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Present study deals with the acquisition and analysis of different types of incipient discharges in transformer by adopting Ultra-High Frequency (UHF) technique. The Nyquist rate sampling method generates a large number of samples, making it inefficient for developing an online monitoring system. To reduce this, compressive sensing techniques are employed for signal compression and reconstruction. Various compressive sensing methods, including Convex, Non-Convex, Greedy, and Iterative Thresholding, were compared. Orthogonal Matching Pursuit (OMP) was found to be the optimal algorithm, achieving optimal reconstruction time and error at a compression ratio of 45%. The reconstructed signals were compared with the originals using Fast Fourier Transform (FFT), revealing similarities in dominant frequencies. A Long Short-Term Memory (LSTM) machine learning model was used for signal classification, consistently outperforming other algorithms. This study enhances understanding of incipient/partial discharge detection and classification, highlighting the effectiveness of innovative signal processing and machine learning approaches in power system engineering. [ABSTRACT FROM AUTHOR]

Background: Electro-permeablization using a pulse generator is a novel non-invasive approach for cancer therapy. It serves as a cell permeability enhancing agent for cancer treatment. Objective: In this article in vitro investigation of the effect of 1.0 kV/cm, 1.5 kV/cm and 2.0 kV/cm, 50 μs duration pulsed electric field on MCF-7 cell line has been done. Furthermore, combinational therapy of curcumin and electrical pulses has been also investigated. Material and Method: A variable voltage (100 V-1200 V, 100 V step) and 50 μs duration pulse generator has been designed, which is further used for the investigation of electroporation and destructive electrical field intensity. Investigation of the effect of electrical pulses on cancer cells has been performed using Trypan Blue Exclusion Test, MTT Assay and Clonogenic Assay. Results: It has been observed that electrical field intensity of 2 kV/cm, 50 μsec duration, 10 pulses at repetition rate of 1 pulse per second corresponding to total energy of 4 J is more than enough for causing necrotic cell death due to permanent damage of cell membrane of the cancer cell. Also, it has been observed that electrical pulse application enhances curcumin uptake by cells. Conclusion: Electrical pulses can effectively inhibit the cancer cell growth and proliferation. Furthermore, observation shows that electroporation enhances the curcumin uptake, therefore, it can be used for therapeutic purposes. [ABSTRACT FROM AUTHOR]

This research paper aims to examine the current state and future of sustainable aviation, electric aviation, and pollution-free aviation. The paper will explore the various technologies and innovations that have been developed to reduce the environmental impact of aviation, including fuel-efficient airplane designs, lightweight materials, and cleaner engines. It will also discuss the potential of electric aviation, which offers a promising alternative to traditional fossil-fueled airplanes. The paper will evaluate the benefits and challenges of these sustainable aviation solutions, and offer recommendations for how the aviation industry can continue to reduce its carbon footprint and minimize its impact on the will be of interest to anyone who is invested in creating a more sustainable and environmentally friendly aviation sector. [ABSTRACT FROM AUTHOR]

The effect of corona aging on the surface potential dynamics and charge trap characteristics of silicone rubber alumina nanocomposite are examined using surface potential decay measurement. The aging was carried out by exposing the specimens to corona stress generated by a high‐frequency AC multi needle‐plane electrode system. The results show that the addition of alumina filler increases the surface potential decay time and maximum trap energy. A reduction in trap depth is observed with the corona aging, and the addition of alumina filler limits the degradation and change in charge trap distribution. The results of an analysis of the space charge behavior of different nanocomposites and their comparison are presented. The space charge variation analysis was carried out under the applied electric field of 20 kV/mm at room temperature using the pulsed electro‐acoustic technique (PEA). Based on the results, the charge density, electric field, and charge trap distribution were deduced. It is concluded that the space charge concentration and enhancement in the electric field of the aged material increases with aging duration and it is maximum in the case of 60 min corona‐aged pure silicone rubber. Analysis of the recovery of the charge dynamics of the sample after corona discharges at the different time intervals shows that the recovery of trap distribution is faster for a virgin sample and slower for the sample with 5 wt% of alumina. [ABSTRACT FROM AUTHOR]

This article reports an experimental investigation of the impact of magnetic field on corona discharge activity in mineral oil, using both ultrahigh-frequency (UHF) and fluorescence techniques under ac voltage. The results show that corona inception voltage (CIV) increased under ac voltage with varying harmonic frequencies without considering any phase shift and reduced marginally under magnetic field. In addition, the impact of the magnetic field shifted the dominating frequency of the UHF signal (0.9 GHz) obtained under ac voltage toward lower frequencies (0.3 and 0.6 GHz). Under high magnetic fields, the parameters such as rise time, fall time, and pulsewidth of the fluorescence signal increased in its magnitude compared to its effect without a magnetic field. Also, using both the UHF sensor and the fluorescence sensor, there was no clear difference in the phase-resolved partial discharge (PRPD) pattern caused by corona discharge (with and without magnetic field). Furthermore, the number of discharges is observed to be high under the impact of harmonic ac voltages with third- and seventh-order containing total harmonic distortions (THDs) of 4% and 40%. [ABSTRACT FROM AUTHOR]

This work reports an experimental and theoretical analysis of the rheological properties of mineral oil-based SiO2 nanofluid for their potential applications in transformer insulation. The flow electrification mechanism on the nanofluids with different surfactants such as cetyl trimethyl ammonium bromide (CTAB), oleic acid, and Span 80 is studied using a spinning disk technique. The results show a higher streaming current for the nanofluids with CTAB as a surfactant compared to oleic acid and Span 80. The rheological behavior of nanofluids is explored with the double gap concentric cylinder geometry. The variation of shear stress with shear rate follows a power law relationship along with a yield stress observed for all the nanofluids. A transition is seen from storage modulus to dominant loss modulus for the nanofluids during the frequency sweep analysis, whereas no transition is observed in the case of mineral oil. In addition, regression analysis using artificial neural network (ANN) algorithms are performed on the experimentally measured viscosity of the nanofluids in order to estimate theoretical parameters and provide insights into the streaming current formation. The desirable rheological characteristics of nanofluids are identified for achieving enhanced insulation performance in transformers. [ABSTRACT FROM AUTHOR]

In the current research, we have synthesized Ni doped zinc oxide nanoparticles by solvothermal method at four different ratios (X = 2%, 4%, 6% and 8%). The samples were characterized for structural analysis by X-ray diffraction, morphological analysis by Field Emission Scanning Electron Microscope, elemental composition by Energy Dispersive Spectral Analysis, optical properties by UV Visible absorption studies, photoluminescence studies, Fourier Transform Infrared Analysis, Magnetic properties by Vibrating Sample Magnetometer of (x=2%). As a application of this work all the samples were subjected to test for the degradation of Rhodamine 6G dye under visible light and exhibited a better photocatalytic activity. [ABSTRACT FROM AUTHOR]

This article reports the static electrification of ester nanofluids for its use in transformers adopting the spinning disk model. The results show that the streaming current is higher for the nanofluid involving surfactant compared to its effect without surfactant. The streaming current observed is negative at the fluid–metal interface and positive at the fluid/pressboard interface. The streamline pattern along with surface velocity magnitude is simulated under different disk velocities using COMSOL and the convection current model is formulated for the identification of streaming current. The mass transfer rate with surfactant-based nanofluid shows a shift from transport regime to reaction limited regime at higher Reynolds number. Furthermore, the interfacial zone of nanofluids is discussed for the streaming behavior considering its influence with the addition of benzotriazole (BTA). [ABSTRACT FROM AUTHOR]

Silicone rubber incorporated with micro-aluminum trihydrate and varying weight fraction of nano-alumina fillers was fabricated and investigated for its space charge and trap-controlled mobility characteristics upon subjecting it to salt-fog aging. The space charge characteristics were studied by using pulsed electro-acoustics. The accumulation of space charge and its density was found to increase with the number salt fog aging cycles. The space charge decay rate and the trap-controlled mobility of silicone rubber specimens during depoling, have decreased, whereas trap depth has increased with the number of cycles of salt fog aging. After salt fog aging, the 2.5 wt.% nano-alumina added silicone rubber micro-nanocomposites have shown better performance with respect to space charge accumulation and space charge decay rate. The enhancement of electric field during the polarity reversal test has occurred with number of salt fog aging cycles. Its enhancement factor during polarity reversal was found to be lower with 2.5 wt.% nano-alumina added silicone rubber micro-nanocomposites, upon salt fog aging. The enhancement of electric field along with reduction in the trap-controlled mobility was observed with increasing number of salt fog aging cycles. [ABSTRACT FROM AUTHOR]

The micro-aluminium trihydrate (ATH) and nano-alumina fillers in the silicone rubber (SR) significantly improve the electrical, thermal and mechanical properties. ATH fillers improved the resistance to the corona ageing and water droplet-initiated erosion. Scanning electron microscopy (SEM) analysis was carried out to understand degradation condition caused due to corona ageing and damage caused due to water droplet-initiated discharges. The inclusion of these fillers significantly altered the surface and bulk charge distribution characteristics of the polymer. A right shift is observed in the trap distribution characteristics. The reduced electric field threshold limit for space charge formation is observed with composites, due to increment in impurities/agglomerations with respect to increment in filler concentration. Performance of composites subjected to polarity reversal is improved on inclusion of nano-filler in addition to micro-filler. The inclusion of fillers enhanced the thermal conductivity and improved significantly thermal stability of the SR composite. [ABSTRACT FROM AUTHOR]

Life expectancy of a thermally aged oil impregnated pressboard (OIP) in the presence of corrosive dibenzyl disulphide (DBDS) is studied in this work using a fast estimation method based on level of diffusion of Cu contaminant. Data from laser induced breakdown spectroscopy (LIBS) is used as the degradation parameter. Thermogravimetric analysis (TGA) is used for rapid evaluation of life expectancy at various temperatures. Aged OIP material is tested for its surface flashover breakdown strength and its thermal stability is studied by TGA and differential scanning calorimetry. Thermal activation energy is estimated using Flynn-Wall-Ozawa method and is agreement with isothermally calculated values. Aging law is derived and found to be nearly first order based on which temperature dependent life expectancy law is formulated. LIBS data of OIP collected from a failed transformer is considered to be end-of-life condition. Estimated life expectancy values using proposed fast method are compared with traditional long-aging evaluation and are in good agreement. Increase in corrosive DBDS concentration and change in aging medium using proposed method and are found to have a significant impact on life expectancy of the OIP insulation. [ABSTRACT FROM AUTHOR]

The effect of nanoclay on tensile properties is studied by dispersing the different weight percentages (0 wt%, 2 wt%, 4 wt% and 6 wt%) of montmorillonite (MMT) clay in the silicone rubber and hybrid rubber (EPDM/silicone rubber) samples. The thermal properties are also studied by using different instruments such as dynamic mechanical analyser (DMA), differential scanning calorimetry (DSC) and thermogravimetric analyser (TGA). The glass transition temperature (Tg) values obtained from DMA are correlated with DSC, both the values match well. The thermal stability and change in mass of above mentioned materials as a function of temperature are measured using thermogravimetric analysis (TGA). Fourier transformed infrared spectroscopy (FTIR) is used to characterise the grafting of clay in the silicone and hybrid rubbers. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of dielectric strength on transformer oil reliability and on a reproduction of a voltage breakdown simulation during a dielectric strength test. A typical Foster test cell was used in order to measure the dielectric strength of a variety of oils. For a more complete picture, it requires the identification of more parameters but this paper examines only the above one as a result of the operation of a testing apparatus. It is shown that FEM/FDM analysis provides same information for the electrode gap. Bruce electrode provides highly uniform electric field. Factors such as voltage rate, relaxation time between measurements as well as the shape of the testing electrodes influences the dielectric strength of the liquid. [ABSTRACT FROM AUTHOR]

Traditional outdoor insulators are made of glass and porcelain. However, although such insulators have been used for many decades, they present some drawbacks. Glass and porcelain insulators seem to be more prone to surface discharges and flashover when they age and water droplets are more likely to spread on their surface, causing thus dry zones and consequently conditions for surface discharging and flashover. Room Temperature Vulcanized (RTV) coatings spayed on the aforementioned traditional insulators seem to remedy such problems because such coatings increase the hydrophobicity. In this paper, a short review on RTV coatings is given together with some thoughts and comments regarding the so-called early stage of aging. [ABSTRACT FROM AUTHOR]

This paper reports the key findings from an experimental study carried out on thermally aged natural ester fluid impregnated pressboard (EOIP) material. The results show that the surface discharge inception voltage (SDIV) with thermally aged EOIP material is higher under negative DC voltage compared with positive DC and AC voltage. The SDIV increases with AC voltage frequency and a minimal reduction in voltage was observed under harmonic AC voltages with different total harmonic distortion (THD). The rate of change in voltage due to ripple content in DC voltage affects the SDIV of EOIP material, initiating discharges at lower voltages. The UHF signals radiated during the surface discharge process have a bandwidth in the range 0.9 to 2 GHz. Surface potential variation studies indicated the formation of high trap sites and trap density due to thermal aging. A reduction in the oxidation onset temperature and the activation energy of thermal decomposition were observed with thermally aged EOIP material. A pyrolysis study showed high composition of levoglucosan and acidic residue with the thermally aged specimen, which reduces its degree of polymerization. Impedance spectroscopic analysis indicates a non-Debye type of relaxation with thermally aged EOIP material. The mobility and charge transfer characteristics were also inferred from the modulus spectroscopy which showed less change for thermally aged pressboard material. [ABSTRACT FROM AUTHOR]

This work studies the impact of silica nanoparticles on the dielectric properties of synthetic ester oil. A stable nanofluid is prepared by addition of surfactant. With addition of nanoparticles there is an increment in dielectric constant and decrement in dielectric loss constant. An attempt is made to understand the conduction mechanisms in uniform field and non-uniform electric field configuration by means of analysing the mobility of ions. Under uniform electric field stress (<0.1 kV/mm), by means of conduction current measurement with polarity reversal, the ionic mobility, conductivity, ionic concentration and ionic radius are deduced. There is a reduction in ionic mobility by addition of nanoparticle and surfactant. To understand the conduction mechanisms in high electric field condition, the current-voltage characteristics of the nanofluid are measured. Using this data, apparent mobility due to electrohydrodynamic motion is estimated, giving a lower mobility in the case of nanofluid, which could be the cause of the increased corona inception voltage. [ABSTRACT FROM AUTHOR]

This study shows that TiO 2 nanofiller and cetyl trimethyl ammonium bromide (CTAB) surfactant in ester oil demonstrates higher corona inception voltage under AC and DC voltages. Flow electrification studies with nano fluid adopting the spinning disk method confirms that the streaming current increases with increasing pressboard thickness, disc diameter, oil temperature and spinning disk velocity. The study also indicates that nanofluids with surfactant have higher streaming currents than its effect without surfactant. It is found that the streaming currents could be suppressed by the addition of aromatic additive 1, 2, 3-benzotriazole (BTA). In addition, the permittivity of the nanofluid is not affected by adding surfactant or BTA but a marginal reduction occurs with increasing temperature. However, the loss tangent of the nanofluid with surfactant and BTA shows an increase with increasing temperature. The rheological studies indicate transition from laminar to turbulent flow in the case of nanofluids. [ABSTRACT FROM AUTHOR]

This paper refers to some factors affecting the breakdown strength of solid insulating materials. Solid insulating materials play a most important role in the high voltage industry. Factors, such as area effect, crystallinity, impregnation with liquids, temperature, the role of interfaces and mechanical stressing, are investigated and commented upon. [ABSTRACT FROM AUTHOR]

In this study, the degradation of tensile properties is investigated by placing the neat ethylene propylene diene monomer (EPDM) rubber and different weight percentages (2 wt%, 4 wt% and 6 wt%) of MMT clay dispersed in the EPDM rubber samples in a humidity chamber for 0, 5, 7, 12 and 14 days. The thermal properties of neat EPDM rubber and its clay nanocomposites were studied by using different instruments, namely dynamic mechanical analyser (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The viscoelastic properties are studied over the temperature range of −80°C to 80°C at different frequencies by using DMA. An increase in storage modulus and the decrease in loss tangent values are observed with the increase in clay content from 0 wt% to 6 wt% in EPDM rubber. Increase in storage modulus and glass transition temperature (Tg) values is observed with the increase in frequency from 1 Hz to 50 Hz. Also, the thermal stability and change in mass of these materials as a function of temperature and time are studied using TGA. It is found that EPDM/4 wt% clay composites exhibit the highest residual weight at 690°C while neat EPDM exhibits the highest weight loss compared to samples dispersed with other clay weight percentages. Using X-ray diffraction (XRD), 2θ value was measured and the crystal structure is investigated. Fourier transformed infrared spectroscopy (FTIR) was used to characterise the grafting of clay in the EPDM rubber. The dielectric constant and conductivity were studied for different frequencies and temperatures. [ABSTRACT FROM AUTHOR]

Addition of alumina nano particles to silicone rubber (SR) has shown a significant improvement in electrical, mechanical and thermal properties of the SR nanocomposites. Static contact angle and water droplet-initiated corona inception voltage exhibited a marginal change on inclusion of nano alumina into SR matrix. Alumina filler improved the corona ageing resistance of the composites; however, a marginal reduction in the rate of hydrophobicity recovery is observed. Laser induced breakdown spectroscopy proved as an effective tool to rank the performance of the SR nano composites. Variation of crater depth with energy of laser pulse and number of laser pulses follows the exponential relation. Plasma temperature calculated by optical emission spectroscopy is in line with the amount of damage caused to the surface of the specimen by water droplet-initiated discharge. Dielectric response spectroscopic studies indicate that inclusion of nano fillers has resulted in lower interfacial polarization and lower imaginary permittivity. It is observed through dynamic mechanical analysis that the composites have higher storage modulus and the activation energy compared to base SR. [ABSTRACT FROM AUTHOR]

Ester oils are evolving as next-generation transformer insulants, and it is essential to understand their characteristic variation upon thermal ageing. Corona inception voltage reduces with thermally aged ester oil under AC and DC voltages. The UHF signal generated due to corona discharge activity has energy content in the range 0.4–4 GHz. The magnitude and energy content of the UHF signal formed due to corona activity increases with thermally aged oil. Ionic mobility studies are carried out to understand the impact of thermal ageing on polarization and depolarization current, ion concentration, and ionic radius formed in the oil. Thermal ageing of ester oil leads to an increase in the ionic mobility of oil samples along with an increment in the ionic concentration. The conductivity of oil is observed to increase with ageing, accompanied by a reduction in ionic radii. The effect of voltage stress shows enhanced conductivity for thermally aged oil samples. Dielectric response spectroscopy exhibits higher loss and permittivity values for thermally aged oils. The physicochemical analysis shows a gain in viscosity, moisture content and turbidity, and a marginal loss in thermal conductivity due to the formation of new molecular species. UV analysis exhibits a significant redshift in the oil sample aged at a higher temperature. [ABSTRACT FROM AUTHOR]

The study of epoxy nano micro composites clearly indicates that the material has better dielectric properties with a good discharge resistance and less surface charge accumulation on its surface. The impact of high-frequency AC voltage and the percentage of ripple content in DC voltage on corona inception caused by water droplets was analyzed. Under a high frequency, the variation in the shape of the water droplet is the same as that under 50 Hz AC voltage. The UHF signal radiated due to water droplet initiated discharges have signal bandwidth in the range of 300 MHz-3 GHz. The influence of corona discharge on surface properties of the material, its variation to contact angle and water droplet initiated corona activity under AC voltage was analyzed. The surface potential characteristics were altered with corona-aged specimen. The impact of an ion-trapping particle on nanocomposites clearly exhibits its characteristics through surface potential studies. Water diffusion into the insulating materials varies with the type of filler material. The temperatures measured during arcing, analyzed through laser-induced breakdown spectroscopy (LIBS), were correlated with the hardness of the material. In addition, the mechanical properties, especially storage modulus and tan δ, were analyzed through dynamic mechanical analysis (DMA) studies. [ABSTRACT FROM AUTHOR]

A new class of insulating materials is the class of polymer nanocomposites. In the past twenty-five years, a lot of attention was paid to the various electrical, thermal and mechanical properties of polymer nanocomposite materials. In the present work, epoxy resin samples without and with nanoparticles (0 wt%, 1 wt%, 3 wt%, 5 wt%, and 10 wt%) are investigated regarding the surface discharges and the flashover voltages. Four different water droplet arrangements were used, with eight different water conductivities in order to see the effect of the nanoparticle content on the surface discharges and the flashover voltages. [ABSTRACT FROM AUTHOR]

Pulsed wire discharge is used to produce Sn-0.75 Cu nanoparticles (NPs) from Sn-0.75 Cu solder wire in argon ambient. The energy stored in the capacitor (W), which is in the multiple of the sublimation energy of the wire, is discharged through the wire at different pressure of argon. All the particles are spherical in shape with minimum mean particle size of about 28 nm. Deposited energy to the wire increases with increase in W and time to melt of the wire after the injection of current reduces with increase in capacitor voltage. XRD shows peaks corresponding to Sn with no presence of Cu for all the cases. EDAX confirms the presence of Cu. Reduction in melting point of NPs with decreasing size is observed with theoretical and DSC study. Reduction in particle size is observed with increasing energy ratio, K (ratio of W to sublimation energy of the wire) and/or decreasing pressure, P of Argon gas; confirmed with experimental measurement of particle size done with transmission electron microscope (TEM) micrographs and, theoretical calculation of activation energy and nucleation rate of NPs formation. [ABSTRACT FROM AUTHOR]

Incipient discharges formed due to corona activity, surface discharge, and particle movement in transformer insulation are identified based on acoustic emission signals captured using fiber Bragg grating sensors and analyzed in the frequency domain. To improve the SNR of these signals, the use of an adaptive line enhancement-based technique is systematically explored through simulations, and the associated parameters are optimized. The noise-filtered spectra analyzed through ternary diagrams suggest the possibility of classifying the discharges which are further validated using appropriate classifiers. The experimental comparison of discharges generated in different oil media like mineral oil, nanoparticle-dispersed mineral oil, ester oil, and nanoparticle-dispersed ester oil reveals that the discharge characteristics are similar across multiple media, and the classification holds good. [ABSTRACT FROM AUTHOR]

Synthetic ester oil (SEO) is becoming a replacement for mineral oil in transformers due to its biodegradability and for its better insulation properties. Silica nanoparticles dispersed in SEO can increase its corona inception voltage (CIV) and breakdown voltage compared to pure SEO. Physico-chemical studies were carried out to understand the characteristics of nanoparticles and nanofluids. Methodical experimental studies were carried out to understand the corona discharge activity in SEO based nanofluid. A ultra-high frequency (UHF) sensor was used to identify corona activity and it is concluded that the UHF signal radiated from corona activity in SEO and nanoparticle dispersed SEO have a bandwidth in the range of 700 MHz to 2 GHz. A comparative study on the CIV of SEO and nanofluid under harmonic AC voltages has been carried out, which indicates a reduction in the CIV as the total harmonic distortion of the supply voltage increases. Phase resolved partial discharge analysis indicates that the magnitude of discharges formed in nanofluid is much lower than in the SEO. Comparative statistical analysis are made with the breakdown voltages of the synthetic ester oil and nanofluid. A comparative analysis on the energy of the UHF signal due to the corona discharges is performed. [ABSTRACT FROM AUTHOR]

Incipient discharges formed in natural ester oil due to corona activity, surface discharges and particle movement were investigated using UHF technique. When the applied voltage magnitude is increased, on the inception of discharges, the peak to peak magnitude of the voltage of the UHF signal formed also increases. After certain applied voltage magnitude increase, if it is reduced, the magnitude of UHF signal formed is much higher than the magnitude of the signal formed when the voltage is increased. This phenomenon is observed with all the three types of discharges. Cross Recurrence plot (CRP) can be effectively used to determine the Time Difference Of Arrival (TDOA) of UHF signals. Self-similarity Recurrence Quantification Analysis (RQA) parameter is found to be more suitable technique to estimate the TDOA of UHF signals. CRP method is used to estimate TDOA correctly, even with low signal to noise ratio and it is found to be superior to Cross-correlation technique in estimating the TDOA. Estimated TDOA of UHF signals are validated and incipient discharge source is localized by adopting the non-iterative technique. [ABSTRACT FROM AUTHOR]

Titania (TiO 2) nanoparticles with cetyl trimethyl ammonium bromide (CTAB) surfactant dispersed in transformer oil has higher corona inception voltage than the normal transformer oil, under AC, DC, and composite AC and DC voltages. It is observed that corona inception voltage is lower under composite voltages compared to AC and DC voltages. The corona activity radiates ultra high frequency (UHF) signals with its dominant frequency near 1 GHz. Operating a spectrum analyzer in zero span mode, the UHF signals generated from the corona activity, the number of discharges is observed to be more under composite voltages than under AC voltages, both at inception and at higher voltages. A reduction in interfacial tension and an improvement in flash point is observed in nano-titania with surfactant dispersed transformer oil. The addition of surfactant reduces the turbidity of the nanofluid. Phase Resolved Partial Discharge (PRPD) analysis with UHF signals measured, indicates that corona discharge activity occurs around the peak and the pre-peak rising portions of the supply voltage. It is observed that more discharges occur in the positive half cycle for AC superimposed with positive DC voltage and in the negative half cycle for AC superimposed with negative DC voltage. The magnitude of UHF signals formed due to corona activity is less with nanofluid, irrespective of voltage profiles. [ABSTRACT FROM AUTHOR]

This study focuses on characterization of silicon carbide (SiC)‐epoxy nanocomposites with different mass loading of SiC using different techniques to evaluate the physicochemical, thermo‐physical and surface discharge activity of the insulating materials. A marginal increase in surface discharge inception voltage (SDIV) was observed with increase in wt% loading of SiC in the epoxy but not much variation is observed with increase in supply frequency. Surface discharge process radiates electromagnetic waves in the UHF signal frequency range of 0.5–1.5 GHz. The dielectric properties of the material get altered with the percentage of SiC material in epoxy resin. TEM analysis indicates uniformity of dispersion of nano particle in epoxy resin. Charge retention capability of the material is high when the deposited charges are unipolar. Optical emission studies indicate the presence of silicon peaks with SiC‐epoxy nanocomposites in wavelength range of 350‐400 nm. Oxygen peaks were observed for all samples. Using the spectral peak positions and intensities of the peaks obtained, the plasma temperature for SiC‐epoxy nanocomposites was estimated to be c.a. 2240 K low when compared to that for pure epoxy. LIBS spectra clearly indicate an increase in carbon intensity with corona damaged specimen. Also for the same level of fluency, the amount of damage is less with higher percentage of SiC included epoxy nanocomposites. Pyrolysis GC/MS study indicates that the presence of SiC in the epoxy matrix enhances the timescale of primary pyrolysis vapors such as bisphenol components to form more monomeric phenols via secondary cracking reactions. POLYM. COMPOS., 39:3268–3279, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The levitation voltage of the conducting/non conducting particle in the SF6 gas filled electrode gap is high under DC voltage compared with the AC voltage. The levitation voltage increases with frequency of the supply voltage. Particle levitation voltage marginally increases with increase in THD of the harmonic AC voltage. The levitation voltage of the particle increases as and when the barrier is moved towards the high voltage electrode. No polarity dependency is observed on levitation voltage under DC voltages. Percentage of filler content in epoxy nanocomposites has high impact on levitation voltage of the particle. The analysis of levitation voltage with epoxy nanocomposites indicates that up to 3 wt% of MgO added specimen, the levitation voltage is high and above which a marginal reduction in levitation voltage of particle in SF6 gas medium is observed. The UHF signal magnitude caused by the particle movement process increases with the applied voltage. Also, the extinction voltage of particle movement is lower than the levitation voltage. Also, with increase of applied voltage, on levitation, the magnitude of UHF signal increases. However, on reducing the applied voltage, the UHF signal magnitude is much higher than onward application of voltage. This characteristics is almost the same under AC and DC voltages. The FFT analysis of UHF signal formed due to particle under AC and DC voltages, at the point of inception has dominant frequency at around 1 GHz. When the applied voltage is increased, especially under DC voltages, the FFT analysis of UHF signal formed indicates energy content in the band 2-3 GHz is increased, indicating indirectly, the rate of charge transfer due to particle movement with opposite electrode is high under DC voltages. The FFT analysis of UHF signal formed by non-conducting particle under high frequencies have the energy content increased in the range 2-5 GHz. PRPD analysis indicates that PD activity is observed in the entire phase of the applied AC voltage, irrespective of harmonics and THDs. The number of PD occurrence is high where the rate of rise of supply voltage is high. [ABSTRACT FROM AUTHOR]

The molecular level changes in natural ester oil due to thermal aging are studied. Accelerated thermal aging of natural ester oil at 180°C is performed and the subsequent effect on oil matrix is studied using corona inception voltage (CIV) variation under AC and DC voltage. Various physico-chemical diagnostic techniques such as UV-Vis absorbance, FT-IR, fluorescence microscope, DLS, and TEM were used to study the thermally aged natural ester oil. Thermal aging leads to the reduction in corona inception voltage as observed in the present work. The CIV is much higher under DC voltage than AC voltage but its variation is not much under positive/Negative DC voltage. Spectrum analyzer measurement indicates that burst type discharges occur under negative DC voltages. Thermal aging induces degradation of natural ester oil, resulting in the formation of carbonaceous particles. As these carbonaceous particles are fluorescent in nature, a facile fluorescence based analysis is developed to understand and monitor its degradation. 3D excitation emission matrix (EEM) fluorescence data are modeled with parallel factor analysis (PARAFAC). [ABSTRACT FROM AUTHOR]

Cellulosic pressboard is a key insulation material in oil filled transformers. Surface discharge or partial discharge degrades the insulation material and reduces the life time of the transformer. This study is aimed at understanding the effect of thermal aging of pressboard on the variation of its surface discharge and chemical characteristics. Thermal degradation of pressboard was carried out at 180 °C for 500 h in presence of ester oil under simulated aging conditions. The variation of salient electrical characteristics like surface discharge inception voltage (SDIV), charge measurement and optical emission spectra of the discharges were assessed at different aging periods. A significant reduction in SDIV was observed due to thermal aging. The charge measurement indicated that total charge deposition on pressboard increased with aging duration. Optical emission spectroscopy yielded valuable information regarding the elements evolved during discharge activity. Chemical characterization of the virgin and aged pressboard samples was carried out using analytical pyrolysis coupled with gas chromatograph-mass spectrometric technique (Py-GC/MS). The production of anhydrosugars, furan derivatives and oxygenates from the pressboard increased with aging time, while the esters in the oil were degraded to carboxylic acids with aging. Owing to the weakening of the hydrogen bonding network in oil impregnated pressboard with thermal ageing, high yield of end-chain depropagation products like anhydrosugars was observed during pyrolysis. The weak sites in cellulosic pressboard are expected to act as charge deposition sites. [ABSTRACT FROM AUTHOR]

Impact of thermal ageing of pressboard material in transformer oil containing dibenzyl disulphide (DBDS) under different ambience, such as air, N2, He and vacuum has been studied to understand the level of copper sulphide diffusion. The characteristic variations in electrical and thermal properties of copper sulphide diffused oil impregnated pressboard (OIP) material have been measured under different ageing conditions. Surface charge accumulation studies with AC and ?DC voltages showed that surface charge decay time was longer in air aged OIP material. Surface discharge studies by adopting ultra-high frequency (UHF) sensing indicated a reduction in the SDIV with the level of ageing although the characteristic variation in flashover voltage (FOV) under lightning impulse (LI) voltage is almost the same. Also the SDIV reduced with increase in frequency of supply voltage. Thermo-gravimetric analysis (TGA) indicated that maximum weight loss temperature (Tmax) of the cellulose constituent of OIP material decreased with ageing. Laser induced breakdown spectroscopy (LIBS) was adopted to quantify the diffused copper sulphide contaminant in OIP material and the results were compared with the inductively coupled plasma (ICP) spectroscopy based analysis. Based on these studies, deteriorating effect of ageing medium on several properties of OIP material was understood. [ABSTRACT FROM PUBLISHER]

Corona activity on the surface of silicone rubber has high impact on variation in hydrophobicity of the material, and on corona inception voltage (CIV) of water droplet sitting on the corona degraded surface. The CIV is high under negative DC as compared to positive DC/AC voltages. Increase in conductivity of water droplet reduces CIV. Surface charge accumulation studies indicate that the charge retention capability of the insulating material gets reduced drastically with silicone rubber damaged due to corona causing degradation of surface. Irrespective of the number of cycles of corona discharge activities carried out, the time constant of charge decay, after the removal of charge injection, remains the same. The water droplet initiated discharges under AC and DC voltages radiate UHF signal in the bandwidth 0.3?1.2 GHz. With single droplet sitting on top of the corona damaged silicone rubber, the amount of charge retained by the water droplet is low when the droplet is placed and charged immediately after corona discharge activity to surface of the insulating material. When the water droplet is placed after a certain time period, the charge accumulation characteristics of silicone rubber are regained. Leakage current measured during water droplet discharge studies through recurrent plot (RP) analysis reveals that, under AC voltage, it is possible to classify corona inception, arcing and bridging of water droplet between high voltage and ground electrode. The RP obtained for the current signals generated due to water droplet discharges under positive and negative DC voltages are different. The amount of damage caused to silicone rubber due to water droplet is high under negative DC voltage as compared to positive/AC voltages. While correlating the level of damage to the insulating material due to water droplet and the RQA parameters of RP, it is observed that higher the recurrence rate along with high determinism can cause severe damage to the insulating material. Structural analysis using ATR-FTIR and pyrolysis-GC/MS studies reveal significant functional group variation on surface of silicone rubber, especially when the number of cycles of corona ageing is more. [ABSTRACT FROM AUTHOR]

Titania (TiO2) nanoparticles dispersed transformer oil has high Corona Inception Voltage (CIV) and breakdown strength, and gets further enhanced on insertion of the barrier in the electrode gap. The volume of nanoparticles and the amount of surfactant have a strong influence on the dispersion of nanoparticles in transformer oil and were characterized through viscosity measurement, particle size analysis and by zeta potential measurements. It was also observed that with needle plane configuration, negative DC voltages have high breakdown voltage as compared to positive DC and AC voltages. Improvement in breakdown voltage with barrier can be obtained by placing the barrier at 20?80% of electrode gap from the tip of the high-voltage electrode. The breakdown voltage of needle plane electrode configuration was calculated based on normal distribution parameters. It was observed that the corona activity generates Ultra High Frequency (UHF) signal in the frequency range of 0.7?2 GHZ with its dominant frequency at 0.9 GHz and was characterized using a ternary plot. The discharge activity was studied by using a spectrum analyzer by operating it in zero span mode with 0.9 GHz as center frequency. It was observed that for a given voltage under AC and DC voltages, the magnitude of discharges is less with nanoparticles dispersed transformer oil. A pyrolysis study indicated no variation in the composition of the oil with the addition of titania. It was observed that the esters present in the oils were alkyl substituted oxalic acid and alkyl substituted sulfurous acid esters. [ABSTRACT FROM AUTHOR]

This paper deals with the flashover voltages on samples of silicone rubber/ethylene propylene diene monomer (SiR/EPDM) mixtures under the influence of a uniform electric field. Five different mixtures of SiR/EPDM were investigated. Various SiR/EPDM mixtures (100% EPDM, 10% SiR + 90% EPDM, 30% SiR + 70% EPDM, 50% SiR + 50% EPDM, 70% SiR + 30% EPDM, 90% SiR + 10% EPDM, 100% SiR) were tested for different water droplet arrangements, different water conductivities, different droplet volumes as well as different droplet positioning w.r.t. the electrodes. The 50% SiR + 50% EPDM mixture proved to be the best mixture regarding the flashover voltage. [ABSTRACT FROM AUTHOR]

In this paper, we propose the use of a Cross Recurrence (CR) Plot Analysis based technique applied on signals captured using fiber Bragg grating sensors to improve the accuracy of detection and localization of partial discharges. With the help of detailed simulations, the performance of the proposed technique in estimating the Time Difference of Arrival (TDOA) is evaluated. A novel technique of extracting the frequency from CR plots is also proposed and frequencies of single as well as multiple-tones signals are extracted successfully. Controlled experiments are conducted to verify the technique and the estimates of location are found to be within an error of less than a centimeter. [ABSTRACT FROM PUBLISHER]

Aluminum (Al) nanoparticles are synthesized by wire explosion process (WEP) in an inert ambience of argon. Thermodynamic analysis and structural characterization of nano Al particles are made in the present work. Transmission electron microscopy (TEM) characterization has shown that the Al nanoparticles produced are spherical in shape and it follows a lognormal distribution. A unimodal size dependent thermodynamic model is formulated to understand the size dependent thermal behavior of aluminum nanoparticles. Three different melting modes such as, homogeneous melting mode (HMM), liquid skin melting (LSM) and liquid nucleation and growth (LNG) are assumed to understand the melting behavior of aluminum nanoparticles synthesized by the WEP process. The effect of saturation ratio on the nucleation rate and the impingement factor is also discussed. The size dependent melting and enthalpy of fusion of Al nanoparticles predicted by thermodynamic model are in tandem with the DSC results. [ABSTRACT FROM AUTHOR]

Surface Discharge Inception Voltage (SDIV) of unaged and copper sulphide diffused Oil Impregnated Pressboard (OIP) material was studied by adopting Ultra High Frequency (UHF) technique. Copper sulphide diffusion into OIP material was carried out by thermal aging of pressboard material in Dibenzyl Disulphide (DBDS) added transformer oil. The SDIV reduces with increase of thermal aging temperature. The current pulse injected in positive and negative half cycle during the surface discharge of the AC shows the rise time of 0.8ns and 1ns respectively. The FFT analysis of UHF signal measured during surface discharge process has shown frequency content in the range 0.7?1.2 GHz with its dominant frequency at 0.9 GHz. The life of the charge presented on the pressboard increases with thermal aged specimen. Energy dispersive spectroscopy (EDS) analysis of OIP material indicates presence of copper and sulphur content. Frequency Domain Dielectric Spectroscopy (FDDS) studies indicate the permittivity(?r), dissipation factor (tan(?)), conductivity (?dc) increases and relaxation time (?), coefficient (?) decrease with OIP material (in air / Nitrogen) aged at higher temperature in DBDS added transformer oil. Cole-Cole double relaxation model was used to understand the dielectric parameters of copper sulphide diffused OIP material. The DC conductivity of pressboard material aged in DBDS included transformer oil follows Arrhenius law and the activation energy decreases with increase in temperature of thermal aging. [ABSTRACT FROM AUTHOR]

Tree-like-trees are observed with electron beam irradiated XLPE cable insulation under AC voltages. Charge accumulation studies indicate that the level of charge deposited by +/− DC corona charging is almost same. However, the amount of accumulated charge increases with increase in level of irradiation of electron beam. The decay time constants are marginally high with positive charge deposition. Moreover, the decay time constant of accumulated charges increases with increase in level of irradiation of the material. The rise time of injected current signal formed during tree growth in positive and negative half cycle is about 900 and 700 ps, respectively. The UHF signal generated during tree growth in virgin and with irradiated specimen has its frequency content in the range 0.5–1.5 GHz. Weibull distribution studies indicate that the life time of electron beam irradiated specimen drastically gets reduced due to treeing. Sequential measurement of UHF signal indicates that tree growth involves high and low intensity discharges. Phase resolved partial discharge studies using spectrum analyzer indicates that discharges occur at the raising portion or near zero crossing of the applied AC voltage. FTIR spectroscopy and analytical pyrolysis-GC/MS analyses of the electron beam irradiated samples reveal the formation of alkoxy and alkyl peroxy radicals, and carbonyl and hydroxyl groups via scission of the crosslinks. The weak crosslinking sites are proposed to act as nodal points from where tree growth occurs. [ABSTRACT FROM PUBLISHER]

Epoxy nanocomposites with different percentages of nano clay filler are prepared using a shear mixer technique. Corona inception voltage (CIV) due to water droplets on the epoxy nanocomposite is high under negative direct voltage compared with positive polarity voltage. It was found that an increase in droplet volume and number of droplets within the gap reduces the CIV. The magnitude of discharge current flow is high under negative polarity. Surface charge accumulation studies indicate nonlinear variation in distribution of charges on the surface of the epoxy nanocomposite with water droplets. Optical Emission Spectroscopy (OES) results confirm high temperature plasma during water droplet initiated electrical discharges on the surface of epoxy resin. Laser Induced Breakdown Spectroscopy (LIBS) results indicate the presence of carbon on the degraded surface of the sample. The absorbed energy on the sample surface during arcing is measured through leakage current, and is observed to be higher for negative polarity. UHF signals were radiated due to corona discharges from water droplets on the epoxy nanocomposites under direct voltages and their bandwidth is in the range of 1–2 GHz. [ABSTRACT FROM PUBLISHER]

In liquid nitrogen insulation, the corona inception voltage is high with barrier in the electrode gap. The breakdown voltage of needle-plane gap has increased with barrier positioned near high voltage needle electrode. The current signal injected due to corona discharge in liquid nitrogen insulation, at the point of its inception and during streamer formation, have rise time, in negative and positive cycle of the AC voltage are about 2.9 ns and 2.5ns respectively and the characteristics has not altered due to barrier insulation. The UHF signal generated by corona discharges, in the liquid nitrogen electrode gap (with/without barrier) have frequency contents between 0.5-1.5 GHz. The magnitude of UHF signal formed due to corona activity (with barrier) on inception and at higher voltages (not at point of near breakdown) shows inverse relationship. Corona discharge followed with breakdown studies analyzed using zero span analysis. Phase resolved partial discharge signatures obtained due to corona discharges indicates that phase window at which corona discharge occurs become narrow with barrier in the electrode gap. [ABSTRACT FROM PUBLISHER]