(2)O(5)) and 180nm parylene C coated with 70nm of CYTOP. Furthermore, the minimum actuation threshold voltage followed a previously published scaling model for the threshold voltage, V(T), which is proportional to (t/e(r))(1/2), where t and e(r) are the insulator thickness and dielectric constant respectively. Device threshold voltages are compared for several insulator thicknesses (200nm, 500nm, and 1µm), different dielectric materials (parylene C and tantalum pentoxide), and homogeneous versus heterogeneous compositions. Additionally, we used a two-level-metal fabrication process, which enables the fabrication of smaller and denser electrodes with high interconnect routing flexibility. We also have achieved low dispensing and actuation voltages for scaled devices with 30pl droplets.
162 citations
IBM1
TL;DR: It is shown that silicon nitride can provide uniform coverage of graphene in field-effect transistors while preserving the channel mobility and the field-induced band gap or band overlap in the different layers.
Abstract: We show that silicon nitride can provide uniform coverage of graphene in field-effect transistors while preserving the channel mobility. This insulator allowed us to study the maximum channel resistance at the Dirac (neutrality) point as a function of the strength of a perpendicular electric field in top-gated devices with different numbers of graphene layers. Using a simple model to account for surface potential variations (electron-hole puddles) near the Dirac point we estimate the field-induced band gap or band overlap in the different layers.
161 citations
TL;DR: It is found that electric fields as low as 2 kV/cm induce an electronic phase change in these compounds from a Mott insulating state to a metallic-like state, suggesting that this transition belongs to a new class of resistive switching.
Abstract: The fundamental building blocks of modern silicon-based microelectronics, such as double gate transistors in non-volatile Flash memories, are based on the control of electrical resistance by electrostatic charging. Flash memories could soon reach their miniaturization limits mostly because reliably keeping enough electrons in an always smaller cell size will become increasingly difficult . The control of electrical resistance at the nanometer scale therefore requires new concepts, and the ultimate resistance-change device is believed to exploit a purely electronic phase change such as the Mott insulator to insulator transition [2]. Here we show that application of short electric pulses allows to switch back and forth between an initial high-resistance insulating state ("0" state) and a low-resistance "metallic" state ("1" state) in the whole class of Mott Insulator compounds AM4X8 (A = Ga, Ge; M= V, Nb, Ta; X = S, Se). We found that electric fields as low as 2 kV/cm induce an electronic phase change in these compounds from a Mott insulating state to a metallic-like state. Our results suggest that this transition belongs to a new class of resistive switching and might be explained by recent theoretical works predicting that an insulator to metal transition can be achieved by a simple electric field in a Mott Insulator. This new type of resistive switching has potential to build up a new class of Resistive Random Access Memory (RRAM) with fast writing/erasing times (50 ns to 10 μs) and resistance ratios ΔR/R of the order of 25% at room temperature.
130 citations
TL;DR: In this paper, the performance of silicone rubber composite and hybrid silicone-ceramic insulators was evaluated in laboratory by measurements of leakage currents under clean fog conditions and of wet flashover voltage.
Abstract: This paper presents investigations on the performance of 33 kV silicone rubber insulators characterized by different creepage lengths, which aimed to find out whether the insulators could permanently work when electrically stressed beyond the recommended limits in polluted and clean tropical environments. The study was performed under natural field and laboratory conditions. The insulators tested included eight types of silicone rubber composite insulators, one type of hybrid silicone-ceramic insulator and one semi-conducting glazed porcelain insulator, while ordinary porcelain and glass insulators were used as reference. During the field investigation, two sets of the insulators were separately installed and energized in coastal and inland parts of Sri Lanka, being by that exposed to marine and clean tropical environments. Their performances were periodically evaluated by visual inspections and measurements of hydrophobicity class. After five years of field exposure, the insulator performances were evaluated in laboratory by measurements of leakage currents under clean fog conditions and of wet flashover voltage. A third set of the insulators was aged in laboratory for 1000 hours inside a salt fog chamber where the insulators were continuously energized and daily sprayed with salt solution for eight hours and left to rest for remaining 16 hours. This treatment represented conditions similar as those in the field i.e. insulators exposed to salt sprays during monsoons. The insulator performances were investigated by measurements of leakage currents and classifying their patterns into different categories, i.e. capacitive, resistive, non-linear, discharge and strong discharge types, by means of fast Fourier transform and short time Fourier transform analyses. It was found that the long-term field exposure yielded weaker insulator deterioration than the salt fog chamber ageing, which indicated for a possibility to increase the electric stress on silicone rubber insulators to levels higher than the ones used today on glass and porcelain counterparts.
102 citations
TL;DR: In this article, the impact of non-uniform pollution carried out under 50 Hz applied voltage on a plane model simulating the 1512 L outdoor insulator largely used by the Algerian Company of Gas and Electric Power (SONELGAZ).
Abstract: In this paper, we present results dealing with the non-uniform pollution carried out under 50 Hz applied voltage on a plane model simulating the 1512 L outdoor insulator largely used by the Algerian Company of Gas and Electric Power (SONELGAZ). Many configurations in non-uniform pollution are studied in the ENP's (Ecole Nationale Polytechnique d'Alger) High Voltage Laboratory in order to analyze the impact of polluted layer distribution on the insulator dielectric performances. The polluted solution has a conductivity of 1.2 mS/cm obtained with distilled water and NaCl. Our investigations are particularly focused on the on line monitoring of both position and width of the contaminated layer. The flashover voltage and the leakage current magnitude have been investigated in order to study the flashover process on this insulating surface. A video apparatus is used to reflect the parallel discharges behavior, appearing when the polluted layer reaches a critical width. Phase angle values between applied voltage and leakage current (LC) signals at the fundamental frequency (50 Hz) are calculated using the Fast Fourier Transform (FFT) spectral analysis. Phase angle measurements indicate that the equivalent impedance of the insulator behaves like RC circuit with a high capacitive effect engendered by the pre-established clean band. This effect decreases when electric discharges occur at a particular voltage level. The Discrete Wavelet Transform (DWT) is adopted for the leakage current decomposition in several time-frequency bands. The STD-MRA (Standard deviation-Multi Resolution Analysis) of these frequency bands is calculated and is employed to choose the most interesting details that detect both position and width increasing of the conducting layer. Reported results show that the pollution surface state and the severity of this conducting layer deposited on insulator surface could be identified from the STD-MRA representation of leakage current frequency bands. It was shown that the high frequency band of the leakage current increases before the final flashover when the polluted layer is located in the middle of the plane model. It was established that a good correlation has been found between the insulator state surface and details of the leakage current obtained through the DWT decomposition. In fact, these details provide relevant information on both position and width of the polluted layer nonuniformly distributed on the insulator surface.
94 citations
TL;DR: In this paper, the role of electrical charge transport and trapping in alumina ceramics on their resistance to dielectric breakdown is studied in polycrystalline materials, where the interfaces between the various phases play a main role because they constitute potential sites for the trapping of electrical charges.
Abstract: Dielectric breakdown constitutes an important limitation in the use of insulating materials under high-voltage since it can lead to the local fusion and sublimation of the insulator. The role of electrical charge transport and trapping in alumina ceramics on their resistance to this catastrophic phenomenon is studied in this work. In polycrystalline materials, the interfaces between the various phases play a main role because they constitute potential sites for the trapping of electrical charges. The density and the nature of these interfaces can be controlled by the way of the microstructure parameters. So, the aim of the present paper is to highlight the influence of average grain size and intergranular phase crystallization rate on the ability of polycrystalline alumina materials to resist to dielectric breakdown. Thus, it is shown that the control of the process conditions (sintering aids content, powder grain size and thermal cycle) makes it possible to change not only the density (by the average grain size) but also the nature (by the crystallization or not of anorthite) of the grain boundaries. On one hand, at room temperature a high density of interfaces, due to low grain size and highly crystallized intergranular phase, leads to a high dielectric strength. On the other hand, at higher temperature (250 °C), the presence of vitreous intergranular phase makes it possible to delay breakdown. That behaviour is explained thanks to charge transport and trapping characterizations.
85 citations
TL;DR: It is revealed that, despite the absence of conduction electrons, the magnetic insulator LaY(2)Fe(5)O(12) can convert a heat flow into a spin voltage, which can be converted into an electric voltage as a result of the inverse spin Hall effect.
Abstract: Thermoelectric generation is an essential function of future energy-saving technologies. However, this generation has been an exclusive feature of electric conductors, a situation which inflicts a heavy toll on its application; a conduction electron often becomes a nuisance in thermal design of devices. Here we report electric-voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, a magnetic insulator LaY2Fe5O12 converts a heat flow into spin voltage. Attached Pt films transform this spin voltage into electric voltage by the inverse spin Hall effect. The experimental results require us to introduce thermally activated interface spin exchange between LaY2Fe5O12 and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect.
Patent•
IBM1
TL;DR: In this paper, a through-silicon via (TSV) structure forming a unique coaxial or triaxial interconnect within the silicon substrate is described, which is provided with two or more independent electrical conductors insulated from another and from the substrate.
Abstract: A through-silicon via (TSV) structure forming a unique coaxial or triaxial interconnect within the silicon substrate. The TSV structure is provided with two or more independent electrical conductors insulated from another and from the substrate. The electrical conductors can be connected to different voltages or ground, making it possible to operate the TSV structure as a coaxial or triaxial device. Multiple layers using various insulator materials can be used as insulator, wherein the layers are selected based on dielectric properties, fill properties, interfacial adhesion, CTE match, and the like. The TSV structure overcomes defects in the outer insulation layer that may lead to leakage. A method of fabricating such a TSV structure is also described.
TL;DR: It is demonstrated that water-infiltrated nanoporous glass electrically switches an oxide semiconductor from insulator to metal, which exhibits exotic thermoelectric behaviour.
Abstract: Water is composed of two strong electrochemically active agents, H+ and OH− ions, but has not been used as an active electronic material in oxide semiconductors In this study, we demonstrate that water-infiltrated nanoporous glass electrically switches an oxide semiconductor from insulator to metal We fabricated a field-effect transistor structure on an oxide semiconductor, SrTiO3, using water-infiltrated nanoporous glass—amorphous 12CaO·7Al2O3—as the gate insulator Positive gate voltage, electron accumulation, water electrolysis and electrochemical reduction occur successively on the SrTiO3 surface at room temperature This leads to the formation of a thin (~3 nm) metal layer with an extremely high electron concentration (1015–1016 cm−2), which exhibits exotic thermoelectric behaviour The electron activity of water as it infiltrates nanoporous glass may find many useful applications in electronics or in energy storage Water is composed of the electrochemically active species, H+ and OH−, but has not been used as an active electronic material In this study, a field-effect transistor is developed that uses water-infiltrated nanoporous glass as the gate insulator; this new application of water may be useful in electronics and energy storage
TL;DR: In this paper, the electrical and material characteristics of field-aged silicone rubber composite insulators have been investigated on a 400 kV transmission line in a coastal region of the UK.
Abstract: This paper presents the electrical and material characteristics of field-aged silicone rubber composite insulators, which have been deployed for 15 years on a 400 kV transmission line in a coastal region of the UK. There were no indications of reduced performance in service. Observations indicate non-uniform aging of the insulators on the different surfaces of the insulator sheds and core, along the insulator string length and in the different compass orientations. A uniquely large number of contact angle measurements, made on each of the insulators' different surfaces, confirm the visual aspect of nonuniform aging. Electrical investigations of the insulators have been performed in terms of leakage current analysis, ac flashover / withstand and switching-surge impulse flashover. A correlation is seen between the ac leakage current and the hydrophobicity measurements. Energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) analysis of the changes of the materials' surface chemistry is presented. The role of solar radiation and organic growth appears critical to the observed non-uniform aging and must be considered if the longer term operation of the insulator is to be forecast. It is proposed that a reduction of the difference between positive and negative wet-flashover voltages may be a good indicator of early insulator aging.
TL;DR: In this article, the Inclined Plane Test (IPT) method was used to evaluate the performance of different materials when energized by ac and dc (both polarities) voltages.
Abstract: An experimental study was conducted, using the Inclined Plane Test method to determine the performance of typical power line insulator materials: RTV (Room Temperature Vulcanized) silicone rubber coated porcelain, HTV (High Temperature Vulcanized) silicone rubber and EPDM rubber. The constant voltage method was employed to evaluate the performance of the above samples when energized by ac and dc (both polarities) voltages. The relative performance of the different materials and the effect of the voltage types were investigated. The results show that the RTV silicone rubber coating exhibits the least erosion for ac voltage but shows extensive erosion in the case of negative dc voltage. The HTV silicone rubbers exhibit only minimal erosion when exposed to ac test voltage, but develop strong erosion under positive dc voltage, which can result in sample failure. EPDM experiences the least erosion for a negative dc voltage, but shows maximum erosion severity for ac voltage.
TL;DR: In this paper, the III-V-OI n-channel metal-insulator-semiconductor field effect transistors under the back-gate configuration showed the peak mobility of 1800 cm2/V
Abstract: We have developed III-V-semiconductor-on-insulator (III-V-OI) structures on Si wafers with excellent bottom interfaces between In0.53Ga0.47As-OI channel layers and atomic-layer-deposited Al2O3 (ALD-Al2O3) buried oxides (BOXs). A surface activated bonding process and the sulfur passivation pretreatment have realized the excellent In0.53Ga0.47As-OI/ALD-Al2O3 BOX bottom interface properties. As a result, the III-V-OI n-channel metal-insulator-semiconductor field-effect transistors under the back-gate configuration showed the peak mobility of 1800 cm2/V s and the higher electron mobility than the Si universal one even in the high effective electric field range because of the reduction in the surface roughness and fixed charges.
TL;DR: In this article, the influence of non-uniform pollution distribution on DC composite insulators on their flashover performance was analyzed, and a correction formula for the non uniform pollution flashover voltage was proposed, based on artificial pollution tests carried out on short samples of a composite insulator intended for ±800 kV UHVDC.
Abstract: Differences in the amount of pollution on the top and bottom surfaces of an insulator have a great influence on the DC pollution flashover voltage. Up to now, many investigations have been carried out on non-uniform pollution flashover performance of porcelain and glass insulators, but very few on composite insulators. In this paper the influence of non-uniform pollution distribution on DC composite insulators on their flashover performance was analyzed, and a correction formula for the non-uniform pollution flashover voltage was proposed, based on artificial pollution tests carried out on short samples of a composite insulator intended for ±800 kV UHVDC. The test results showed that, when the ratio (T/B) of the salt deposit density (SDD) on the top surface to that on the bottom surface is between 1/1 and 1/10, the value of the characteristic exponent a indicating the effect of SDD on the flashover voltage ranges from 0.22 to 0.255. The value of a is nearly independent of T/B. However, the flashover voltage U50 decreases with the increase in T/B. The correction formula indicating the influence of non-uniform pollution distribution on the flashover voltage could be expressed as K=1 - b×log(T/B). For the tested composite insulators, the factor b was 0.141 to 0.156, which is smaller than that of porcelain or glass insulator. That is to say, the influence of T/B on the flashover voltage of the composite insulator is weaker than those on the porcelain and glass insulators.
TL;DR: In this paper, the authors used a recurrent plot approach to determine the flashover performance of rime-iced composite insulator, where the high frequency components were extracted by using a wavelet transform technique.
Abstract: Due to the wide application of composite insulators in the power industry, the insulator performance is challenged by various environments To determine the flashover performance of rime-iced composite insulator, laboratory investigation was carried out in an artificial climate chamber to simulate different rime-ice morphology on the insulator surface The configuration and characteristics of the rime-ice were demonstrated to establish the relationship between the rime-ice parameters and the flashover performance In accordance with the discharge phenomena, the transition of leakage current (LC) until the flashover was analyzed by using a recurrent plot approach After extracting the high frequency components by using a wavelet transform technique, the LC just before the flashover was extended to m dimensional phase space based on a phase space reconstructed method The recurrent plot was obtained to reveal the non-linear characteristics of LC for identifying the dynamic behaviors on the insulator surface It is shown that the propagation and properties of the discharges can be graphically projected on the topological structure of recurrent plot as a function of the rime-ice parameters The process and underlying mechanism of flashover performance of rime-iced composite insulator can be visually reflected by the recurrent plot and the quantitative indicators of LC
TL;DR: In this article, the authors studied the charge transportation in poly(3-butylthiophene) (P3BT)/insulating polymer composites both microscopically and macroscopically.
Abstract: The charge transportation in poly(3-butylthiophene) (P3BT)/insulating polymer composites is studied both microscopically and macroscopically. The increased mobility of free charge carriers, in particular hole mobility, contributes to the enhanced electrical conductivity of this semiconductor/insulator composite. The conductivity origin of the composite, as revealed by conductive-atomic force microscopy (C-AFM), comes mainly from the P3BT network, whose carrier mobility has been improved as a result of reduced activation energy for charge transportation upon forming an interface with the insulating matrix. Both the huge interfacial area and interconnected conductive component are morphologically required for the enhanced electrical property of the composite. An increased size of the P3BT domains, which correspondingly reduces the interfacial area between the two components, ruins the enhancement. This study clarifies the mechanism of the higher electrical properties achieved in a semiconducting polymer upon blending with an insulating polymer, which will further promote the development of these low-cost, easily processable, and environmentally stable composites.
TL;DR: In this paper, a spin-polarized photoelectron gun was constructed that employs a compact inverted-geometry ceramic insulator for dc high voltage spinpolarization.
Abstract: A new dc high voltage spin-polarized photoelectron gun has been constructed that employs a compact inverted-geometry ceramic insulator. Photogun performance at 100 kV bias voltage is summarized.
TL;DR: In this paper, the effect of non-uniform pollution on the electrical performance of 14-unit standard XP-70 ceramic insulators for 220-kV transmission lines is investigated.
Abstract: Pollution flashover of line insulators may cause regional accidents. Research on the effect of non-uniform pollution on the electrical performance of insulators is important for the outdoor insulation coordination. A study on the effect of the non-uniform pollution distribution on the withstand characteristics of an insulator string with 14-unit standard XP-70 ceramic insulators for 220 kV transmission lines is presented. Test results show that ρESDD, N and T/B have their own effects on the withstand voltage of polluted insulator string. And their effects are independent from each other. The withstand voltage of the insulator string increases with the decrease of T/B. By regressing the test results, the relationship between the withstand voltage of 14-unit XP-70 insulator and ρESDD, N as well as T/B is obtained, which can be used in the outdoor insulation coordination of transmission lines. Moreover, the mechanism of the effect of non-uniform pollution distribution on the withstand voltage is analysed. The non-uniform pollution distribution along the insulator surface causes the decrease of the equivalent surface conductivity and the difference of the hydroscopicity between the top and the bottom surfaces, which results in the increase of the withstand voltage and the decrease of the mean root-mean-square value of leakage current.
TL;DR: In this paper, the effect of pre-deposited surface charges on impulse flashover characteristics of a polymeric insulator is studied by means of computer simulations utilizing a model based on criteria for streamer inception, propagation and sustenance.
Abstract: Effect of pre-deposited surface charges on impulse flashover characteristics of a polymeric insulator is studied by means of computer simulations utilizing a model based on criteria for streamer inception, propagation and sustenance. A parametric study is performed to investigate the influences imposed by magnitude and polarity of the charge, its location on insulator surface and properties of insulator material on its flashover voltages. The obtained results are analyzed in terms of electric field distributions in the vicinity of the insulator surface and are compared with experimental data available in the literature.
TL;DR: In this article, the leakage current harmonic components of 45 glass insulator samples were investigated and the results indicated that the insulator sample's leakage current waveform and the total harmonic distortion correspond well with degree of ageing.
Abstract: This paper reports an investigation into the leakage current harmonic components of 45 units of glass insulator samples. The insulator units comprise 5 groups of insulators: new insulators and naturally field-aged insulators with different ageing periods->30, 20, 15, and <;10 years from a 132 kV transmission line. Experiments were conducted at different electrical stresses (0.17, 0.24, and 0.34 kV/cm) and salt-fog conductivities (900 and 1500 μS/cm). The results suggest that the insulator samples' leakage current (LC) waveform and the total harmonic distortion (THD) correspond well with degree of ageing. Fast Fourier Transform (FFT) analysis performed on the stored waveforms showed a strong correlation between the ratio of the third to fifth harmonic amplitudes with the degree of ageing and in-service period of the naturally field-aged insulators. Furthermore, this investigation revealed a pattern between the groups of insulator samples in respect to their ageing. These findings were further validated with traditional Dielectric Dissipation Factor tests carried out on the insulators, and the results also correlated well with the samples' degree of ageing as well as service period. In addition, neural networks were trained to recognize the insulator samples' degree of ageing. This study found that, alternative to the diagnosis of insulator ageing through the measurement of loss angles or tangent delta, LC harmonics can be used as diagnostic tools and for the on-line monitoring of in-service aged transmission line ceramic glass insulators based on odd harmonics and third to fifth harmonic ratios.
TL;DR: The collection of sub-100 nm electrospun poly(lactic acid-co-glycolic acid) nanofibers with a good degree of alignment is found to require intermediate size gaps of high resistivity, to enhance the spatial extent of stretching forces while maintaining the dominance of repulsive forces due to residual charge across a majority of the temporal extent of the gap.
Abstract: We present a quantitative design methodology for optimizing insulator gap width, gap resistivity, and collector to needle height for the alignment of sub-100 nm electrospun nanofibers at insulator ...
TL;DR: In this paper, the authors investigated the dc pollution flashover performance of various types of porcelain, glass, and composite insulators and presented analysis of the dc flashover process of polluted insulator string at high altitude using insight from high-speed photography.
Abstract: In this paper, the dc pollution flashover performance of various types of porcelain, glass, and composite insulators is investigated. It also presents analysis of the dc flashover process of polluted insulator string at high altitude using insight from high-speed photography. The research results indicate that the relationship between the dc pollution flashover voltage and the string length of insulators is basically linear, the characteristic exponents describing the influence degree of air pressure on pollution flashover voltage vary between 0.35 and 0.77 and are related to the insulator types and pollution degree, etc., the characteristic exponents describing the influence degree of pollution on flashover voltage vary between 0.24 and 0.36 and are related to the insulator types and air pressure, etc. Based on the flashover phenomena using the insight from high-speed photography, a new physical model explaining the flashover mechanism for a polluted insulator string at high altitude is introduced, which can be expressed as an electrical circuit consisting of a surface arc of length x1 and air-gap arc of length x2 in series with a resistance representing the wet pollution layer. In addition, the exponent n describing the influence degree of air pressure on flashover voltage for the polluted insulator is discussed.
TL;DR: In this paper, the issue of serious insulator string partial discharge activity and flashover resulted from severe contaminant accumulation of insulators on a 220 kV transmission line in coastal areas during winter when the rain is sparse and heavy contamination accumulates over time.
Abstract: This paper attempts to address the issue of serious insulator string partial discharge activity and flashover resulted from severe contaminant accumulation of insulators on a 220 kV transmission line in coastal areas during winter when the rain is sparse and heavy contamination accumulates over time. Samples of silicone composite insulators, glass insulator with RTV coating and ceramic station insulator are tested in a series of experiments including ESDD and NSDD measurement, hydrophobicity classification, the measurement of static contact angle, TGA and FTIR analysis. Taking the terrain of the transmission line into consideration, it probes into the mechanism of contaminant accumulation and flashover of insulators in heavily polluted coastal areas. A conclusion has been made that the high salt deposit on the surface of the insulators resulted from peculiar terrain and the dampening effect on hydrophobicity transfer characteristic of silicone composite material lower the flashover voltage of silicone composite insulators and ceramic or glass insulators with RTV coatings leading to severe partial discharge activity and flashovers during dry winter. Finally it sums up the lessons in regards to this problem and proposes appropriate solutions.
TL;DR: Experimental results demonstrated that this novel dielectrophoretic mode allows highly controlled particle manipulation.
Abstract: Low frequency alternating current insulator-based dielectrophoresis is a novel technique that allows for highly controlled manipulation of particles. By varying the shape of an AC voltage applied across a microchannel containing an array of insulating cylindrical structures it was possible to concentrate and immobilize microparticles in bands; and then, move the bands of particles to a different location. Mathematical modeling was performed to analyze the distribution of the electric field and electric field gradient as function of the shape of the AC applied potential, employing frequencies in the 0.2–1.25 Hz range. Three different signals were tested: sinusoidal, half sinusoidal and sawtooth. Experimental results demonstrated that this novel dielectrophoretic mode allows highly controlled particle manipulation.
TL;DR: In this paper, an alternative model using simplified voltage-current equations is developed to represent these spark properties rather than an arc characteristic, and the predictions of the partial arc model and this new approach are both tested here, using published experimental data from light-pollution fog tests in the authors' laboratory.
Abstract: The established model of the flashover of an insulator, whose surface is covered with a moist, conducting layer of pollution, envisages that it develops from the formation and bridging of a dry band by a partial-arc pre-discharge. This pre-discharge is assumed to possess arc characteristics, so that the electric field across the dry band will fall as the partial arc current increases. Observations of insulators which are only lightly polluted, however, show that pre-discharges are of low luminosity and rich in ultraviolet, and resemble the spark leader inception and extension sequence in air gaps. This is because the current limitation by low values of surface-layer conductance can inhibit the transition to an arc at the pre-discharge stage. An alternative model using simplified voltage-current equations is developed to represent these spark properties rather than an arc characteristic. The predictions of the partial-arc model and this new approach are both tested here, using published experimental data from light-pollution fog tests in the authors' laboratory. For this purpose, the partial-arc theory is further developed in order to reveal its implied prediction for the increase of pre-discharge length with applied voltage before flashover. A corresponding relationship is obtained for the increase of spark leader length using the new model. It is found that for light pollution, the dry-band spark model better represents the test data than the partial-arc model. Consequent predictions are made for the variation of flashover voltage with pollution severity in this regime, which may account for anomalous insulation failures.
TL;DR: In this paper, the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field, but the influence of PRTV coating will not remarkable to accumulate ice when there is heavy ice on insulators.
Abstract: How to decrease the ice on insulators and increase the flashover voltage of iced insulator are hot topics of power system in the world. Many tests have been carried out to investigate whether the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field. Firstly, the test to investigate the icing and electrical characteristic of dc insulator with PRTV coating was carried out. Moreover, comparison has been made between artificial polluted insulator and field polluted insulators. Results indicate that the PRTV coating can not decrease the ice accretion on insulators. Instead, it results in accumulating more ice at the beginning of icing regime, but the influence of PRTV coating will not be remarkable to accumulate ice when there is heavy ice on insulators. . In addition, the PRTV coating can decrease the flashover voltage by 10%. It is also revealed that the flashover voltage for the artificial polluted insulators is lower than that of the field polluted insulators due to the non-uniform of the natural pollution.
TL;DR: A three-dimensional nanoscale liquid glass electrode (NLGE) made from monolithic substrates without conductive materials by femtosecond laser nanomachining is reported, which can be easily integrated into other nanodevices and fluidic systems, including actuators and sensors.
Abstract: Nanofluidic devices make use of molecular-level forces and phenomena to increase their density, speed and accuracy1. However, fabrication is challenging, because dissimilar materials need to be integrated in three dimensions with nanoscale precision. Here, we report a three-dimensional nanoscale liquid glass electrode made from monolithic substrates without conductive materials by femtosecond-laser nanomachining. The electrode consists of a nanochannel terminating at a nanoscale glass tip that becomes a conductor in the presence of high electric fields through dielectric breakdown, and returns to being an insulator when this field is removed. This reversibility relies on control of nanoampere breakdown currents and extremely fast heat dissipation at nanoscale volumes. We use the nanoscale liquid glass electrode to fabricate a nano-injector that includes an electrokinetic pump, 4 µm across with 0.6 µm channels, which is capable of producing well-controlled flow rates below 1 fl s−1. The electrode can be integrated easily into other nanodevices and fluidic systems, including actuators and sensors. Glass undergoes a reversible dielectric breakdown under high electric fields at the nanoscale, allowing it to be used as an electrode for fluidic devices such as electrokinetic pumps.