Decrease Of Dielectric Strength Research Articles

Synchronous switching of uncompensated transmission line, by considering the effect of coupling voltage between the phases, trapped charge and the characteristics of CB

AbstractThe synchronous closing technology is an effective way to reduce transient current and voltage, prevent equipment failures, and improve power quality. The proposed algorithm, first by considering the coupling voltages between phases and the residual voltages in an uncompensated transmission line, calculates the zero instant of the voltage curves (ZVC instant) across the poles of the circuit breaker (CB) that is ideally the optimum instant to close the CB. Although other studies have utilized ZVC detection by solely considering either coupling or residual voltages. Secondly, the algorithm seeks to account for the mechanical scattering time of the CB and the rate of decrease of dielectric strength (RDDS) by incorporating delay times into the previously calculated delay values. Although other works have investigated the effect of RDDS or mechanical scattering operation time on synchronous switching to some extent, they have not fulfilled any optimization taking both of them into account.By exerting this algorithm, each phase of CB is closed in the ideal optimum closing target (ZVC instant) with a maximum error of one sample, and then, taking into account the CB characteristics, by compensating the RDDS and mechanical scattering time, CB is energized in the optimal time interval, where pre‐strike voltages are minimized.

Novel multifunctional melamine borate - boron nitride nanosheets/epoxy composites with enhanced thermal conductivity, flame retardancy and satisfying electrical insulation

In this work, we present a solution to use nitrogen and boron co-effect flame-retardant (melamine borate, abbreviated as MB) functionalized boron nitride nanosheets (MB-BNNS) to improve the thermal conductivity and flame retardance of epoxy resin and maintain excellent electrically insulating properties simultaneously. In brief, the MB-BNNS were prepared by grafting MB onto boron nitride surfaces via a simple ball-milling and eco-friendly water scrubbing process. Subsequently, the epoxy composites with uniformly dispersed MB-BNNS were obtained by wet processing. The obtained epoxy composite with 5 vol% EP/MB-BNNS showed a optimally comprehensive performance. Compared to pure epoxy, it showed 108% of increase in thermal conductivity (TC), 36.44% and 32.06% of decrease in peak heat release rate (PHRR) and total heat release rate (THR), and slightly decrease in dielectric breakdown strength. More remarkably, the release percentages of toxic and combustible gases in EP/MB-BNNS composite system were significantly reduced, which were measured by a in-situ measurement.

Analysis of Short-Circuit and Dielectric Recovery Characteristics of Molded Case Circuit Breaker according to External Environment

A molded case circuit breaker (MCCB) is one of the most important factors for safety to protect a load from overcurrent in a power distribution system. MCCB, which is mainly installed in switchboards and distribution boxes, may be affected by external temperatures and magnetic fields, but the above factors are still excluded from product standards and performance evaluation. This paper is the result of experimenting and studying the negative effects of these external temperatures and external magnetic fields on MCCB with short-circuit characteristic and dielectric recovery strength. As a result of temperature, it can be found that both short-circuit characteristic and dielectric recovery strength change linearly in accordance with the external temperature. The ratio of the values of 35 °C to 25 °C and 45 °C to 25 °C show the following results. t10, t21, and t32 are 1.58, 1.53, and 1.79, respectively, in short-circuit characteristics and ti, tm, and tl are 1.59, 1.69, and 1.53, respectively, in dielectric recovery strength. Depending on the external magnetic field, the short-circuit characteristics decreased by 8.56% only in the t21 period. The dielectric recovery strength decreases by 4.92% in the initial section (ti) and 14.45% in the later section (tl), respectively. It has been confirmed that the external magnetic field interferes with the emission of hot gas.

Investigation of Hydrothermal Aging on Polyvinyl Chloride (PVC) Used in Medium Voltage Cables

This investigation deals with the effect of hydrothermal aging on the electrical insulating properties of polyvinyl chloride used in medium voltage cables. The evolution of dielectric properties (dielectric loss factor, dielectric constant, dielectric strength and volume resistivity) as a function of aging time and temperature has been studied. After that, the mechanical characteristics (elongation at break and tensile strength) were also determined. Physico-chemical analysis was performed to highlight the structural changes induced by hydrothermal aging. Infrared spectroscopy using the Fourier transform (ATR-FTIR) and thermogravimetric analysis (TGA-DTA) have been performed. The results obtained show that the loss factor and dielectric constant increase gradually with the increase of temperature, while the volume resistivity decreases. At 100℃, the general shape of the curves giving the evolution of dielectric properties as a function of aging time shows that both loss factor and dielectric constant increase while those of volume resistivity and dielectric strength decrease. In the case of 80℃, the loss factor decreases slightly and the dielectric constant remains almost constant with aging time, whereas the volume resistivity and dielectric strength increase. The activation energy varies with aging time. The impact of hydrothermal aging on the properties of the material has been established in this study. At the beginning of aging, the degradation is mainly due to the elimination of molecular HCl. At more advanced stages of aging, the degradation is attributed to the elimination of HCl and double bonds formation followed by a change in color. Other consequences of the degradation like crosslinking and swelling of the samples are also noticed.

Improved electrical resistivity-temperature characteristics of insulating epoxy composites filled with polydopamine-coated ceramic particles with positive temperature coefficient

Incorporating positive temperature coefficient (PTC) ceramic particles into polymer matrices provides a promising solution to suppress the distortion of DC electric field within polymeric insulation caused by the negative temperature coefficient (NTC) of electrical resistivity. However, along with the suppressed NTC effect comes the decrease of dielectric strength due to the agglomeration of PTC particles. Here, we addressed this issue in the epoxy resin system by coating polydopamine onto PTC particles to improve the compatibility with matrix, thus achieving a maintained DC breakdown strength. The improved evenness of PTC particles dispersion also provided sufficient interface to generate interface charge traps, which contributed to the increase of electrical resistivity at elevated temperature. Combined with temperature dependent charge carrier amount affected by PTC filler, NTC effect of epoxy composites was further mitigated and the maximum DC electric field was reduced by 49% within insulation assessed by the simulation of HVDC bushing. The method proposed in this paper is crucially important for the reliable and economic application of composite dielectrics under harsh conditions.

Study on the Decrease in Air Dielectric Strength of DC Voltage According to the Ignition Properties of Combustibles

Most electrical transmission lines are located in forests, and currently in South Korea, deregulation has allowed various structures to be built on the ground below transmission lines. Events of fires occurring below high-voltage transmission lines can lead to large-scale electrical accidents. To prevent such accidents, this study examined the ignition properties of combustible materials and their relationship with the reduction in air dielectric strength. Experiments were performed on two types of synthetic resins and lumbers, namely cypress and pine. A cone calorimeter was used to measure ignition properties such as effective heat of combustion, heat release rate, and soot yield. In addition, we built a dielectric strength testing device to measure the reduction in air dielectric strength caused by flames. These measurement results can serve as a basis for revising fire safety standards.

ОПЫТНО-ПРОМЫШЛЕННЫЕ ИСПЫТАНИЯ СИСТЕМЫ RFID-КОНТРОЛЯ ИЗОЛЯТОРОВ

The paper considers results of pilot tests of a system for RFID-control of bracket insulators on signalling and interlocking lines and longitudinal power supply lines on an operating railway section. The system for RFID-control includes bracket insulators with built-in RFID-indicators, a registration device and software. The aim of tests is to assess a new method of contactless control of dielectric conditions of insulators in operation on an operating power transmission line. In condition of decrease of dielectric strength the system for RFID-control fixes the fault insulator by the registration device and with the use of software determines its exact location on a controlled section of an aerial power supply line. On the first stage all studies are carried out with the use of developed prototype of a portable RFID-registrator that determines operation areas of RFID-indicators in the area of a signalling and interlocking line pole. An operator fixes response signals of insulators after every 30° moving radially after every 1, 2, 3, 4 and 5 m regarding a power supply pole. As a result of studies of the first stage, the authors have developed a technology for installation of an indicator on bracket insulators of an operating power transmission line. Moreover, they have substantiated an introduction of the system for RFID-control of VL insulators in networks with insulated neutral for signals and interlocking lines and longitudinal power supply lines.

TECHNOLOGY AND EQUIPMENT FOR ACCELERATED REGENERATION OF OIL AND ADSORBENT, USED IN THE POWER INDUSTRY, USING A POWERFUL HF ELECTROMAGNETIC FIELD

The article presents the method of drying the adsorbent by an electro-magnetic field. Shown is the technology of the possession for the fast regeneration of naphtha and the adsorbent from the intake of the forced HF electromagnet field. During operation of the transformer, the oil absorbs atmospheric moisture and its dielectric strength decreases. To reduce the water content of the oil, it is pumped through a reservoir containing an adsorbent such as zeolite or silica gel. The adsorbent that has lost its sorption capacity can be restored by removing moisture by heating. The adsorbent can be processed by calcining it on metal sheets or heating it in sealed containers under reduced pressure using heating coils. The use of the first method leads to the destruction of the adsorbent during its transition from the adsorber and vice versa.

Effects of Filler Configuration and Moisture on Dissipation Factor and Critical Electric Field of Epoxy Composites for HV-ICs Encapsulation

Molding compounds (MCs) are widely used as an encapsulation material for integrated circuits; however, traditional MCs are susceptible to moisture and charge spreading over time. The increase in dissipation factor due to the increase of parasitic electrical conductivity ( $\sigma$ ) and the decrease in dielectric strength $(E_{\mathrm {MC}}^{\mathrm {Crit}})$ restrict their applications. Thus, a fundamental understanding of moisture transport as a function of MC parameters is essential to suppress moisture diffusion and broaden their applications. In this article, we: 1) propose a generalized effective medium and solubility (GEMS) Langmuir model by identifying a set of parameters that control water uptake as a function of filler configuration and relative humidity; 2) investigate the dominant impact of reacted-water on $\sigma $ through numerical simulations, mass-uptake, and dc conductivity measurements; 3) investigate electric field distribution to explain how moisture ingress reduces $E_{\mathrm {MC}}^{\mathrm {Crit}}$ ; and finally 4) optimize the filler configuration to lower the dissipation factor, and enhance $E_{\mathrm {MC}}^{\mathrm {Crit}}$ . The GEMS-Langmuir model can be used for any application (e.g., photovoltaics, biosensors) where moisture ingress leads to reliability challenges.

Statistical analysis of switching overvoltages in UHV transmission lines with a controlled switching

The objective of this work is to present a more precisely controlled switching strategy to reduce overvoltages due to ultra-high voltage (UHV) transmission line closing. Essentially the switching strategy is to find a suitable circuit breaker (CB) optimal instant of closing. The electric field variation in the arc-extinguish chamber has great effect on rate of decrease of dielectric strength (RDDS), when calculating optimal instant of closing with pre-breakdown between the contacts. The relative value k of a CB is defined as the ratio of RDDS to the rate of voltage approaching the zero cross. In this calculation, the electric field E should be as a variation due to the uneven medium of SF6. Consequently equations were derived from calculating the pre-breakdown instants. The ATP model of controlled closing UHV transmission line was built for switching overvoltage simulations considering RDDS and mechanical dispersion. The simulation results show that switching overvoltages are more accurate and closer to reality when regarding the electric field E as a variation. Contrarily, assuming E as a constant will increase the risk of failure via controlled switching. Furthermore, the simulation results demonstrate that k value can change the effect of the mechanical dispersion on switching overvoltages.

Investigation on optimal filler loadings for dielectric strength enhancement of epoxy/TiO2@SiO2 nanocomposite

Insulation plays a critical role in all electrical systems. Ever increasing voltages in power system demand conscientious research on insulation materials. To enhancing the electrical/mechanical properties of insulation materials, nano composite polymer insulations materials are of main interest for researchers since last two decades. This study presents the dielectric properties of an epoxy nano composite with filler consisting of TiO2 nano particles encapsulated in SiO2 core–shell. The particular combination used in this study is only reported once in an earlier research. In previous research filler, concentration range was from 0% to 4% by weight and it was reported that less than 1% loading gives best results. This key objective of this work was to find a precise filler loading value below 1%, which could give highest dielectric strength of resulting epoxy nano composite. The range investigated in this work was from 0.3% to 0.8% by weight. This range has never been investigated in literature previously. Electrical and chemical characterizations of prepared epoxy nano composites was carried out by using SEM, EDX, leakage current, resistivity, relative permittivity and dielectric strength analysis. The best results were achieved at 0.6% filler loading in base epoxy. A decrease in dielectric strength was observed in filler loading exceeding 0.6%, which is due to hydrophilic nature of TiO2@SiO2 which starts to dominate at higher loadings. In addition to this, uniform dispersion of nano-filler is a key requirement to get all the benefits of a formulated nano composite.

BST-P(VDF-CTFE) nanocomposite films with high dielectric constant, low dielectric loss, and high energy-storage density

Free-standing, flexible, and transparent ceramic-polymer nanocomposite films with a uniform thickness of about 5 μm were fabricated using a simple spin-coating process, in which the polymer solution with a high concentration was used. Ba0.5Sr0.5TiO3 (BST) nanoparticles and P(VDF-CTFE) 91/9 mol.% (VC91) copolymer were used as ceramic filler and polymer matrix, respectively. Microstructures, dielectric properties, and energy-storage performances of the BST-VC91 nanocomposite films have been investigated. With increasing volume fraction of BST, the dielectric constant increases, while the dielectric loss decreases. A dielectric constant of about 38.4 at 100 Hz associated with a dielectric loss of only about 0.02 was obtained in the nanocomposite film with 40 vol% of BST. It is experimentally found that the temperature dependences and the frequency dispersions of dielectric properties were strongly influenced by the volume fraction of BST, especially at high temperatures. Good temperature stability and small frequency dispersion of dielectric constant can be obtained in the BST-VC91 nanocomposite films with 40 vol% and 50 vol% of BST, which are also associated with a low dielectric loss. It is concluded that the motion of the polymer chains is the micro-origin of the relaxation process observed at high temperatures. With increasing volume fraction of BST, the dielectric breakdown strength decreases, while the maximal polarization and remnant polarization increase. The maximal charge-energy density and discharge-energy density of about 21.7 J/cm3 and 7.5 J/cm3 are obtained in the BST-VC91 nanocomposite film with 30 vol% BST under 2500 kV/cm, which are more than 2 times larger than those observed in pure VC91 film under the same electric field.

High voltage resistance ceramic coating fabricated on titanium alloy for insulation shielding application

To endow the insulation shielding of electromechanical devices, a TiO2 based ceramic coating with high voltage resistance was fabricated on titanium alloy by plasma electrolytic oxidation (PEO). The effects of PEO coatings with different phase composition and microstructure on insulation performance were determined. The results show that the ceramic coating formed in the silicate-based solution was mainly composed of rutile, anatase TiO2 and Al2TiO5. As the coating thickens from 10 to 36 µm, the increasing cross-sectional porosity enables the dielectric strength decrease from 32.94 ± 2.1 V/μm to 11.9 ± 0.71 V/μm and the electric resistivity drop from 1.17 × 108 Ω cm to 0.99 × 108 Ω cm respectively. With 2 g/L KOH added into the basic electrolyte, the thickness of coating significantly increased to 50.0 ± 2.1 µm, accompanied by the enhanced crystalline degree of rutile TiO2 phase and the decreasing of internal defects. In this way, the optimum coating with preferable resistivity of 1.08 × 1010 Ω cm, high breakdown voltage of 617.78 ± 26.31 V and dielectric strength of 12.36 ± 0.53 V/μm was achieved.

Effect of film structure and morphology on the dielectric breakdown characteristics of cast and biaxially oriented polypropylene films

Effects of cast film extrusion and biaxial orientation on morphological development and DC dielectric breakdown performance of non-oriented and biaxially oriented polypropylene (BOPP) films were studied. Cast films, based on two capacitor-grade isotactic polypropylene (iPP) homopolymers, were manufactured using three different extruders under different crystallization conditions and subsequently biaxially oriented using a laboratory stretching machine. Analysis of polymorphic composition and microstructural features was carried out in conjunction with large-area multi-breakdown performance assessment under progressive DC voltage ramp conditions. Polymorphic α/β-form crystalline composition and spherulitic/trans-crystalline morphology formed during cast film extrusion were found to directly affect the biaxially oriented film morphology and breakdown characteristics. For the BOPP films, decrease in dielectric strength was traced back to β→α crystal transformation and subsequent microvoid/porosity formation upon biaxial stretching. Topographical features and increasing surface roughness were also found to correlate with lower BOPP film dielectric strength. Dependence of breakdown strength on the biaxial stretch ratio was demonstrated, with higher biaxial stretch ratio resulting in improved BOPP film breakdown performance. As an extreme case, the biaxially oriented films were compared against non-oriented cast films in similar thickness range, highlighting the essential role of biaxial orientation in the high-dielectric-performance of thin films in capacitor applications. Control of polymer design as well as optimization of film processing and morphological development was found to be necessary to avoid formation of structural defects and loss of electrical insulation integrity.

Examination of dielectric strength of thin Parylene C films under various conditions

Abstract The breakdown voltage of the biocompatible polymer Parylene C was determined after storage in 60°C saline solution and treatment by autoclave. It occurred that both, storage at 60°C in saline solution and autoclaving, lead to distinct decrease of dielectric strength by approximately 50%.

Investigation of the dielectric relaxation, conductivity and energy storage properties for biaxially oriented poly(vinylidene fluoride-hexafluoropropylene)/poly(methyl methacrylate) composite films by dielectric relaxation spectroscopy

The dielectric relaxations in biaxially oriented P(VDF-HFP)/PMMA composite films with less than 40 % PMMA were investigated using dielectric relaxation spectroscopy. Various relaxation processes and their locations of P(VDF-HFP), PMMA, and P(VDF-HFP)/PMMA composite films were analyzed. According to the fitted data of the Havriliak–Negami (HN) function, different relaxation processes belong to non-debye relaxation, the activation energy (Ea) and dielectric relaxation strength (∆e) of P(VDF-HFP)/PMMA composite films significantly decreased around and above glass transition temperature (Tg) with increasing PMMA content. In addition, the conductivities (σ) of P(VDF-HFP)/PMMA composite films also sharply decreased with the addition of PMMA. The decrease of dielectric relaxation strength (∆e) benefits the drop of Pr, lower the activation energy (Ea) makes coercive field decrease and the lower conductivity (σ) could enhances the breakdown strength. Thus, dielectric film of high energy storage density and low loss was closely related with the lower Ea, ∆e and σ.

Investigations Into 25- and 30-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math> </inline-formula>-Thick Glass Capacitors at 23 °C and 235 °C and Area Dependence of Dielectric Strength of Alkali-Free Schott Inc. AF 32 ECO Glass

Parallel-plate capacitors constructed with 25- and 30- $\mu \text{m}$ -thick alkali-free glass sheets are demonstrated in pulsed $RC$ discharge circuit. Capacitance values ranged from $\sim 25$ to 54 nF. Capacitors were charged and discharged with an electrically triggered switch into resistive loads and were tested at 23 °C in oil up to 3.2 kV and up to 235 °C in air with a charge voltage of 350 V. Peak currents greater than 160 A were measured for multiple capacitor charge and discharge cycles for the capacitor submerged in oil. To our knowledge, this is the first demonstration of an ultrathin glass capacitor with multikilovolt charge voltage implement in a pulsed power electrical circuit. In addition, the dielectric strength of 25- $\mu \text{m}$ -thick alkali-free Schott Inc. AF 32 ECO glass is investigated in Shell Diala oil at room temperature as a function of electrode area spanning a factor of 600. The results show that as electrode area increases dielectric strength significantly decreases. Implications for the decrease in dielectric strength at large dielectric areas are discussed in regard to manufacturing ultrathin glass capacitors. Dielectric strengths measured for AF 32 ECO glass are in agreement with similar compositions of alkali-free glass.

Synthesis and electrical properties of hydrogen bonded liquid crystal polymer

In this study, a new polystyrene based side chain liquid crystalline polymer (EP-PS-LC11)) has been prepared from polystyrene having ethylpiperazine moiety as a hydrogen bond acceptor polymer and 11-(4-cyanobiphenyl-4(-oxy)undekan-1-ol (LC11) as a bond donor by molecular self-assembly processes via hydrogen bond formation between nitrogen of ethylpiperazine on polymer chain and hydroxyl group of the LC11. The formation of hydrogen bond has been confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the EP-PS-LC11 has been investigated by a differential scanning calorimeter (DSC) and polarized optical microscopy. The thermal behaviors of the H-bonded liquid crystalline polymer have been investigated by DSC measurements. The dielectric properties and ac conductivity mechanism of EP-PS-LC11 have also been investigated by impedance spectroscopy within the frequency interval of 5Hz–15MHz. The dielectric relaxation type of EP-PS-LC11 has been analyzed by fitting dispersion curves of ε′-ω. The system obeys nearly Debye and non-Debye type relaxations for the low and high frequency regions. In addition, it has been revealed that since the dielectric strength decreases by increasing frequency, the LC composite molecules can align more easily at high frequency. Moreover, the variation of imaginary component of dielectric constant with frequency shows two relaxation peaks. While the low frequency relaxation peak corresponds to molecular vibration, the high frequency relaxation peak is attributed to molecular orientation. The frequency dependence of ac conductivity has also been analyzed by means of frequency exponent, s. Depending on the frequency deal with, the system exhibit nearly dc, correlated barrier hopping (CBH) and super linear power law (SLPL) behaviors.

Glass transition and segmental dynamics in poly(l-lactic acid)/graphene oxide nanocomposites

Effects of graphene oxide (GO) and GO modified with dodecylamine (org-GO) on glass transition and segmental dynamics of poly(l-lactic acid) (PLLA) were investigated by differential scanning calorimetry (DSC) and two dielectric techniques, broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) techniques. Measurements were performed on initially amorphous and on crystallization annealed samples. Isothermal crystallization in the neat matrix and the nanocomposites was followed by DSC and BDS with the same thermal protocol. No change in the glass transition temperature is observed by DSC, whereas the heat capacity step decreases in the nanocomposites. The segmental α relaxation becomes faster and broader in the nanocomposites and its dielectric strength decreases. The results were rationalized in terms of a fraction of interfacial polymer becoming immobilized in the nanocomposites. Changes of this interfacial polymer fraction with composition and functionalization show similar trends in DSC and BDS, absolute values are, however, larger by BDS.

Fast switching response and dielectric behaviour of fullerene/ferroelectric liquid crystal nanocolloids

The electro-optical and dielectric responses of the fullerenes C60-doped ferroelectric liquid crystal (FLC) nanocolloids are reported. Order parameter and phase transition temperature remain invariant as a function of varying dopant concentration (0.10 wt% to 0.50 wt%). Faster switching response of nanocolloids comparing to that of the non-doped FLC is manifested by increase in the localised electric field (around 76% increment for 0.50 wt%), while reduction in the spontaneous polarisation could be the result of anti-parallel correlation amid dopant and FLC dipoles. Decrease in dielectric constant, absorption strength, dielectric strength and rotational viscosity of FLC nanocolloids than that of non-doped FLC is the other consequence of C60 doping. Goldstone-mode relaxation frequency is found to be increased with increasing doping concentration of C60 in FLC.