Pulse induced failures in bi-axially oriented polypropylene capacitors: Experimental investigation

An experimental study of the absorption of high energy pulses in bi-axially oriented polypropylene (BOPP) capacitors is reported in the paper. The pulse handling performance test is used to identify the material or mechanical problem characteristics developed in the capacitor. The experiments are focused on samples of different film metallization and crystallinity and the results are compared in terms of current pulse handling capability as well as the level of impulse breakdown voltage. To assess the impulse handling capability, the proposed deterioration parameter is the number of absorbed pulses and Weibull cumulative probability of failure is presented. Experimental findings reveal specific types of failure development through the gradually elevated energy pulse test. The observed failures are either accidental, or progressive and they are located at the electrode terminal, or in the capacitor volume. The accidental failures are accompanied by no significant change in the additionally measured capacitance and loss factor, however, the characteristic fault location is in the capacitor volume. The progressive failure is caused by the gradual degradation of the insulating material where both the capacitance and the loss factor give a preliminary information of the impending damage, dominantly occurring at the electrode terminals. Possible reasons accounting for the certain failure type are discussed

Dielectric Fluids for Power Transformers with Special Emphasis on Biodegradable Nanofluids

This review is focused on the research of dielectric fluids, especially commonly used power transformer oils enhanced by nanoparticles, i.e., nanofluids. There are differences between various combinations of base fluids and nanoparticles prepared in different ways. The main goal of this review was to present recent research in this field sorted by the used nanoparticles. Nanofluids based on mineral oils, natural, or synthetic esters were investigated in terms of the nature of nanoparticles, particularly Al2O3, TiO2, Fe2O3, Fe3O4, graphene, fullerene, and others. The combinations of environmentally friendly oils and nanoparticles were presented. Finally, the article focused on the description of current dielectric fluids usable in power transformers and the possibilities of improving new and existing fluids with nanoparticles, especially their physical, dielectric, and chemical properties, but with regard to environmental aspects

The effect of SiO

The paper presents the impact of SiO2 nano-filler in epoxy resin (ER) on changes of dielectric properties and time to the breakdown. Several composites were tested with the mass fraction of 0.5 wt%, 1 wt% and 2 wt% of SiO2, respectively. The frequency spectra of the real and imaginary parts of complex dielectric constant were measured by a capacitance method within the frequency range from 1 mHz to 1 MHz. The mass fraction 0.5 wt% nanoparticles (NPs) in ER caused the evident decrease of the complex permittivity, while 1 wt% or 2 wt% yielded similar permittivity as measured in the pure ER sample. This change of the permittivity with the nano-filler concentration is discussed on the basis of the multi-core model. Moreover, SiO2 NPs also caused the frequency shift of the local maximum of permittivity to lower frequencies which corresponds with the α-polarization process. The internal partial discharges in the ER and its mixtures with the SiO2 nano-filler by the galvanic method and acoustic method are presented. The decrease of the time to breakdown with the increase of SiO2 the mass fraction is reported, too

Acoustic detection of noise emission from discharge activity in power engineering

This article deals with results from analysis of acoustic signal obtained from experiments realized in nonhomogeneous electric field. These signals exist in the form unwanted noise which can be used also for diagnostic purpose. In power engineering this case occure in high voltage power station and transmission lines. We analyse acoustic signal from acoustic sensor in audible band from 1 kHz to 20 kHz. The acoustic signal transmitted from object is unique for specific conditions. Exploitation of audible band for discharge detection is difficult in outdoor bias level. Advantage of this method consist in simple results prepare

Dielectric Performance of Natural- and Synthetic-Ester-Based Nanofluids with Fullerene Nanoparticles

According to the latest research, nanofluids as a possible future substitution for high-voltage equipment insulation have the potential to enhance the heat transfer and insulation properties of their base fluids. Dielectric properties are represented by breakdown strength (AC, DC, lightning) and dielectric performance as a set of quantities including dissipation factor, permittivity, and volume resistivity. In this study, natural and synthetic esters were mixed with C60 nanoparticles. Samples were examined for dissipation factor, relative permittivity, and volume resistivity at temperatures between 25 °C and 140 °C to monitor changes in dielectric performance with rising temperature, in accordance with IEC 60247. In addition, the samples were tested for AC breakdown voltage (using mushroom-like electrodes with a gap distance of 1 mm) and evaluated using the Weibull distribution statistical method. These measurements allowed complex evaluation of the examined mixtures and the determination of optimal concentration for each ester-based nanofluid

Assembly of 1D Granular Structures from Sulfonated Polystyrene Microparticles

Being able to systematically modify the electric properties of nano- and microparticles opens up new possibilities for the bottom-up fabrication of advanced materials such as the fabrication of one-dimensional (1D) colloidal and granular materials. Fabricating 1D structures from individual particles offers plenty of applications ranging from electronic sensors and photovoltaics to artificial flagella for hydrodynamic propulsion. In this work, we demonstrate the assembly of 1D structures composed of individual microparticles with modified electric properties, pulled out of a liquid environment into air. Polystyrene particles were modified by sulfonation for different reaction times and characterized by dielectric spectroscopy and dipolar force measurements. We found that by increasing the sulfonation time, the values of both electrical conductivity and dielectric constant of the particles increase, and that the relaxation frequency of particle electric polarization changes, causing the measured dielectric loss of the particles to shift towards higher frequencies. We attributed these results to water adsorbed at the surface of the particles. With sulfonated polystyrene particles exhibiting a range of electric properties, we showed how the electric properties of individual particles influence the formation of 1D structures. By tuning applied voltage and frequency, we were able to control the formation and dynamics of 1D structures, including chain bending and oscillation

Electric Field-Driven Assembly of Sulfonated Polystyrene Microspheres

A designed assembly of particles at liquid interfaces offers many advantages for development of materials, and can be performed by various means. Electric fields provide a flexible method for structuring particles on drops, utilizing electrohydrodynamic circulation flows, and dielectrophoretic and electrophoretic interactions. In addition to the properties of the applied electric field, the manipulation of particles often depends on the intrinsic properties of the particles to be assembled. Here, we present an easy approach for producing polystyrene microparticles with different electrical properties. These particles are used for investigations into electric field-guided particle assembly in the bulk and on surfaces of oil droplets. By sulfonating polystyrene particles, we produce a set of particles with a range of dielectric constants and electrical conductivities, related to the sulfonation reaction time. The paper presents diverse particle behavior driven by electric fields, including particle assembly at different droplet locations, particle chaining, and the formation of ribbon-like structures with anisotropic properties

Frequency-Dependent Dielectric Spectroscopy of Insulating Nanofluids Based on GTL Oil during Accelerated Thermal Aging

Improving the dielectric properties of liquid-insulating materials is a current problem in research into the insulation system of a power transformer. Modern optimization of insulating liquids involves the potential use of unique synthetic esters enriched with nanoparticles. This study presents the results of the dielectric response of liquefied gas-based (GTL) insulating liquids during accelerated thermal aging. The dielectric relaxation spectroscopy method was used in the frequency domain to point out power losses as an imaginary part of a complex electric modulus. The relaxation spectra express the validity of applying this complex dielectric parameter. The polarization processes of the base oil alternately change position in the low-frequency band during thermal aging. Fullerene nanofluid undergoes three phases of dielectric loss changes during thermal aging. In the case of magnetic nanofluid, the effect of electric double-layer polarization disappeared after 500 h of thermal aging. It was found that with the gradual increase in the thermal aging time, there is no gradual increase in the dielectric losses investigated in the measured frequency spectrum. This study shows that the concentration of the two types of nanoparticles independently causes a different dielectric response to an applied AC electric field in the GTL base fluid

Mechanochemical Synthesis of Nickel Mono- and Diselenide: Characterization and Electrical and Optical Properties

Nickel mono- (NiSe) and diselenide (NiSe2) were produced from stoichiometric mixtures of powdered Ni and Se precursors by the one-step, undemanding mechanochemical reactions. The process was carried out by high-energy milling for 30 and 120 min in a planetary ball mill. The kinetics of the reactions were documented, and the products were studied in terms of their crystal structure, morphology, electrical, and optical properties. X-ray powder diffraction confirmed that NiSe has hexagonal and NiSe2 cubic crystal structure with an average crystallite size of 10.5 nm for NiSe and 13.3 nm for NiSe2. Their physical properties were characterized by the specific surface area measurements and particle size distribution analysis. Transmission electron microscopy showed that the prepared materials contain nanoparticles of irregular shape, which are agglomerated into clusters of about 1–2 μm in diameter. The first original values of electrical conductivity, resistivity, and sheet resistance of nickel selenides synthesized by milling were measured. The obtained bandgap energy values determined using UV–Vis spectroscopy confirmed their potential use in photovoltaics. Photoluminescence spectroscopy revealed weak luminescence activity of the materials. Such synthesis of nickel selenides can easily be carried out on a large scale by milling in an industrial mill, as was verified earlier for copper selenide synthesis

Locomotor Activity of Ixodes ricinus Females in 900 MHz Electromagnetic Field

Mobile telecommunications technologies have become an indispensable part of people’s lives of all ages around the world. They affect personal life and social interactions and are a work tool in the work routine. Network availability requirements and the quality of the Internet connection are constantly increasing, to which telecommunications providers are responding. Humans and wildlife live in the permanent presence of electromagnetic radiation with just a minor knowledge of the impact this radiation has. The aim of our study was to investigate the effect of a 900 MHz electromagnetic field (EMF) on the locomotor behavior of female Ixodes ricinus ticks under laboratory conditions. Experiments were performed in the radiation-shielded tube (RST) test and radiation-shielded circular open-field arena placed in an anechoic chamber. Altogether, 480 female I. ricinus ticks were tested. In the RST arena, no differences in preference for irradiated and shielded parts of experimental modules were observed; in the open-field arena, the time spent and the trajectory passed was significantly longer in the part exposed to the EMF