Search

This work deals with the effect of oil reclamation on the conduction mechanism and dielectric aspects of accelerated thermally aged transformer mineral oil. The reclamation is a treatment with Fuller's earth (FE) adsorbent to remove corrosive sulfur compounds and other contaminants formed during thermal aging. The properties of the oil are compared between different stages of the treatment. Corona (partial discharge) inception is identified by the optical fluorescent fiber technique. The results show an increased corona inception voltage after treatment. Dielectric response spectroscopy (DRS) showed a lower loss factor and electrical conductivity after treatment. The conduction mechanism is measured under uniform and nonuniform electric fields with variations in applied voltage magnitude. The conduction mechanism at a uniform electric field (low E) is studied using the polarity reversal technique to estimate the respective ionic motilities in the fluid. The apparent mobility of ions, conductivity, ionic radius, and concentration from the oil are found to reduce on reclamation. In addition, the conduction mechanism for a higher electric field is simulated by the current-voltage characteristic in nonuniform conditions and the slope determines the ionic mobility of the fluid., QC 20231121

Present work deals with accelerated electrical and thermal stress on transformer oil and its characteristic variation on Fuller's earth (FE) reclamation. The influence of carbon particles in the fluid, its role on thermal ageing characteristics can be understood by electrical characterization. Reclamation of insulation fluid extends the lifetime and reliability of the transformer over the year of operation. The average particle size of carbon particles on electrical breakdown are in the range of 644 nm. Dielectric response spectroscopy (DRS) which identifies the conductivity and relative permittivity variation with the effect multi-stress ageing. Conduction mechanism with higher electric field is simulated by current-voltage (IV) characteristics using non-uniform field configuration to derive the ionic mobility of the liquid. Dissolved decayed products and turbidity showed drastic enhancement with multi-stress ageing than the thermally aged specimen. Reclamation with fuller earth treatment removes the carbon traces and ageing by-products in the fluid regaining its relative dielectric performances. Rheological aspects with viscosity indicates the ageing by-products build and also its characteristic variation on the reclamation process., Part of ISBN 9798350302172QC 20230919

This study reports experimental investigations of the effects of different surfactants (CTAB, Oleic acid and Span 80) on silica based synthetic ester nanofluids. The positive and negative potential observed for the ionic (CTAB) and non-ionic surfactant (Span 80) from zeta potential analysis indicates an improved stability. The optimization of nanofillers and surfactants is performed considering the corona inception voltage measured using ultra high frequency (UHF) technique and fluorescent fiber. Rheological analysis shows no significant variation of properties with shear rate, implying Newtonian behavior even with the addition of surfactant. In addition, the permittivity of the nanofluid is not much affected by adding surfactant but a marginal variation is noticed in the loss tangent with the effect of temperature. The fluorescence spectroscopy shows no change in the emission wavelength with the addition of silica nanofiller and surfactants. Flow electrification studies indicate an increase in the streaming current with the rotation speed and temperature, with a higher current magnitude observed in the case of nanofluids., QC 20220315

In recent times, nanoparticles-dispersed ester fluids are reported to exhibit improved thermal and electrical properties for its application in insulation system. In the present study, insulating nanoparticles of silica were dispersed in synthetic ester fluid to improve electrical characteristics of the base fluid. A two-step process involving mechanical shear mixing and ultrasonication was adopted for producing nanofluids. Physical and chemical characterization of nanofluids were carried out to estimate stability of the nanofluid with optimum concentration of nanoparticles and surfactants. To substantiate the influence of nanoparticles and surfactant on the dielectric properties of the nanofluid, conductivity measurements were made at low and high electric field conditions. It was observed that in the presence of electric field, the motion of ions is inhibited due to its trapping by the surface of nanoparticle, leading to lower ionic mobility. To explore the governing mechanisms further, electrical insulating performance of the nanofluid and corona discharge activity were investigated under AC and DC voltages using ultrahigh frequency (UHF) technique. This study has also shown an increase of 30% improvement in the corona inception voltage (CIV) upon addition of nanoparticles. The discharge activity was also mitigated due to incorporation of nanofillers in the fluid. The energy of discharge was found to be lower in nanofluid as compared to base fluid. It was evident from the present studies that silica-based nanofluids have shown superior dielectric performance compared to the base synthetic ester fluid., Part of proceedings: ISBN 9781119800163, QC 20221115

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%., QC 20220830

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., QC 20220718

This paper reports the experimental and theoretical investigations of particle levitation voltage on thermally aged ester fluid, under AC and harmonic AC voltages, in the presence of both electric and magnetic fields (130 mT and 160 mT). The results indicate a higher sensitivity to identify partial discharge (PD) initiated due to particle movement in aged ester fluids with an ultra-high frequency (UHF) sensor than the fluorescent fiber technique. The cause for the reduction in sensitivity of PD detection due to the fluorescent fiber technique with thermally aged fluid is analyzed using steady-state fluorescent measurement. The reduction in the levitation voltage noticed under high-frequency AC voltages is much more severe than its impact under the fundamental frequency of AC supply voltage. In addition, the presence of a magnetic field reduces the magnitude of levitation voltage substantially. The UHF signals generated due to particle movement-initiated discharges with aged ester fluids indicate a shift in its dominant frequency of 0.9 GHz under the absence of a magnetic field to around 0.6 GHz with the effect of a magnetic field.