Show all 14 papers
P. Vinod, B.M.A. Desai, R. Sarathi, S. Kornhuber · IEEE Transactions on Dielectrics and Electrical Insulation · 2019
coronaLIBSnano aluminasilicone rubber
Characterizes how nanofiller loading changes the electrical, thermal, and mechanical performance of silicone rubber used in outdoor high-voltage insulation.
Key Finding: Nano-alumina filler improved corona ageing resistance in silicone rubber, though it modestly reduced hydrophobicity-recovery rate.
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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 to be 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.
B.M.A. Desai, R. Sarathi · IEEE Transactions on Dielectrics and Electrical Insulation · 2018
corona dischargecross-recurrence plotlocalizationTDOA
Develops a UHF-based signal processing technique to detect and pinpoint early-stage partial discharges inside transformer insulation before they cause failure - a diagnostic approach later adapted to biomedical signal processing.
Key Finding: Cross Recurrence Plot analysis localized incipient discharge sources accurately even under low signal-to-noise ratio, outperforming cross-correlation.
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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 a certain applied voltage magnitude increase, if it is reduced, the magnitude of the UHF signal formed is much higher than the magnitude of the signal formed when the voltage is increased. This phenomenon is observed with all 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 a 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 the Cross-correlation technique in estimating the TDOA. Estimated TDOA of UHF signals are validated and the incipient discharge source is localized by adopting a non-iterative technique.
B.M.A. Desai, P. Mishra, N.J. Vasa, R. Sarathi, T. Imai · Micro and Nano Letters · 2018
Corona ageingEpoxy nanocompositesLaser-induced breakdown spectroscopyWollastonite
Compares how different fillers in epoxy nanocomposites resist corona-discharge ageing, using laser-induced breakdown spectroscopy to characterize surface degradation.
Key Finding: Wollastonite-filled epoxy composite resisted laser abrasion where nano-micro silica-filled composites did not, indicating superior corona-discharge resistance.
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The research examines how corona aging affects epoxy nanocomposite surfaces, particularly measuring contact angle changes. Composites containing Wollastonite filler demonstrated superior resistance to corona degradation compared to those with nano-micro silica fillers. The study employed laser-induced breakdown spectroscopy (LIBS) to characterize material aging conditions by analyzing plasma temperature and threshold fluence. Epoxy composite with Wollastonite as filler was not affected by laser abrasion and demonstrated enhanced discharge-resistant properties.
B.M. Ashwin Desai, R. Sarathi, S. Kornhuber · INAE Letters · 2019
Laser Induced Breakdown SpectroscopyOptical Emission SpectroscopySilicone RubberWater Droplet Discharges
Uses two complementary spectroscopic techniques, optical emission and laser induced breakdown spectroscopy, to characterize water-droplet-triggered discharge activity on silicone rubber insulation surfaces.
Key Finding: Combined OES and LIBS analysis characterized discharge activity and surface degradation from water-droplet corona, informing long-term outdoor insulation performance under wet conditions.
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Water droplet initiated discharges on silicone rubber insulation surfaces were investigated using optical emission spectroscopy (OES) and laser induced breakdown spectroscopy (LIBS). These complementary spectroscopic techniques were used to characterize the discharge activity and surface degradation caused by water droplet corona on silicone rubber, contributing to understanding of long-term outdoor insulation performance under wet conditions.
P. Mishra, B.M.A. Desai, N.J. Vasa, R. Sarathi, T. Imai · Micro and Nano Letters · 2019
gamma irradiationepoxy nanocompositesdielectric relaxation spectroscopy
Studies how gamma-ray exposure alters the structure and performance of epoxy nanocomposites, relevant to insulation used in radiation-exposed environments.
Key Finding: Gamma-ray irradiation sharply reduced surface potential decay time and increased charge mobility in epoxy nanocomposites.
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Epoxy nanocomposites being used in the high-energy radiation zones as an insulant may undergo changes in their dielectric properties during service. In the present study, the performance of base epoxy resin (S1) is compared with epoxy resin with ion trapping particle (Sample S2) and epoxy resin with nanotitania (Sample S3) particle. The influence of gamma irradiation on nanocomposites was analysed. Corona inception voltage due to water droplet initiated discharge and contact angle reduces post-gamma-ray irradiation. Surface potential decay time constant reduced drastically for gamma-ray-irradiated specimens. Trap distribution characterisation indicated that charge mobility increases after irradiation. The surface roughness of the sample increases with the irradiation dosage. Dielectric relaxation spectroscopy shows that permittivity reduces and loss tangent increases with the gamma-irradiated specimens. Water diffusion rate increases for the gamma-ray-irradiated specimen. No change in elemental composition, measured using laser-induced breakdown spectroscopy, of test specimens was observed. The hardness of the material and plasma temperature formed during laser shine decreases with gamma-ray irradiation intensity for Sample S1, whereas samples S2 and S3 showed only marginal variation. The performance of Sample S2 is found to be better than Samples S1 and S3.
P. Vinod, B.M.A. Desai, R. Sarathi, S. Kornhuber · Electrical Engineering · 2021
AluminaCoronaSilicone rubberSpace charge
Examines how mixed nano- and micro-scale fillers affect charge trapping and thermal behavior in silicone rubber composites used for insulation.
Key Finding: ATH and nano-alumina fillers shifted the charge-trap distribution and improved thermal stability of silicone rubber composites.
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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 the thermal stability of the SR composite.
B.M.A. Desai, R. Sarathi, J. Xavier, A. Senugupta · ICIIS 2018 · 2018
Classificationpartial dischargesSVMTime Frequency transformation
Applies time-frequency signal transformation to automatically classify different sources of partial discharge - an early example of the signal-processing techniques now common in biomedical diagnostics.
Key Finding: A quadratic SVM classifier successfully distinguished partial-discharge sources from time-frequency transformed UHF signals under simulated field conditions.
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UHF signals generated by partial discharges due to corona activity, surface discharge and particle movement in transformer oil were acquired and used to develop a classification model. Time-Frequency transformation of the UHF signal emitted by the partial discharge source was used for classification of the discharges using a quadratic support vector machine (SVM) learning tool. The method was validated by simulating the field condition, by studying the classification model in an oil filled closed tank along with the pressboard along the path of the UHF signal, as observed in a real system.
A.D.B. Manjunath, F. Khan, N. Noyanbayev, N. Harid, H. Griffiths, R.P. Nogueira, N.T.C. De Oliveira, M. Haddad, S. Ramanujam · IEEE Transactions on Electromagnetic Compatibility · 2022
GroundingPermittivityResistivitySoil
Measures how the electrical resistivity and permittivity of soils and aqueous solutions vary with frequency and current density, informing more accurate grounding-system design.
Key Finding: Measured soil/electrolyte impedance across 1 Hz–10 MHz and 1–35 mA/m² current density, showing that electrode-electrolyte interface effects have caused prior studies to overestimate resistivity and permittivity.
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Soil parameter characterization and the variation of permittivity and resistivity with frequency (dispersion) and current density have been the subject of many experimental studies but significant differences in measured values are found in the literature due to different testing approaches, apparatus, and test sample composition. This article first presents a comprehensive review of this previous body of work. Then, new experiments on soils and electrolytes with test frequencies in the range 1 Hz to 10 MHz and with current densities from 1 to 35 mA/m2 are described. Such results help clarify the effects of frequency, soil moisture, electrolyte concentration, and electrode material on the measured test medium parameters. The contribution of the electrode-electrolyte interface (EEI) and the influence of current density are particularly highlighted. These findings indicate that some previous measurements may have overestimated the measured values of resistivity and permittivity due to the EEI effect. Finally, the test results are compared with soil parameter equations from CIGRE TB781.
G.D.P. Mahidhar, B.A. Kumar, R. Sarathi, N. Taylor, H. Edin, B.M.A. Desai · EIC 2021 · 2021
Generative Adversarial NetworksPartial DischargeTransformer insulationUHF technique
Uses generative adversarial networks (GANs) to reconstruct digital twins of partial-discharge signals, an early application of generative deep learning to insulation diagnostics.
Key Finding: A DCGAN reconstructed high-fidelity UHF partial-discharge signals, recovering realistic time-frequency characteristics from known defect models.
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Partial discharge (PD) monitoring is one of the diagnostic techniques adopted for identifying the variety of defects in transformer insulation. Ultra high frequency (UHF) technique is gaining importance in PD monitoring applications of transformers due to various advantages. Different types of incipient discharges arise from defects in transformer insulation that need to be identified. In an actual test site there can be noise that can hinder data acquisition, and defect identification can become difficult. By using artificially reconstructed signals of known practically occurring defect models, the loss in data can be overcome. In the present study, Deep Convolutional Generative Adversarial Networks (DCGAN) technique is adopted to reconstruct the UHF partial discharge signals with high fidelity. Time-Frequency characteristics of the signals were used to build the DCGAN network and the reconstructed UHF signals are evaluated by studying the frequency characteristics of the generated signal.
S. Mallayan, R.R. Prabhu, B.M.A. Desai, R. Velmurugan, R. Sarathi, B.N. Rao · Micro and Nano Letters · 2019
LDPE-clay nanocompositescorona inception voltagethermomechanical properties
Characterizes LDPE-clay nanocomposite films to understand how clay nanofillers alter electrical, thermal, and mechanical properties for insulation applications.
Key Finding: Nano-montmorillonite clay inclusion increased LDPE's corona ageing resistance and storage modulus while reducing loss tangent.
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The performance of low-density polyethylene (LDPE) clay nanocomposites was analysed. The inclusion of nano montmorillonite (MMT) clay in LDPE material has significantly increased the contact angle, corona ageing resistance, water droplet initiated corona inception voltage and surface discharge inception voltage of the composites. The surface charge decay rate of the samples significantly reduced on the inclusion of clay indicating modified trap distribution characteristics due to the inclusion of the filler. Dynamical mechanical analysis indicates increased storage modulus and reduced loss tangent due to nanofillers inclusion. Laser-induced breakdown spectroscopy indicates that on inclusion of nanofillers the plasma temperature increases and crater depth decreases. In particular, increased discharge resistance, improved thermomechanical properties are observed with LDPE-MMT clay composites compared to pure LDPE.
A.D.B. Manjunath, N. Harid, H. Griffiths, R.P. Nogueira, N. Noyanbayev, A. Haddad, S. Ramanujam · IEEE Transactions on Electromagnetic Compatibility · 2023
Circuit modelelectrode-electrolyte interface (EEI)impedancesoil conduction
Proposes equivalent circuit models to represent the impedance behavior of soils and aqueous solutions measured in a two-terminal configuration, simplifying grounding system analysis.
Key Finding: A constant-phase-element circuit model accurately reproduced electrode-electrolyte interface behavior across 10 mHz–10 MHz for both soils and electrolytes.
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Numerous circuit models have been proposed to represent the electrode-electrolyte interface (EEI) impedance and bulk medium impedance of conducting media. Following a review, two suitable models are constructed to represent the behavior of conduction in electrolytes and soils, respectively. Both models incorporate a constant phase element in parallel with an apparent Faradaic resistance, which is found to reproduce the EEI behavior accurately. For the electrolyte model, a single parallel R-C branch is added to represent the impedance of the bulk medium, whereas for the soil model, an equivalent ladder network of R-C branches is found to be suitable. Experimentally obtained electrolyte and soil impedance data based on 2-terminal impedance spectroscopy over a frequency range of 10 mHz to 10 MHz with variable current density are compared with values obtained from the models and where model parameters are determined by a curve fitting routine. The effects of electrolyte concentration, soil moisture, and electrode material are analyzed, and the models help to illustrate clearly how the EEI effect dominates at low frequencies while the intrinsic characteristics of the test medium prevails at high frequencies. The models are extended to account for soil-electrolyte impedance dependence on current density, which is most evident at low frequencies.
P. Mishra, B.M.A. Desai, R. Sarathi, T. Imai · IET Science, Measurement & Technology · 2019
Corona inception voltageepoxy nanocompositesTDOA
Investigates how water droplets on epoxy nanocomposite surfaces trigger electrical discharges under AC and DC stress, and localizes the discharge sites for diagnostic purposes.
Key Finding: Corona inception voltage from water-droplet discharges was highest under negative DC and lowest under AC excitation.
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Corona inception voltage (CIV) due to water droplet sitting over the surface of epoxy nanocomposite material depends on supply voltage frequency, the conductivity of water droplet and the contact angle of the test specimens. The contact angle of the specimen and CIV due to water droplet has a direct correlation. It is realised that the CIV is high under negative DC and the least under AC voltages. Surface charge accumulation studies indicate that the accumulated charge and its decay time constant reduces in the damage-caused zone due to corona activity. The ultra-high frequency (UHF) signal generated due to water droplet-initiated corona activity has frequency content in the range of 0.8-1 GHz. The localisation of incipient discharges is demonstrated by using the non-iterative technique and the cross recurrence plot (CRP) technique is used to estimate the time difference of arrival (TDOA) of UHF signals generated due to water droplet-initiated discharge. Laser-induced breakdown spectroscopy (LIBS) depicts the elemental composition and reveals the difference in plasma temperature and threshold fluence between all the test specimens.
M. Shadid, N. Harid, B. Barkat, A. Manjunath · UPEC 2022 · 2022
fault diagnosisFrequency response analysisimpulse methodTransformer
Uses transformer winding impulse-response signatures to detect internal turn-to-turn short circuits before they escalate into failures.
Key Finding: Impulse-response testing matched the diagnostic sensitivity of the standard swept-frequency method for turn-to-turn short circuits, in less test time.
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Several techniques are currently used to monitor internal defects in power transformers. These are very useful for reducing failure rates and extending the service life of transformers. One of the most sensitive techniques is the frequency response analysis method that injects a swept frequency ac signal into the transformer winding and analyses differences between the measured output signal and a benchmark reference signal. This paper applies the impulse voltage method for the diagnosis of turn-to-turn short circuit faults inside a transformer winding. The input signals are a set of impulse voltages of different shapes instead of the standard ac signals of variable frequency. The merits of this method compared with the standard swept frequency method are a shorter time for testing and for signal analysis. The output results are processed to produce a frequency response plot of the winding. Measurement results on a small test transformer show that the plots are closely similar to those obtained using the swept frequency method. In this initial study, impulse voltages are used to emulate the naturally occurring transients in power systems such as switching events and tap changer operations. The sensitivity of the method is verified by applying statistical techniques to interpret the measured frequency response in different frequency bands.
N.K. Haneefa, B.M. Ashwin Desai, R. Sarathi, M. Rathinam · SPCOM 2020 · 2020
dendrogramPartial dischargesunsupervised clusteringwavelets
Uses dendrogram-based clustering to separate overlapping partial-discharge signals when multiple discharge sources are simultaneously active - improving diagnostic accuracy in noisy conditions.
Key Finding: An unsupervised dendrogram-clustering approach successfully separated simultaneously active partial-discharge sources using cosine similarity of wavelet-based features.
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Partial discharges in transformer insulation are of major concern to utilities which cause the catastrophic failure of insulation. One of the major challenges is the identification of discharges from multiple sources when it occurs concurrently. Hence it is imperative to devise methods for identifying and separating those signals for corrective measures. In this study, an unsupervised learning approach is proposed for clustering of individual partial discharge signals and then using that information for separating the multi-source signals. Our clustering approach works by constructing a dendrogram by measuring the cosine similarity between the feature vectors and then computing a threshold, to group the individual source signals into different clusters. The feature vectors include the relative energies from the wavelet packet decomposed tree and the Higuchi fractal dimension of the wavelet coefficients at the terminal nodes. The generated clusters are trained using a classifier model to separate the individual and multi-source signals. The proposed approach is a simple and robust technique for individual cluster groupings and individual to multiclass separations and could be used for multiclass cluster groupings.
N. Noyanbayev, A.D.B. Manjunath, N. Harid · UPEC 2024 · 2024
impedance spectroscopyimpulse methodpermittivityresistivity
Applies an impulse-based impedance spectroscopy method to characterize the frequency-dependent electrical behavior of soils and aqueous solutions.
Key Finding: The impulse method matched frequency-domain impedance spectroscopy accuracy while cutting measurement time and equipment cost.
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This study investigates the variation of soil resistivity and permittivity using the impulse method impedance spectroscopy. Experiments were conducted with an aqueous solution of Na2SO4 at varying concentrations and sand with different moisture contents. Measurements were taken in the frequency range of 1 Hz to 10 MHz using multiple double exponential waves. The results derived from FFT analysis of time-domain data were compared with frequency-domain impedance spectroscopy (FDIS), highlighting the accuracy and efficiency of the impulse method in determining soil electrical parameters. The study demonstrates that the impulse method can provide reliable results with significantly reduced measurement time and equipment costs compared to traditional FDIS methods. Additionally, the impulse method's applicability in field conditions makes it a practical alternative for various soil impedance measurements, offering insights into soil behavior under different environmental conditions.